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Ventricular stroke volume variation (SVV) is estimated as a function of the standard deviation of arterial blood pressure value measured over each of at least two cardiac cycles, preferably over each of the cardiac cycles in a computation interval covering a full respiratory cycle. In one embodiment, maximum and minimum standard deviation values are determined over the computation interval. SVV is then estimated proportional to the ratio of the difference between the maximum and minimum standard deviation values and the mean of the standard deviation values. In another embodiment, SVV is then estimated proportional to the ratio of the standard deviation of the standard deviation values and the mean standard deviation over the entire computation interval. A pre-processing arrangement for improving reliability of estimates of more general cardiac or hemodynamic parameters is also disclosed and involves smoothing with an approximating function, and sampling and low-pass filtering at an adjustable rate.
1. A method for determining a cardiac parameter equal to or derivable from cardiac stroke volume variation (SVV) comprising:
inputting a waveform data set corresponding to arterial blood pressure over a computation interval that covers at least two cardiac cycles;
calculating a standard deviation value for the waveform data set over each cardiac cycle; and
calculating an estimate of the SVV as a function of the standard deviation values.
2. A method as in
over the computation interval, determining maximum and minimum standard deviation values; and
calculating the estimate of the SVV as a function of the maximum and minimum standard deviation values.
3. A method as in
over the computation interval, computing mean standard deviation value; and
calculating the estimate of the SVV to be proportional to the difference between the maximum and minimum standard deviation values relative to the mean standard deviation value.
4. A method as in
detecting the boundaries of respiratory cycles; and
setting the computation interval to be at least one respiratory cycle.
5. A method as in
computing the standard deviation of the standard deviation values over the computation interval;
computing the mean of the standard deviation values over the computation interval; and
calculating the estimate of the SVV proportional to the ratio between the standard deviation of the standard deviation values and the mean of the standard deviation.
6. A method as in
measuring arterial pressure using a catheter-mounted pressure transducer; and
converting the measured arterial pressure into the waveform data set.
7. A method as in
measuring arterial pressure non-invasively; and
converting the measured arterial pressure into the waveform data set.
8. A method as in
9. A method as in
computing an approximating function that best matches the calculated standard deviation values according to a predetermined metric over at least one of the computation intervals;
creating a set of sampled, approximating values by sampling the approximating function at an interval-specific sampling rate;
low-pass filtering the sampled, approximating values; and
calculating the estimate of the SVV as a function of the low-pass filtered, sampled approximating values.
10. A system for determining a cardiac parameter equal to or derivable from cardiac stroke volume variation (SVV) comprising:
an arrangement for determining and inputting a waveform data set corresponding to arterial blood pressure over a computation interval that covers at least two cardiac cycles;
a processing system including computer-executable code
for calculating a standard deviation value for the waveform data set over each cardiac cycle; and
for calculating an estimate of the SVV as a function of the standard deviation values.
11. A system as in
for determining maximum and minimum standard deviation values over the computation interval; and
for calculating the estimate of th SVV as a function of the maximum and minimum standard deviation values.
12. A system as in
for computing a mean standard deviation value over the computation interval; and
for calculating th estimate of the SVV to be proportional to the difference between the maximum and minimum standard deviation values relative to the mean standard deviation value.
13. A system as in
14. A system as in
for computing the standard deviation of the standard deviation values over the computation interval;
for computing the mean of the standard deviation values over the computation interval; and
for calculating the estimate of the SVV proportional to the ratio between the standard deviation of the standard deviation values and the mean of the standard deviation.
15. A system as in
a catheter-mounted pressure transducer measuring arterial blood pressure; and
conversion circuitry converting the measured arterial pressure into the waveform data set.
16. A system as in
a non-invasive arterial pressure measurement device; and
conversion circuitry converting the measured arterial pressure into the waveform data set.
17. A system as in
18. A system as in
for computing an approximating function that best matches the calculated standard deviation values according to a predetermined metric over at least one of the computation intervals;
for creating a set of sampled, approximating values by sampling the approximating function at an interval-specific sampling rate; and
for calculating the estimate of the SVV as a function of the low-pass filtered, sampled approximating values filtered by the low-pass filter.
This application is a continuation-in-part of, claims priority of, and incorporates by reference U.S. patent application Ser. No. 10/728,705, filed 5 Dec. 2003 now U.S. Pat. No. 7,220,230, and Ser. No. 10/890,887, filed 14 Jul. 2004.
1. Field of the Invention
This invention relates in general to cardiac monitoring and in particular to estimation of ventricular stroke volume variation (SVV) as well as to a system that implements the method.
2. Background Art
Stroke volume (SV), cardiac output (CO), etc., are important indicators not only for diagnosis of disease, but also for "real-time" monitoring of the condition of both human and animal subjects, including patients. Few hospitals are therefore without some form of equipment to monitor one or more of these cardiac parameters. Many techniques—invasive and non-invasive, as well as those that combine both—are in use and even more have been proposed in the literature.
Most of the techniques used to measure SV can usually be readily adapted to provide an estimate of CO as well, since CO is generally defined as SV times the heart rate HR, which is usually available to monitoring equipment. Conversely, most devices that estimate CO also estimate SV as a sub-step.
As is explained in greater detail below, still another cardiac parameter that promises to provide clinically important information is stroke volume variation SVV. One way to estimate SVV is simply to collect multiple SV values and calculate the differences from measurement interval to measurement interval.
One common way to measure SV or CO is to mount some flow-measuring device on a catheter, and then to thread the catheter into the subject and to maneuver it so that the device is in or near the subject's heart. Some such devices inject either a bolus of material or energy (usually heat) at an upstream position, such as in the right atrium, and determine flow based on the characteristics of the injected material or energy at a downstream position, such as in the pulmonary artery. Patents that disclose implementations of such invasive techniques (in particular, thermodilution) include:
U.S. Pat. No. 4,236,527 (Newbower et al., 2 Dec. 1980);
U.S. Pat. No. 4,507,974 (Yelderman, 2 Apr. 1985);
U.S. Pat. No. 5,146,414 (McKown, et al., 8 Sep. 1992); and
U.S. Pat. No. 5,687,733 (McKown, et al., 18 Nov. 1997).
Still other invasive devices are based on the known Fick technique, according to which CO is calculated as a function of oxygenation of arterial and mixed venous blood.
Invasive techniques have obvious disadvantages, the main one of which is of course that catheterization of the heart is potentially dangerous, especially considering that the subjects (especially intensive care patients) on which it is performed are often already in the hospital because of some actually or potentially serious condition. Invasive methods also have less obvious disadvantages: Some techniques such as thermodilution rely on assumptions, such as uniform dispersion of the injected heat, that affect the accuracy of the measurements depending on how well they are fulfilled. Moreover, the very introduction of an instrument into the blood flow may affect the value (for example, flow rate) that the instrument measures.
Doppler techniques, using invasive as well as non-invasive transducers, are also used to measure flow and to calculate SV and CO from the flow measurements. Not only are these systems typically expensive, but their accuracy depends on precise knowledge of the diameter and general geometry of the flow channel. Such precise knowledge is, however, seldom possible, especially under conditions where real-time monitoring is desired.
There has therefore been a long-standing need for some way of determining cardiac parameters such as SV, SVV, etc., that is both non-invasive, or at most minimally invasive, and accurate. One blood characteristic that has proven particularly promising for accurately determining such parameters with minimal or no invasion is blood pressure.
Most known blood-pressure-based systems rely on the so-called pulse contour method (PCM), which calculates an estimate of the cardiac parameter(s) of interest from characteristics of the beat-to-beat pressure waveform. In the PCM, "Windkessel" (German for "air chamber") parameters (characteristic impedance of the aorta, compliance, and total peripheral resistance) are typically used to construct a linear or non-linear, hemodynamic model of the aorta. In essence, blood flow is analogized to a flow of electrical current in a circuit in which an impedance is in series with a parallel-connected resistance and capacitance (compliance). The three required parameters of the model are usually determined either empirically, through a complex calibration process, or from compiled "anthropometric" data, that is, data about the age, sex, height, weight, etc., of other patients or test subjects. U.S. Pat. No. 5,400,793 (Wesseling, 28 Mar. 1995) and U.S. Pat. No. 5,535,753 (Petrucelli,.et al., 16 Jul. 1996) are representative of systems that rely on a Windkessel circuit model to determine CO.
PCM-based systems can monitor SV-derived cardiac parameters more or less continuously, with no need for a catheter (usually right heart) to be left in the patient. Indeed, some PCM systems operate using blood pressure measurements taken using a finger cuff. One drawback of PCM, however, is that it is no more accurate than the rather simple, three-parameter model from which it is derived; in general, a model of a much higher order would be needed to faithfully account for other phenomena, such as the complex pattern of pressure wave reflections due to multiple impedance mis-matches caused by, for example, arterial branching. Because the accuracy of the basic model is usually not good enough, many improvements have been proposed, with varying degrees of complexity
The "Method and apparatus for measuring cardiac output" disclosed by Salvatore Romano in U.S. Published Patent Application 20020022785 A1 (21 Feb. 2002, "Method and apparatus for measuring cardiac output") represents a different attempt to improve upon PCM techniques by estimating SV, either invasively or non-invasively, as a function of the ratio between the area under the entire pressure curve and a linear combination of various components of impedance. In attempting to account for pressure reflections, the Romano system relies not only on accurate estimates of inherently noisy derivatives of the pressure function, but also on a series of empirically determined, numerical adjustments to a mean pressure value.
Fluid administration in hemodynamically unstable patients is often a major challenge when it-comes to measuring SV, CO, or other hemodynamic parameters in real time. Correct clinical assessment of hypovolemia is difficult, as is the decision to undertake fluid resuscitation as the initial treatment strategy. Specifically, it is very difficult to predict whether a hemodynamically unstable patient will respond to fluid therapy with an increase in stroke volume and cardiac output. Moreover, fluid overload can cause significant pulmonary or cardiac dysfunction, whereas fluid insufficiency may cause tissue damage resulting in vital organ dysfunction. A patient's fluid responsiveness is the major and most important determinant to assess the adequacy of fluid resuscitation therapy and to ensure optimal cardiac performance and organ perfusion.
Many bedside indicators of ventricular preload have been used as predictors of fluid responsiveness. Right arterial pressure (RAP) and pulmonary artery occlusion pressure (PAOP) are the most commonly used in the intensive care unit (ICU) when deciding to administer fluids. Other bedside indicators of ventricular preload include right ventricular end diastolic volume (RVEDV) and left ventricular end diastolic area (LVEDA) measured with transesophageal echocardiography. Several studies and case reports have shown, however, that these static indicators based on cardiac filling pressures have poor predictive value and often fail to give adequate information about fluid responsiveness.
Recently, several studies have confirmed the clinical significance of monitoring the variations observed in left ventricular stroke volume that result from the interaction of the cardiovascular system and the lungs under mechanical ventilation. These stroke volume variations (SVV) are caused by the cyclic increases and decreases in the intrathoracic pressure due to the mechanical ventilation, which lead to variations in the cardiac preload and afterload. SVV has recently been extensively investigated and several studies have shown the usefulness of using SVV as predictor of fluid responsiveness in various clinical situations. Several other parameters based on SVV have been found to be useful as well. In particular, systolic pressure variation (SPV) with its delta-Up (ΔUp) and delta-Down (ΔDown) components has been found to be a very useful predictor of fluid responsiveness. SPV is based on the changes in the arterial pulse pressure due to respiration-induced variations in stroke volume. Yet another parameter that has recently been investigated and shown to be a valid indicator of fluid responsiveness is the pulse pressure variation (PPV).
Recent developments in arterial pulse contour analysis methods have opened unique opportunities for less-invasive, continuous and real-time estimation of SVV. This allows clinicians to use SVV routinely along with SV and CO in their assessment of the hemodynamic state of critical care patients.
Existing systems for measuring fluid responsiveness based on respiration-induced changes in the arterial pulse pressure are almost all based on one of only a few methods. Some of the methods described in the literature include the following measurement of Pulse Pressure Variation (PPV), Systolic Pressure Variation (SPV) and Stroke Volume Variation (SVV).
PPV estimation is based on some version of the following Equation 1:
SPV estimation is based on some version of the following Equation 2:
Similarly, SVV estimation is based on some version of the following Equation 3:
In Equations 1, 2, and 3, the denominators are the averages of the maximum and minimum values of PP, SP and SV, respectively. In other words, the denominators are mean values, albeit of only two measurement points. This simple averaging of extreme values has been most common merely to simplify the calculations, which have typically been performed by hand. More reliable values may be obtained, however, by using the mean of all the measurement values over the measurement interval, that is, the first statistical moment of PP, SP, and SV.
Thus, for each of PPV, SPV and SVV, the respective variation value formula expresses the magnitude of the range of the value (maximum minus minimum) relative to the mean of the extreme (maximum and minimum) values.
The specific monitoring of SVV has both specific difficulties and advantages. Physiologically, SVV is based on several complex mechanisms of cardio-respiratory interaction. In brief: mechanical ventilation causes changes in left ventricular preload, which leads to distinct variations in left ventricular stroke volume and systolic arterial pressure. Monitoring of SVV enables prediction of left ventricular response to volume administration and helps with correct assessment of hypovolemia and the subsequent decision to undertake volume resuscitation in many critical situations.
In addition to the three methods listed above, there is a fourth method, known as Perel's method, which is generally called the "respiratory systolic variation test." This method involves airway pressure maneuvers, such as inducing tidal volumes of varying amplitudes preceded by a short apnea period. U.S. Pat. No. 5,769,082 (Perel) describes this method. Because of the requirement for pressure maneuvers, this method is not suitable for real-time monitoring.
The methods listed above are implemented in some CO monitoring instruments such as LiDCO Ltd.'s cardiac monitor and the PiCCO system of Pulsion Medical Systems (see, for example, U.S. Pat. No. 6,315,735—Joeken et al), both of which rely on Equation 3. Tests by the inventors show however, that these methods are so noisy that they do not allow for accurate real-time monitoring of the respiration-induced changes in the arterial pulse pressure. The main reason for the noise problems in the SVV estimation in those instruments is the way SV is calculated. For example, the PiCCO system uses a beat-to-beat stroke volume estimation method based on a pulse contour algorithm that involves detection of specific points in the blood pressure waveform, such as the dicrotic notch. Precise detection of the dicrotic notch and other points in the blood pressure signal, however, is difficult, due to the inconstancy of the blood pressure waveform and its volatile nature.
What is needed is therefore a system and method of operation for estimating SVV in real time more accurately and robustly than is now possible, using at most minimally invasive techniques. This invention meets this need.
The invention provides a method and related system implementation for determining a cardiac parameter equal to or derivable from cardiac stroke volume variation (SVV): A waveform data set corresponding to arterial blood pressure, determined either invasively or non-invasively, is determined and input to a processing system over a computation interval that covers at least two cardiac cycles; a standard deviation value for the waveform data set is then calculated over each cardiac cycle; and an estimate of the SVV is calculated as a function of the standard deviation values.
Different methods may be used to calculate the values used in the SVV estimation. For example, maximum and minimum standard deviation values over the computation interval may be determined, and the estimate of the SVV can then be calculated as a function of the maximum and minimum standard deviation values. A mean standard deviation value is preferably also computed over the computation interval and the estimate of the SVV can then be calculated to be proportional to the difference between the maximum and minimum standard deviation values relative to the mean standard deviation value. As one alternative, the processing system may compute the standard deviation of the standard deviation values over the computation interval and then estimate the SVV as being proportional to the ratio between the standard deviation of the standard deviation values and the mean of the standard deviation values.
Blood pressure may be measured either invasively or non-invasively, for example by using a catheter-mounted pressure transducer or a finger cuff. The measured arterial pressure is then converted into the waveform data set.
The inventors have also found that the above-described method according to the invention may also be used to calculate an estimate of right ventricular end diastolic volume, which is inversely proportional to the calculated estimate of the cardiac stroke volume variation.
According to one feature of the invention that has been found to be advantageous, an approximating function is computed that best matches the calculated standard deviation values according to a predetermined metric over at least one of the computation intervals. The approximating function is then sampled at an interval-specific sampling rate to create a set of sampled, approximating values, which are then low-pass filtered before the estimate of the SVV is computed from them.
This method of approximating, resampling and low-pass filtering with an adjustable rate may be extended for use in estimating other cardiac or hemodynamic parameters than SVV, for example, systolic pressure variation, pulse pressure variation, etc. In this case, the waveform data set is generated and input to the processing system to correspond to whatever measurement parameter is selected. A series of measurement values is then generated from the waveform data set; an approximating function is computed that best matches the measurement values (or some function of them) according to a predetermined metric; over each of at least one computation interval, a set of sampled, approximating values is then created by sampling the approximating function at an interval-specific sampling rate; the sampled, approximating values are then low-pass filtered; and an estimate of the output value is then computed as a function of the low-pass filtered, sampled approximating values.
In broadest terms, the invention involves the beat-to-beat of stroke volume variation SVV as a function of the standard deviation of the blood pressure waveform over a plurality of cardiac cycles. Of course, the invention may be used to determine any other cardiac parameter that can be derived from SVV.
The invention may be used to advantage with any type of subject, whether human or animal. Because it is anticipated that the most common use of the invention will be on humans in a diagnostic setting, the invention is described below primarily in use with a "patient." This is by way of example only, however—it is intended that the term "patient" should encompass all subjects, both human and animal, regardless of setting.
Because of its clinical significance, it is anticipated that most implementations of the invention will generate SVV estimates based on measurements of systemic arterial blood pressure. It would also be possible to use measurements of blood pressure taken elsewhere, however, such as in the pulmonary artery on right side, although such sites may require invasive intracardiac measurement.
Pressure Waveforms
According to the invention, P(t), or any signal that is proportional to P(t), may be measured at any point in the arterial tree, either invasively or non-invasively. If invasive instruments are used, in particular, catheter-mounted pressure transducers, then any artery may be used as a measurement point. Placement of non-invasive transducers will typically be dictated by the instruments themselves—the placement of finger cuffs, upper arm pressure cuffs, and earlobe clamps should be obvious. Regardless of the instrument, it will ultimately produce, or cause to be produced, an electric signal corresponding (for example, proportional) to P(t).
Rather than measure arterial blood pressure directly, any other input signal may be used that is proportional to blood pressure. Any needed scaling or conversion may then be done at any or all of several points in the calculations described below. For example, if some signal other than arterial blood pressure itself is used as input, then it may be calibrated to blood pressure before its values are used in the computations described below. In short, the fact that the invention may in some cases use a different input signal than a direct measurement of arterial blood pressure does not limit its ability to generate an accurate SVV estimates. The only requirement of this invention is that a signal or data set equal or at least having a known relationship to (such as being proportional to) the patient's blood pressure over the interval of interest (including continuously) must be made available to the processing system (see below) that carries out the signal conditioning and various calculations described below.
As is well known, and as is illustrated in
Standard Deviation
The calculation of the mean and standard deviation of a continuous or discrete function or data set f is a very well known procedure, and is usually indicated in references by the Greek letters μ and σ, respectively, or, in most programming languages, by function names such as mean and std. Thus, μ(f) and mean(f) represent the mean of the function or data set f over some interval and σ(f and std(f) represent its standard deviation.
Now consider the calculation of the mean and standard deviation of a series of blood pressure values P=P(k) over some interval such as k=1, . . . , n. The most common way to calculate the mean μ(P) and standard deviation σ(P) is to use the algorithms familiar to all who have taken even an introductory course in Statistics:
As will become clearer below, the invention generates a robust estimate of SVV in real time from calculations of the standard deviation of the pressure waveforms, preferably over several cardiac cycles. Although the standard "textbook" formula for standard deviation (Equation 5) is preferred for well known statistical reasons, any formula or algorithm that provides an acceptably accurate value of or corresponding to standard deviation may be used instead in the invention. For example, at least in the context of blood pressure-based measurements, a rough approximation to σ(P) can be had by dividing by three the difference between the maximum and minimum measured pressure values. Moreover, the maximum, or absolute value of the minimum, of the first derivative of the P(t) with respect to time is generally proportional to σ(P).
In this discussion of the invention are several references to calculations using "pressure" values and "standard deviation" values. In the preferred embodiment of the invention, these are in fact direct measurements of blood pressure, in particular arterial blood pressure, and standard deviation as computed using the most common formula, given above as Equation 5. It is to be understood, however, that "pressure" may equally refer to indirect measurements, or measurements of some physiological characteristic that correlates or corresponds to or can be otherwise related to pressure. Similarly, "standard deviation" may also refer to any value known to approximate the value that would be given by the usual formula; examples of such alternatives are given in the previous paragraph.
SVV Computation
The standard formula for calculating cardiac output (CO) is CO=SV�HR, which simply expresses relationship that the amount of blood the heart pumps per minute is equal to how much it pumps per cycle (SV) times the number of cycles in a minute. Given HR, the problem, of course, is that this assumes a constant value of SV, or knowledge of the mean SV. Based on the observation that the pulsatility of a pressure waveform is created by the cardiac stroke volume into the arterial tree, one of the present inventors earlier discovered that SV can be approximated as being proportional to the standard deviation of the arterial pressure waveform P(t), or of some other signal that itself is proportional to P(t). Thus, one way to estimate SV is to apply the relationship
Substituting Equation 6 into Equation 3 yields a formula for SVV that is a function of std(P):
As mentioned above, using the statistical mean of pressure—mean(P)—in the denominator over the measurement interval will generally provide more accurate and robust estimates than using the mean only of the maximum and minimum values, although the invention may use either mean in the denominator. The preferred form of Equation 8 is thus:
If no such external device is present, then the beginning of each cardiac cycle can also be determined using software alone from the pressure waveform P(k) itself, for example, simply by assuming that each beat begins at the time of minimum (diastolic) pressure Pdia (see
Let P(k,i) be the i'th beat-to-beat arterial pressure signal in a computation interval. The standard deviation std(P(k,i)) can then be computed as described above and will be a single-value (scalar) result. The standard deviation values for each of the beat-to-beat arterial pressure signals in the computation interval can be similarly computed. In
Computation of SVV according to Equation 9 requires the maximum, minimum and mean values of std(P(k,i)) for each computation interval. One way to get std(P)max and std(P)min for a given-respiratory cycle (roughly three respiratory cycles are illustrated in
During actual monitoring, noise and other factors may cause one or more std(P(k,i)) values to become unreliable. Deviant and potentially unreliable std(P(k,i)) values can be detected using known algorithms, such as those based on pattern-matching. Interpolation can then be used to determine replacements for the excluded value(s). A preferred method for smoothing and filtering measured values to increase reliability—applicable even in determinations of other cardiac and hemodynamic parameters than SVV—is described below.
Any standard algorithm may be used to identify std(P)max and std(P)min from std(P(k,i)). The simplest method is to take the greatest and least measured values. Alternatively, the measured std(P(k,i)) points may be used as the basis for determining an approximating or smoothing function (for example, using splines or polynomials); this would in many cases allow for identification of extreme std(P(t)) values that lie between the computed values, such as std(P)min shown in
As mentioned above, the preferred computation interval is one respiratory cycle. The beginning and end times of these cycles may be detected using any known device. Note that many patients who would need this invention will also be ventilated, in which case the ventilator itself may provided the needed timing signals for the invention to separate the different respiratory cycles.
As illustrated in
Computation Interval—Alternative SVV Computation
Above, it is assumed that an SVV value is estimated for each respiratory cycle. This is not necessary. Rather, it would also be possible to use the same methodology and equations described above to compute a single SVV value over a computation interval greater than one respiratory cycle, even over the entire time of a monitoring session. Although this would of course not show cycle-to-cycle SVV trends, it may provide more accurate results for each monitoring session and thus better indication of more long-term (such as session-to-session or day-to-day) trends. It is not necessary always to compute over "extremes" intervals, however. Rather, an SVV value could be computed for any n-cycle time periods, with n ranging from one (the case described above) upward.
Assume, for example, that a computation period is greater than one respiratory cycle. For the sake of illustration, assume that all three respiratory cycles shown in
This alternative, multi-cycle method does not require the system to determine any std(P)max or std(P)min values. Consequently, it is not even advantageous to determine an interpolating, approximating function for the std(P(k)) values over the computation interval.
Optional Smoothing, Resampling and Filtering
The measurement values will seldom fall neatly on a well-defined profile, since the underlying parameter is affected not only by noise, but also by natural irregularities such as a non-constant heart rate, different respiration patterns, etc. In many cases, the measurement system may itself be able to warn of, identify and exclude unreliable measurement values. For example, if signal strength falls below some predetermined minimum, then the values of the parameter measured during such time may be tagged or excluded. In other cases, unreliable values may be undetectable without further analysis. In
As mentioned above, one way to identify deviant values is by using pattern matching, in which the measured points are compared with one or more pre-stored templates, obtained from controlled studies done for a patient population, or simply verified profiles measured in the same patient. Any point that deviates from the template(s) by more than some threshold amount, measured in any known manner, can then be excluded.
In the preferred embodiment of the invention, for each computation interval, an approximating function (which may be the concatenation or combination of more than one partial function) is generated so as to create an interval profile that best matches the measured points according to any known metric, that is, in any known sense, such as least squares. For example, polynomial functions such as splines (two examples: B-splines and Bezier curves), reduced-component Fourier representations, etc., may be quickly calculated to generate an appropriate approximating function. In
In the illustrated examples, the computation interval is a respiratory cycle. Other intervals may be chosen depending on the parameter of interest, and need not necessarily be related to the respiratory cycles at all. Even for those that do, it is not necessary for the measurement interval to be a single cycle, or a whole multiple of single cycles, although this will in general make the most sense where the parameter of interest is affected by respiration and will also generally simplify calculations.
Once the approximating function is computed, the preferred embodiment of the invention low-pass filters the values per computation interval. The theory and implementation of digital low-pass filters is well known. Some set of sampled values are used as inputs to an algorithm that calculates some weighted linear or rational function of them to produce a transformed, filtered set of output values. Typical digital filters generally assume a constant "distance" between samples, however, and most such filters also have fixed coefficients.
According to this aspect of the invention, however, the input values to the low-pass filter are obtained by sampling the approximating function—possibly (but not necessarily) even at a higher rate than the rate at which the actual measurement values were obtained. In
Note that this procedure enables even spacing of the sample points, even though, because of a changing heart rate, for example, the actual measured values may not be evenly spaced. Moreover, note that the sampling rate for respiratory cycle (here chosen as the computation interval) 3 is greater than that for cycles 1 and 2. One way to select the sampling rate for each given computation interval is to choose as many evenly spaced samples of the approximating curve X*(t) as there are actual measurement values in the computation interval. This is not necessary, however, but rather the sampling rate may be chosen as desired, for example, to satisfy the Nyquist criterion and reduce aliasing effects for the type of digital low-pass filter used.
Tests by the inventors have shown that these steps of smoothing (via the approximating function), re-sampling (that is, sampling that occurs after that performed for the analog-to-digital conversion), and adjustable-coefficient low-pass filtering, improve the ability of the invention to reject noise and produce more reliable SVV values. As mentioned above, the procedure may also be used for other estimated parameters than SVV.
System Components
The signals from the sensors 100, 200 are passed via any known connectors as inputs to a processing system 300, which includes one or more processors and other supporting hardware, such as a memory 301, and system software (not shown) usually included to process signals and execute code. The invention may be implemented using a modified, standard, personal computer, or it may be incorporated into a larger, specialized monitoring system. In this invention, the processing system 300 also may include, or is connected to, conditioning circuitry 302 which performs such normal signal processing tasks as amplification, filtering, ranging, etc., as needed.
The conditioned, sensed input pressure signal P(t) is then converted to digital form by a conventional analog-to-digital converter ADC 304, which has or takes its time reference from a clock circuit 305. As is well understood, the sampling frequency of the ADC 304 should be chosen with regard to the Nyquist criterion so as to avoid aliasing of the pressure signal; this procedure is very well known in the art of digital signal processing. The output from the ADC 304 will be the discrete pressure signal P(k), whose values may be stored in conventional memory circuitry (not shown).
A signal pre-processing module 306 is preferably included, with routines to provide such known pre-processing as digital filtering for general (as opposed to interval-to-interval) noise removal, for motion artifact rejection, pulse beat detection (if needed), for rejection of bad beats, etc. This module may also be implemented wholly or partially in hardware. As mentioned above, known circuitry may be included to indicate, for example, that signal strength is too low, and that the delivered measurement values are unreliable. As such, the module 306 may also be located functionally, wholly or partially, before the ADC 304.
The values P(k) are passed (usually, accessed from memory by) to a software module 310 comprising computer-executable code for computing the standard deviation of P(k) over a computation interval such as a cardiac cycle, which may be _ triggered by any known device or software routine 315 that detects heart rate or at least signals the beginning of a cardiac cycle. Even moderately skilled programmers will know how to design this software module 310.
Above are described preferred, but optional processing steps of generating an approximating function (see X*(t) in
The std(P(k)) values, which will typically be stored in the memory 301, are then passed to a software module 320 that includes computer-executable code for detecting the maximum, minimum std(P(t)) values std(P)max and std(P)min and for computing the mean std(P(t)) value mean(std(P(k)) for each given computation/measurement interval, which may be triggered by a respiratory device 325 such as a ventilator or detected by a software module as described above. Again, even moderately skilled programmers will know how to design the software module 320 given the description above. Also as noted above, if the computation interval is chosen to extend over more than one respiratory cycle, then it will not be necessary to calculate the maximum and minimum std(P(t)) values std(P)max and std(P)min such that the module 320 can be omitted or at least not called.
The values std(P)max, std(P)min and mean(std(P(k)) are then passed to an SVV calculation module 330, which computes an estimate of SVV for the chosen interval according to Equation 8 or 9. If a multi-cycle interval is set, then the SVV calculation module 320 may operate directly on the std(P(k)) values provided by module 310 to calculate an estimate of SVV according to Equation 10.
As shown in
The invention further relates to a computer program loadable in a computer unit or the processing system 300 in order to execute the method of the invention. Moreover, the various software modules 310, 312-314, 315 (if implemented in software), 320, 330, or, in general, 370, used to perform the various calculations and perform related method steps according to the invention may also be stored as computer-executable instructions on a computer-readable medium in order to allow the invention to be loaded into and executed by different processing systems.
Once an SVV (or other cardiac or hemodynamic) estimate has been computed, it is passed to any desired output device 500, such as a user-viewable monitor, and displayed, stored or transmitted in any chosen format. An input device 400 is preferably also included to allow the user to input, for example, administrative and patient-specific information, to adjust the display, to choose the computation interval, etc. Note that if the user is to be allowed to change the computation interval, then the corresponding information must be made available to the estimation software component 370 so that it can direct the SVV estimation module to select the required input values when computing SVV according to either Equations 8 or 9, or Equation 10.
Test Results
Two different but related methods for computing SVV from std(P(k)) values are described above—one in which SVV is calculated for over single respiratory cycles and another that may be used to compute a single SVV value for a computation interval spanning more than one respiratory cycle. The inventors tested both these embodiments of the invention on animal femoral and radial blood pressure data. The data were collected from several pig experiments, which were performed in a laboratory. During the experiments, several changes in the left ventricular volume were induced (such as volume infusions or volume extractions). Variations of the peripheral resistance (vasodilation or vasoconstriction) were induced as well. Both embodiments of the invention were found not only to provide similar SVV estimates, but also these estimates were found to be superior to those obtained using prior art methods for the sake of comparison.
Additional Outputs
As mentioned above, the invention may be used to estimate not only SVV, but also any cardiac parameter that can be derived from SVV. The inventors have discovered in tests, for example, that during mechanical ventilation with a constant ventilation rate and a constant tidal volume the right ventricular end diastolic volume (EDV) is an inversely proportional to SVV. Thus:
The calibration factor c in Equation 11 will depend on several parameters such as ventricular contractility and ventricular compliance. In general, c will depend on the hemodynamic state of the patient. Recalibration must therefore be performed each time the hemodynamic status of the patient changes or during periods of hemodynamic instability.
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David Filner on Classical Music
David Filner assumed the administrative leadership of the San Antonio Symphony in November, 2012. Led by Music Director Sebastian Lang-Lessing, the San Antonio Symphony is celebrating its 73rd year this season.
Monthly Archive for November, 2012
More on Tal
The Express-News carried a beautiful article about flutist Tal Perkes, who died on October 20 at the age of 51. You can read it by clicking here. His mother was quoted about his childhood motivation, "Like kids everywhere, he didn't want to practice, but he discovered if he did practice, the little girls would gather […] [Read More]
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subset: commoncrawl


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Dr Wendy Dackson now has her own blog. Although I hope she will continue to write for us as well, sometimes her pearls of wisdom are too lustrous not to share!
Originally posted on Past Christian:
Yesterday on Facebook, Lay Anglicana shared the Archbishop of Canterbury's speech at Britain's National Parliamentary Prayer Breakfast. I'm sure that there will be a lot of commentary on the finer points of global Christianity from people with much more official authority than I have. But a few things stood out for me, and I want to write a bit on them.
The first (not in order of where it falls in ++Justin's speech, but in what captured my attention) is the idea of good disagreement. The Archbishop used the phrase in the context of how the Anglican Communion holds together, and his words were as follows:
We deal in thousands of cultures. The struggle, the achievement, of holding together in good disagreement sets a pattern in which truth is not a club with which to strike others, but a light freely offered for a path of joy and flourishing.
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Just months before the original Mac debuted 30 years ago, it was deeply troubled by an in-house 5.25″ flimsy floppy-disk drive it relied on called the Twiggy (you know, for it's flimsiness). This was replaced by a more stable 3-inch Sony drive before shipping, but the Twiggy Macs had more than just a different drive.
Interestingly, the operating system featured a Steve Jobs rendtion of Microsoft's dreaded, now retired Clippy assistant. The Ashton Kutcher resemblance has never been clearer… er… pixelated.
Check out the full article for other tidbits at Cult of Mac (via Daring Fireball).
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6 Responses to "Steve Jobs was almost Clippy and other things learned from prototype Twiggy Macs"
That would have ruled. Damn!
How was it dreaded? I had the little dog instead of clippy. I kind of miss that. It made my PC at work feel a little more human.
From the looks of it, these are just normal requesters that happen to include hints in brackets, While Clippy was something that was just popping up at seemingly random times, guessing what the user was up to and then making half-assed suggestions, about how to achieve this. "Looks like you are trying to write a letter…"
To the user Clippy was more like the annoying version of Mr. Macintosh: http://www.folklore.org/StoryView.py?story=Mister_Macintosh.txt
Intrestinly enough: The Mac version of MS Word (even up to the first version for OS X) used to have Clippy replaced with a small 3D mascot that looked like the original macintosh.
The text would've been more like: Steve Sez "You suck at computer, why am I talking to you, your work is shit!"


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Release: 11/15/2013
RIVERSIDE, Utah — Time for Terre Haute.
After registering top-notch results at the NCAA Mountain Region Championships Friday, the University of New Mexico's nationally ranked cross country teams are in position to move onto the national championships next week.
The Lobo women placed second behind individual champion Sammy Silva and will automatically advance to the NCAA Championships next Saturday in Terre Haute, Ind., while the men will have to earn an at-large bid after placing third overall.
However, the 11th-ranked men should grab an at-large spot via their regular-season résumé, which would make it five straight years New Mexico has sent both teams to the NCAA Championships.
The No. 8 women have qualified six years in the row, dating back to 2008.
"There can't be many teams that have done that," Lobo head coach Joe Franklin said. "It's just what we try to do. We just get better and better and better. And I think we're slowly doing that."
New Mexico is just one of six schools — along with Colorado, Stanford, Florida State, Georgetown and Villanova — to have sent both their men's and women's teams to the NCAA Championships from 2009 to 2012.
But at this meet, New Mexico was just focusing on moving on.
And for the women, they did exactly that.
Heading into the meet as the region's top team, the Lobos essentially needed to run like they have all season to secure one of the automatic bids. Despite No. 10 Colorado challenging the women for the team title, New Mexico managed to ride their remarkable team parity to a runner-up team finish.
"The women ran OK," Franklin said. "We had some a couple of really, really solid races and we had some average races. But the nice thing is that if this is your average day, that's a pretty good day."
Sammy Silva led the women at Schneiter's Riverside Golf Course, winning the six-kilometer race in 20 minutes, 29.3 seconds. Silva is the first UNM harrier to win a women's region race since Lisa Mitchell did it in 1981.
Charlotte Arter was close behind and ran to a third-place finish of 20:34.8. Together, Silva and Arter are the first UNM women's duo to claim two top-three finishes at a regional meet.
"They looked very comfortable," Franklin said of the top two finishers.
Calli Thackery, Tamara Armoush and Nicole Roberts rounded out the women's scorers, with Thackery (20:57.6) in 13th place, Armoush (21:05.6) in 18th and Roberts (21:33.9) in 29th.
Nicola Hood (35th place, 21:30.0) and Heleene Tambet (36th, 21:31.2) also placed for UNM.
The women combined to score 69 points, which is their second-lowest score in 35 years behind a 53-point effort to win the meet in 2010. They were also able to turn in their second straight second-place showing at the Mountain Region Championship.
Overall, Colorado also grabbed an automatic bid and took the women's team title with a score of 29 points. BYU (109 points) was third, host Weber State (160) fourth and Air Force (185) fifth.
For the women, this will be their sixth straight appearance at the NCAA Championships and 10th overall, counting two trips to the AIWA championships. The Lobos finished 10th in last year, ninth in 2011, fifth in 2010, 13th in 2009 and 18th in 2008 in their string of NCAA appearances under Franklin.
Unlike the women's race, the men's race was far more competitive, with seven nationally ranked teams — including the nation's top two teams, No. Colorado and No. 2 Northern Arizona — dueling for two automatic berths.
Still, the men were able to outdo their regional rank of fourth, as they placed third overall.
"They guys ran phenomenally and very comfortably, which was nice," Franklin said. "It looked like a Friday practice."
Luke Caldwell, for the eighth time in the last nine races in which he has competed, led New Mexico over the 10-kilometer course with a clocking of 29:46.1.
But the Mountain West individual runner up wasn't alone, as Adam Bitchell took eighth in 29:47.2. It's the first time since the men won the meet in 2010 that UNM recorded two top-10 finishers.
The Lobos also relied on their parity, as all five scorers placed in the top 25. Patrick Zacharias (29:54.2) was 17th, Sean Stam (30:04.5) 23rd and Elmar Engholm (30:07.1) was 25th.
Ross Matheson (49th place, 30:44.2) and Donovan Torres (58th, 30:59.7) rounded out the Lobos' scorers.
As a team, the men tallied 79 points, just 10 points behind second-place Colorado (69 points) and 18 behind winner Northern Arizona (61 points).
However, the team performance the men rolled out, which included a spread of just 21 second among the five scorers, impressed Franklin.
"They just did a really good job," he said. "If that performance, or something similar to that, happens in a week [at the NCAA Championships], they're going to be really high up in the team score."
31 teams are selected to participate in each championship. The top two teams from each of the nine regions automatically qualified to the NCAA Championships, for a total of 18 teams. 13 additional teams will be selected at-large based off of those teams regular-season wins over other institution's squads.
The meet is next Saturday, November 23, at the LaVern Gibson Championship Cross Country Course in Terre Haute, Ind.


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Jail for knife attack by Camelford man who saw red
Posted: March 06, 2013|
A MAN from Camelford who "saw red" after a rape allegation and wounded an innocent student has been jailed for nine months.
Paul Rosen, 37, who believed that a relative had been raped, armed himself with a knife and attacked student Mohammed Abdul Malek as he left an Indian restaurant in Tintagel.
"This was a knife attack on an innocent man," said Judge John Neligan at Truro Crown Court, on Friday.
"It was obviously out of character but the use of a knife cannot be excused – custody must be immediate.
"I give you maximum credit for your plea of guilty to attempted wounding with intent, and take account of your glowing references and the probation officer's report, and that, mercifully, the injuries your victim suffered were nowhere near as serious as they might have been."
As he jailed Rosen, of Fore Street, Camelford for nine months, Judge Neligan added: "As your employers value you so much I have no doubt your job will be kept open for you."
Philip Lee, for the prosecution, said that Mr Malek was attacked in an alleyway.
He did not know Rosen and, to protect himself, grabbed the knife with both hands as they struggled, suffering cuts and scratches on his fingers and arms.
"I thought he was going to kill me," the attacked man told police officers afterwards.
When arrested, Rosen explained that there had been a rape allegation and he had "just seen red" and so he had picked up the knife to threaten the man.
There was no suggestion that Mr Malek had been involved and no suspect had ever been identified, added Mr Lee.
Martin Pearce, for the defence, told the court that Rosen was genuinely remorseful.
He asked the Judge to suspend the sentence.
"He was not thinking straight, it was not a case of attempted robbery and was not committed in drink, it just happened in the heat of the moment," said Mr Pearce.
The Cornish Guardian reported in December that the owner of an Indian restaurant in Tintagel said he was doing everything in his power to help police to trace a former member of his staff who was accused of sexually assaulting a young girl.
Police are continuing their investigations into the alleged assault on the young teenager in the kitchen of the restaurant on August 18 last year.
A restaurant worker in his early twenties, who is wanted for questioning, left the village soon after the incident was said to have taken plance and is now believed to be in France.


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Junior forward Edwin Rivas in coming off of his most successful season at Northridge. In 2012, Rivas finished second on the team with 20 points after scoring a career-high eight goals and adding four assists. He was named to the 2012 All-Big West Conference First Team, as well as the 2013 Preseason All-Big West Conference Team. As a sophomore, Rivas helped the Matadors win the Big West Championship for the first time since 2005 and finished tied for third in the league in points, points per game and goals scored. Prior to the start of the season, Rivas sat down with the CSUN Media Relations staff to discuss his preparation and goals for the season.
Q: Coming off of a Big West Championship last season and an All-Big West First Team selection, what are you looking forward to this year to help the team get back to the postseason?
A: Individually, I will play my role and try to do the best I can to help the team however they need. I need to focus and execute. This season is about how hard I can work for the team and what I can do for my teammates.
Q: With the graduation of a number of starters last season, particularly on defense, how your teammates coming together in the offseason to be ready for this year?
A: We have to lead ourselves before we can lead others. In that respect, the returners are helping each other in any way to get better in order for us to help the newcomers get to our level of familiarity. We have already picked right up from where we left off last year and we are ready to get going.
Q: In the offseason you did a lot of individual work in terms of training. What is the one thing that you bring more to the table this year that you feel was missing?
A: For me, it is more about the team effort. It is less about performing individually and more for how we succeed as a team. It is an all-around effort for assists, goals, helping out on defense. Any way that I can help to achieve our goal of winning the Big West Championship again, I will.
Q: The Preseason Big West Coaches Poll picked the Matadors to repeat as champions in the South Division. What pressure or motivation does that give to you and the team to exceed expectations and take things to the next level?
A: We take things step-by-step and day-by-day. We focus on going practice to practice. It is an honor to be picked as favorites because it shows we have proven ourselves in building the program back over the last few years. There's motivation to keep it up but there's no pressure. We know what we are capable of and it's up to us to get it done.


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A bold and dramatic combination of colors and shapes highlight the elegant splendor of this Stacy Garcia pendant light.
This sleek pendant light fixture features a great contemporary look. It comes with a custom-printed giclee style shade. The shade has an acrylic diffuser inside that shields the three bulbs. Canopy and accents are in a brushed steel finish. U.S. Patent # 7,347,593.
Our associates are standing by to assist you.


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Billy Ward here!
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Drum Mum
Join Date: Jan 2012
Posts: 62
Re: Billy Ward here!
It was a real pleasure to see you on this site, Billy!
I hope I'm not mistaken in this, but in one of your books, you described in some detail a lesson you once took with Elvin Jones. What I took away from that story was how you marvelled at his tone. You mentioned that, even though he was playing a sort of rag-tag practice kit, he managed to make that kit sound amazing! I also recall your discussion of the importance of tone.
I'm a relative beginner-playing about four years-but for some reason, I'm really starting to think about this, and some of the other perhaps less-thought-of aspects of playing. I guess I'm just tired of playing and hearing it back as if I'm hitting a cardboard box-no offense to boxes, though!
Could you recommend any exercises or stick techniques that might start me off on helping to improve my tone? It's something I'd like to explore, but know little or nothing about how to do it. I will also say that, although not financially able to take lessons consistently, I'm considering getting with a teacher, even if only once a month. Thanks for your inspiration!
Drum Mum
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Private Foundations are Not Always Forever
Written on October 9, 2013 – 6:09 am | by Malcolm Burrows
Private foundations are assumed to be durable entities. Ever since charitable trusts broke the "rule against perpetuities" in nineteenth century Britain the idea of a privately funded philanthropy has been associated with longevity. Canada Revenue Agency (CRA) data on private foundations, however, shows that 2,089 private foundations closed during the period 1991 to 2013.
There are currently 5,290 private foundations registered in Canada. Over the past decade the private foundation has been the fastest growing category of registered charities. Private foundations are being created at an unparalleled rate, but at times the operating challenges are under-estimated.
Let's start with the 32 private foundations that were revoked by CRA for cause since 1998. Reasons cited include participation in tax shelters, lapse incorporation that invalidated the registration as a charity, receipting infractions, and private benefit. The most common reason listed is inadequate books and records, which is often CRA's "gotcha" rationale masking some other complaint.
The next category contains the 987 private foundations that were revoked for failure to file the annual charity return or T3010. These foundations may reapply, but if a foundation stays on this list it is a sign of exhaustion. A failure to file is either deliberate, indicating an organizational death wish, or inadvertent, indicating a charitable mission that has faded or become too burdensome to pursue.
The largest cohort is the 1070 private foundations that filed for voluntary revocation. While CRA does not provide details, my experience has been that has been that these are foundations that are intentionally short-term, or run out of charitable steam, or never secure expected funding. The high hopes of founders may prove burdensome for future generations of directors/ trustees to implement. The monetary value of the foundation may be inadequate for the purpose, or there is no clear director/trustee succession plan, or, simply, there is no administrative support.
There is no shame in a private foundation running its course – all human institutions do. Often the most responsible action is dissolution and redirecting funds to other charities. That said, looking at the bones of the 2,089 closed private foundations suggests that there are challenges associated with operating private foundations. Estate plans that include private foundations need to consider both purpose and operations. Governance, succession planning, and management are necessary elements if the foundation is going to have a future as a standalone entity.
Tags: Canada Revenue Agency, Malcolm Burrows, Philanthropy, private foundations


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Lott honored for 700 career wins
By Amanda Lowrance
Many coaches only hope to achieve what Coach Jerry Lott of the McNairy Central Lady Bobcats has accomplished in his career.
Lott was honored with a plaque handed to him by Athletic Director Danny Day in front of the crowd that had just witnessed a win over the Wayne County Lady Wildcats on Saturday night.
The audience clapped their hands and "Jerry, Jerry, Jerry" chanted from the student body as he accepted the award.


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Wednesday, February 27, 2013
Millions of people worldwide will recognize April as Parkinson's Awareness Month and supporters of Putting for Parkinson's are working hard to make their contribution on a local level.
Putting for Parkinson's started five years ago in hopes of helping find a cure for Parkinson's and to honor Coach Tim Touchberry, a long time teacher, coach, and athletic director in Dorchester Two schools who was diagnosed with Parkinson's disease in 2003. Money raised through the event goes to support research that is being done at The Murray Center at MUSC.
The 2013 Putting for Parkinson's is scheduled for April 27 at Legend Oaks Golf Club and event organizers are encouraging everyone to support the cause by becoming a sponsor, donating an auction or raffle item, golfing, attending the dinner and auction, and/or spreading the word.
Parkinson's disease is a movement disorder that is chronic and progressive. It affects many at both the local and national level.
Nearly one million Americans are living with Parkinson's.Approximately 60,000 Americans are diagnosed with Parkinson's disease each year, and this number does not reflect the thousands of cases that go undetected.Seven to 10 million people worldwide are estimated to be living with Parkinson's disease.Incidence of Parkinson's increases with age, but an estimated four percent of people with Parkinson's are diagnosed before the age of 50.Although promising research is being conducted at places like The Murray Center, there is currently no cure for or definitive cause of Parkinson's disease. That's why Putting for Parkinson's is continuing this April to raise awareness and funds for a cure.
For more information on this year's event, visit www.PuttingForParkinsons.com or contact email email@example.com.
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A disc storage system includes a rotating disc and a transducer. The transducer is carried on a slider which is supported by an armature. The armature is used to move the slider radially across the disc surface whereby information may be read from or written to the disc surface of the transducer. The slider includes an air bearing surface which faces the disc surface. As the disc rotates, the air bearing surface causes the slider to "fly" over the disc surface. Pads are provided on the air bearing surface to improve operational characteristics of the system. For example, the pads may be used to reduce the stiction or improve flying characteristics. Flying instabilities associated with the pads are addressed by a number of characteristics provided to the air bearing surface.
1. A disc drive storage system, comprising:
a rotating disc having a disc surface;
a transducer head adapted to read and write on the disc surface;
transducer circuitry coupled to the transducer head;
a slider having rails formed thereon and having an air bearing surface, the slider supporting the transducer head proximate the disc surface;
a plurality of pads carried on the rails having areas which contact the disc surface during contact start/stop (CSS), the plurality of pads causing instability and degraded flying characteristics of the slider; and
wherein the air bearing surface has a textured portion having at least a portion spaced from the plurality of pads and is disposed proximate a trailing edge of the slider to improve flying characteristics and stability of the slider and counter act degraded flying characteristics and instability caused by the plurality of pads.
2. The disc drive storage system of
3. The disc drive storage system of
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5. The disc drive storage system of
6. The disc drive storage system of
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9. The disc drive storage system of
10. The disc drive storage system of
11. The disc drive storage system of
12. The disc drive storage system of
13. The disc drive storage system of
14. The disc drive storage system of
15. The disc drive storage system of
16. The disc drive storage system of
17. The disc drive storage system of
18. A disc drive storage system, comprising:
a rotating disc having a disc surface;
a transducer head adapted to read and write on the disc surface;
transducer circuitry coupled to the transducer head;
a slider having a center island and rails formed thereon and having an air bearing surface, the slider supporting the transducer head proximate the disc surface;
a plurality of pads carried on the rails having areas which contact the disc surface during contact start/stop (CSS); and
wherein the air bearing surface has a textured portion having at least a portion disposed on the center island of the slider to reduce stiction when the slider is tipped.
19. The disc drive storage system of
20. The disc drive storage system of
21. The disc drive storage system of
22. The disc drive storage system of
23. The disc drive storage system of
24. The disc drive storage system of
25. The disc drive storage system of
26. The disc drive storage system of
27. The disc drive storage system of
28. The disc drive storage system of
29. The disc drive storage system of
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31. The disc drive storage system of
32. The disc drive storage system of
33. The disc drive storage system of
34. The disc drive storage system of
35. The disc drive storage system of
36. The disc drive storage system of
The present invention claims priority to Provisional Application Serial No. 60/093,745, filed Jul. 21, 1998, entitled "METHODS OF REDUCING STICTION ON SLIDERS WITH LANDING PADS DUE TO SUBSTRATE/DISK CONTACT"; and Provisional Application Serial No. 60/102,719, filed Sep. 28, 1998, entitled "SUPER SLIDER FOR IMPROVED TRIBOLOGICAL PERFORMANCE AND STABILITY".
The present invention relates to disc storage systems for storing information. More specifically, the present invention relates to sliders used in such systems.
Disc drives are used for storing information, typically as magnetically encoded data, and more recently as optically encoded data, on a disc surface. A transducing head is carried on a air-bearing slider that rides on a bearing of air above the disc surface as the disc rotates at high speed. In another technique, the slider contacts the disc surface with no air bearing interface such as is shown in U.S. Pat. Nos. 5,453,315 and 5,490,027. The head is then positioned radially over the disc to read back or write at a desired location. Benefits associated with an air bearing design are lost in such "contact" sliders.
In an air bearing design, the air bearing provides an interface between the slider and the disc which prevents damage to the disc over the life of the system, provides damping if the disc drive system undergoes shock due to external vibrations. The air bearing is also used to provide a desired spacing between the transducing element and the disc surface. A bias force is applied to the slider by a flexure armature in a direction toward the disc surface. This bias force is counteracted by lifting forces from the air bearing until an equilibrium is reached. The slider will contact the disc surface if the rotating speed of the disc is insufficient to cause the slider to "fly." This contact typically occurs during start up or shut down of the disc. If the slider contacts a region of the disc which carries data, the data may be lost and the disc permanently damaged.
In many disc drive systems, a lubricant is applied to the disc surface to reduce damage to the head and the disc surface during starting and stopping. Air or gas also acts as a lubricant. However, a phenomenon known as "stiction," which is caused by static friction and viscous shear forces, causes the slider to stick to the disc surface after periods of non use. The lubricant exacerbates the stiction problem. The stiction can damage the head or the disc when the slider is freed from the disc surface. Additionally, the spindle motor used to rotate the disc must provide sufficient torque to overcome the stiction.
One technique used to overcome the problem associated with stiction is to provide texturing to at least a portion of the disc surface. However, this reduces the effective recording area of the disc. Additionally, various attempts have been made to provide texturing on the air bearing surface of the slider. For example, U.S. Pat. Nos. 5,079,657 and 5,162,073 describes a technique for forming recesses in a slider surface. Another technique which is described in U.S. Pat. No. 5,418,667 includes providing large pads which provide a pitch to the slider to allow air flow between the air bearing surface and the disc.
A disc storage system includes a rotating disc and a transducer. The transducer is carried on a slider which is supported by an armature. The armature is used to move the slider radially across the disc surface whereby information may be read from or written to the disc surface of the transducer. The slider includes an air bearing surface which faces the disc surface. As the disc rotates, the air bearing surface causes the slider to "fly" over the disc surface. Pads are provided on the air bearing surface to improve operational characteristics of the system. For example, the pads may be used to reduce the stiction or improve flying characteristics. Flying instabilities associated with the pads are addressed by a number of characteristics which are provided to the air bearing surface.
FIG. 1 is a simplified diagram of a storage system in accordance with the present invention.
FIGS. 2A and 2B are bottom plan views of a slider including landing pads.
FIG. 3 is a graph of static friction versus contact start/stop (CSS) cycles.
FIG. 4 is a graph of static friction versus nominal area of contact.
FIG. 5 is a graph of friction versus roughness.
FIG. 6 is a graph showing friction, acceleration and velocity of a slider versus time.
FIGS. 7A, 7B and 7C are bottom plan view of sliders showing trenches formed near their trailing edge.
FIGS. 8A, 8B, 8C and 8D are bottom plan views of sliders showing various roughened areas.
FIG. 9A is a bottom plan view of a slider having micro pores formed therein.
FIG. 9B is a cross-sectional view taken along the line labeled 9B—9B of FIG. 9A showing the micro pores of FIG. 9A.
FIG. 9C is a plan view of micro pores connected by channels.
FIG. 10 is a bottom plan view of a slider which includes side kick features.
FIGS. 11A and 11B are side cross-sectional and plan views, respectively, of a landing pad with a trench.
FIG. 12A is a bottom plan view of a slider showing various features in accordance with the present invention to reduce the occurrence and the effects of tipping.
FIGS. 12B and 12C are side cross-sectional views taken along the lines labeled 12B—12B of FIG. 12A showing portions of a rail of the slider of FIG. 12A.
FIGS. 13, 14, 15, 16 and 17 are bottom plan views of sliders showing various embodiments of the present invention.
FIG. 18 is a perspective view showing a center island of a slider which includes trenches formed therein.
FIG. 1 is a top view of a disc drive 10 including a slider in accordance with the present invention. Disc drive 10 includes a magnetic disc 12 mounted for rotational movement about and axis defined by spindle 14 within housing 16. Disc drive 10 also includes an actuator 18 mounted to a base plate 20 of housing 16 and pivotally moveable relative to disc 14 about axis 22. A cover 24 covers a portion of actuator 18. Drive controller 26 is coupled to actuator 18. In the preferred embodiment, drive controller 26 is either mountable within disc drive 10, or is located outside of disc drive 10 with suitable connection to actuator 18. Actuator 18, includes an actuator arm assembly 28, a rigid support member 30, and a head gimbal assembly 32. Head gimbal assembly 32 includes a load beam or flexure arm 34 coupled to rigid member 30, and a slider 36 coupled by a gimbal (not shown) to load beam 34. Slider 36 operates in accordance with the embodiments set forth herein and supports a transducer for reading information from and encoding information on disc 12.
During operation, drive controller 26 receives position information indicating a portion of disc 12 to be accessed. Drive controller 26 receives the position information from an operator, from a host computer, or from another suitable controller. Based on the position information, drive controller 26 provides a position signal to actuator 18. The position signal causes actuator 18 to pivot about axis 22. This, in turn, causes actuator 18 to pivot about axis 22. This, in turn, causes slider 36 (and consequently the transducer mounted on slider 36) to move radially over the surface of disc 12 in a generally arcuaic path indicated by arrow 38. Drive controller 26 and actuator 18 operate in a known closed loop, negative feedback manner so that the transducer carried by slider 36 is positioned over the desired portion of disc 12. Once the transducer is appropriately positioned, drive controller 26 then executes a desired read or write operation.
Recording density can be increased by reducing the fly height of slider 36. Close proximity of slider 36 with disc 12 allows greater accuracy in reading and writing information onto disc 12.
Stiction and fly/stiction are two major phenomena that impair the use of ultra-low flying recording heads to increase recording areal density. The solution to these problems has been to generate, in a controlled fashion, some asperities, or texture, on the media surface to reduce the area of contact at the head-media interface. The presence of these asperities on the media surface, although they can be confined to only within a small dedicated zone (i.e., a "landing zone"), enhances the chance of head-media contact during operation and thereby sets the limit to the true attainment of ultra-low flying. In most cases, due to the shape of the asperity, the nature of contact is called Hertzian contact, in which elastic deformation can occur locally. Consequently, the number of asperities on the media surface to support the head cannot be arbitrarily reduced, otherwise the interface will collapse leading to excessive stiction. In addition, this type of contact is prone to collapsing when an excessive amount of liquid lubricants are present in the interface. For example, the lubricant applied on the media to prevent wear during head-disc contact, as well as other outgassing materials from various drive components, may accumulate on the heads, and transfer to the interface thereby leading to excessive fly/stiction.
One technique to address these issues is the use of small column-like texture features, i.e., landing pads, on the air bearing surface of a flying head to control stiction. Sliders with such landing pads can be used on substantially smooth discs. The use of such pad is described in U.S. patent application Ser. No. 09/029,276, filed Dec. 9, 1998, entitled "SLIDER FOR DISC STORAGE SYSTEM" which is incorporated herein by reference.
FIGS. 2A and 2B are bottom plan views of sliders 200. Similar elements have been numbered the same. Slider 200 includes a slider body 202 having rails 204 and 206 extending between a leading edge 208 and a trailing edge 210. A center island 212 is positioned on trailing edge 210. In slider 200 of FIG. 2A includes four pads 214 positioned on rails 204 and 206. In the embodiment of FIG. 2B, slider 200 includes multiple pads 216 positioned on rails 204 and 206.
The use of the pads on the air bearing surface of the slider reduces the area of contact and thus reduces the stiction/friction when contacting a very smooth storage medium. Typically, the landing pads have heights on the order to 200 nm to 700 nm and are attached to the air bearing surface shown generally at 218. To avoid contact during flying, the pads are typically positioned 254 μm away from trailing edge 210. However, this geometry creates instabilities under both dynamic and static conditions. For example, under static conditions when the slider stops on the disc it has a tendency to tip due to back rotation of the motor which drive spindle 14. This causes contact of the trailing edge 210 and wear of the rear pads occurs. Further, during wear of the slider pads, the slider body may tip.
An approximate calculation shows that when the slider tips backwards, the area of contact increases by approximately an order of magnitude and thus the friction also increases by an order of magnitude. This pseudo-linear dependence of friction to the nominal area of contact has been observed experimentally as illustrated in FIG. 2 which is a graph of static friction versus contact start/stop (CSS). This is also predicted using a friction model as described in Polycarpou, AA., Etison, I., 1998, "Static Friction of Contacting Real Surfaces in the Presence of Sub-Boundary Lubrication," ASME Journal of Tribology, Vol. 120, pp. 296-303. The prediction of this model is illustrated in FIG. 4 which is a graph of static friction versus nominal area of contact. This model is an alternative to meniscus stiction models and is more accurate for strong lubricant solid bond, very thin lubricants typically used at the head/disc interface. The static friction coefficient μ is written as:
where Q, F, P and FS are the friction, preload, contact and adhesion forces, respectively. The surfaces are modeled with a surface roughness model that allows for elastic-plastic deformation of the asperities. The model depends on the preload and nominal area contact, surface roughness (standard deviation of asperity heights related to Ra, radius of curvature of asperity heights, areal density of asperities, and the distribution of asperity heights. It also depends on the material properties (hardness, elastic modulus of elasticity, and Poisson's ratio), and the lubricant properties of energy of adhesion (surface free energy), intermolecular spacing, and the lubricant thickness.
The friction is strongly and non-linearly dependent upon the roughness, as observed experimentally and also as predicted by the above model. FIG. 5 is a graph of friction versus the roughness parameter σ/R which shows the effect of roughness on friction for rough, smooth and very smooth surfaces.
Another phenomenon that may take place during the tipping of a slider is the migration of the mobile lubricant present at the interface. This can form large menisci and thereby increase stiction. Another phenomenon is the contact of the outer radius and/or the inner radius of the slider either during flying or during static conditions. The net effect of this contact is an increase in the contact area, and thereby an increase in the stiction/friction. Such large increases in stiction are catastrophic for the head/disc interface causing the head to stick and crash on the media.
Both dynamic and static interaction of the slider and the media cause the unstable behavior and tipping of the slider. In dynamic interaction, when the slider comes to a stop and transitions from sliding to sticking, the friction force (or tangential force) typically oscillates at a system resonance indicating that the slider is experiencing some form of rocking and translational motion. This is shown graphically in FIG. 6. In FIG. 6, the dotted line is the velocity as the slider moves from sliding to sticking (0 velocity). The thick solid line is a graph of the friction force showing that as the velocity goes to zero, the friction also drops to zero and moves through negative values thereby fluctuating. The thinner solid line is a graph of tangential acceleration of the slider which indicates that the transition from sliding to sticking is abrupt and the slider oscillates after it comes to a stop. During such oscillations, the slider air bearing surface and the center pad will contact the media. Static geometrical analysis indicates that even 500 microradians of tilt of the slider is sufficient to cause contact at the trailing edge of the slider.
Further, typically drive spindles in disc drive systems experience a backlash when coming to a stop and before they start to spin. As these backward motions are usually very small, and because the friction at the landing pads is sufficiently high, sliding does not occur in the slider tips.
The increased area of contact (in addition to the area from the landing pad) and not the increased friction may also be caused from wearing of the landing pads or from built in variations from the geometry of the slider such as crown and cross curved.
Thus, although such slider designs have reduced stiction, the complex nature of the air bearing surface including landing pads, curvatures, preload offsets, and stringent flying requirements such as pitch, roll, etc. lead to instabilities under both static and dynamic conditions or during the wearing in of the pads.
One technique used to reduce the area of possible contact and prevent the migration of mobile lubricants is the use of trenches as illustrated in FIGS. 7A, 7B and 7C. Sliders 220, 222 and 224 include trenches 226, 228 and 230, respectively which are positioned closer to the trailing edge of the slider. The trenches may be in any direction including horizontal, vertical or crosswise as illustrated in FIG. 7B. All three designs achieve a reduction in stiction values. However, the reduction in stiction is only about 50%, from 30 grams to between about 10 and 15 grams. Additionally, significant wear is observed near the trenches.
Another technique to reduce slider tipping is by "roughening" portions of the air bearing surface. Any portion of the air bearing surface including the center pad and side rails can be roughened using appropriate techniques. In one technique, the surface is coated with diamond-like carbon (DLC) for corrosion protection and the TiC is chemically etched. This can increase the Ra value of the air bearing surface from 2 nm to 9 nm. Further roughening can cause pitting of the air bearing surface. The roughening decreases friction and the contact area is reduced due to the pitting. These pits act as potential locations for storing wear debris and they also increase the positive pressure into additional aerodynamic effects. Another roughening technique is a short duration ion milling. After the air bearing surface has been lapped, an ion beam is applied to achieve a milling depth of around 0.3 μm providing an Ra value change from 1 nm to between 10 and 50 nm. Assuming a square root relationship between ion milling time and milling depth, a three minute ion milling time produces a roughness Ra value of 6.0 nm.
FIGS. 8A, 8B, 8C and 8D are bottom plan views of sliders 240, 242, 244 and 246, respectively, showing various "roughened" areas. In FIG. 8A, a roughened area 250 is positioned near the trailing edge of the slider. The majority of rails 252 are not roughened and carry landing pads 254. In FIG. 8B, rails 256 and center pad 258 are roughened everywhere. However, in FIG. 8C, only center pad 260 has been roughened. FIG. 8D illustrates a slider 246 in which roughened areas 262 are positioned near landing pads 264. Additionally, center island 266 also contains a roughened region 262. The roughened regions are merely provided as examples for illustrating the invention.
In addition to roughening areas of the air bearing surface, small holes, or "micro pores" can be used on the surface. FIG. 9A is a bottom plan view of a slider 270 including micro pores 272 carried on side rails and the center island of the slider 270. Pads 274 are also carried on the rails. The micro pores reduce the area of contact and thus reduce the stiction and friction. Further, the micro pores have aerodynamic properties which contribute to the lift of the air bearing surface. This reduces contact force and thereby reduces friction and wear. The shape and size of micro pores can vary as desired to achieve optimal load carrying capacities. Example shapes of the micro pores are illustrated in the inset 276. FIG. 9B is a side cross-sectional view of a portion of the side rail of FIG. 9A taken along the line 9B—9B. The cross-sectional shape of the micro pores can vary as desired. Several different shapes are illustrated in inset 278. FIG. 9C shows a close up of a portion of the air bearing surface of the slider 270 of FIG. 9A. In the embodiment of FIG. 9C, the micro pores are connected by channels 280 which reduces the trapping of any lubricant or debris in the micro pores. This reduces the migration of lubricant which may take place during stopping of the slider which is known to lead to increased friction.
FIG. 10 is a bottom plan view of slider 290 in which "side kicks" 292 are positioned on center island 296. The side kicks 292 are small pads, for example, small diamond-like carbon bumps which reduce tipping of the slider 290. However, if the slider is not flying optimally due to high roll or if the slider is flying too low, or if the geometry of the slider is incorrect such as the crown or camber being out of specification, the side kick pads 292 are quickly worn off and the very smooth air bearing surface comes into direct contact with the disc surface leading to high stiction.
FIG. 11A is a side cross-sectional view and FIG. 11B is a bottom plan view showing pad 298 with a moat or a trench 300 extending around the pad 298. The moat 300 acts to reduce stiction by reducing the gross menisci which is formed around pad 298.
Another technique to reduce stiction is to provide the slider with a high crown. For example, crowns greater than 1 μin and preferably about 1.5 μin offer reduced stiction, even if the slider tips. This reduction in stiction is due to the smaller area that contacts the media.
In one aspect of the present invention, some or all of the aforementioned techniques are combined to provide a slider with superior tribological properties which is substantially insensitive to geometrical variations, contaminants, lube thickness variation and media type for both textured or polished media. Preferably, the slider is insensitive to very smooth media (Ra less than 5 Å) which is particularly desirable for high aerial recording densities and low fly heights.
In FIG. 12A a slider 320 which includes diamond-like carbon pads 322 carried on rail 324. Some or all of the pads 322 include trenches 325 which surround their base to reduce meniscus formation. The number of landing pads and their locations can vary depending upon the specific air bearings type and shape, the geometry of the slider and the load that the slider needs to carry. The diamond-like carbon pads are preferably spaced away from the trailing edge of the slider such that there is no interference or contact with the media. However, this effect increases the propensity of slider 320 for tipping, especially during starting and stopping of the slider. When slider 320 tips, a large area of the smooth air bearing surface and center pad 328 come into contact with the smooth media causing a significant increase in the stiction due to the increase in the adhesive and meniscus forces. Prolonged high stiction can lead to excessive wear of the pads and cause crashes of slider 320. In order to reduce tipping, side kicks 330 made of shorter diamond-like carbon pads (between about 100 and about 300 Å) are placed on center rail 328 to reduce slider tipping during start up and stopping. Further, slider 320 has a relatively large crown which minimizes the effects of tipping by preventing a large contact area between slider 320 and media surface. In the embodiment shown, there are two side kicks 330. Additionally, the shape of side kicks 330 can be selected as appropriate for various air bearing designs such as using round pads, oval pads or long thin pads which may provide advantageous air bearing effects. Additionally, trenches 332 are provided on center pads 328 to further reduce the contact area should tipping occur. Trenches 332 also provide paths for drainage of lubricant such that lubricant does not concentrate on center island 328 which could cause high stiction. Roughened areas 334 are provided near the trailing edge of rails 324 of slider 320 to prevent high stiction. FIG. 12B is a cross-sectional view of slider 320 taken along the line labeled 12B—12B. As illustrated in FIG. 12B, the mean plane of the roughened portion 334 can be parallel with the plane of the smooth portion of rail 324. In another embodiment as illustrated in FIG. 12C, the mean plane of roughened area 334 is recessed from the rest of rail 324. This can be achieved through ion milling or etching techniques as are known in the art. By recessing the roughened areas 334, greater distances provided between the trailing edge of slider 320 and the media to further reduce the effects of tipping. This also allows reduced flying which will increase the control or stiffness of the air bearing which is particularly useful in proximity recording application.
FIG. 13 is a bottom plan view of a slider 340 in which the entire surface of rails 342 is roughened as is center island 344. Small kick pads 346 are defined at the trailing edge of rails 342 and on center island 344.
FIG. 14 is a bottom plan view of a slider 350 having short rails 352 and a center island 254 which is substantially entirely roughened. Trenches 356 are also defined in center island 354. In the embodiment of FIG. 15, a slider 360 is shown in which a center island 362 positioned near the leading edge of the slider carries a bump, such as a DLC bump 364. Rails 366 include skids or bumps 368. All or part of the rails 366 is roughened as illustrated in FIG. 15. Further, trenches 370 are formed in rails 366. In the embodiment shown, the trenches are positioned near the trailing edge of the slider and extend in a generally diagonal direction relative to the direction of sliding.
In FIG. 16, a slider 380 is shown in which leading edge pads 382 have a height which is greater than trailing edge pads 384. Additionally, trenches 386 are provided on the center island. The short trailing edge pads act as multiple side kick features.
FIG. 17 is a bottom plan view of a slider 390 using DLC bumps 392 and side kick features 394. In the embodiment shown, bumps 392 cover substantially the entire air bearing surface. This is due to the particular masking technique used to fabricate bumps 392. The bumps in the recessed portions of the air bearing surface generally have no effect and can be eliminated. Roughened portions 398 are provided at the trailing edge of rails 400. Preferably, the air bearing surface of slider 390 has a high crown. FIG. 18 is a perspective view of a portion of a slider showing center island 410 and the trailing edge of rails 412. Center island 410 includes vertical trenches 414 formed therein.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. In general, the pads may be placed along any protruding portion of the air bearing surface such as the side rails, a center rail, a center island, etc. In general, the present invention includes all of the various sizes, shapes, heights, placings, configurations, densities, etc. of the pads set forth herein. Such pads may be made in accordance with any of the processes set forth herein or may be fabricated using other processes as desired. Similarly, the specific process herein are not limited to fabrication of those pads which have been specifically set forth herein. The invention may be used with any type of transducing element including inductive, magnetoresistive and optical elements. In general, in these designs the pads only contact the disc surface during CSS and do not contact the disc surface during normal flying. As used herein, a "textured portion" or "texture" means any configuration of the air bearing surface in which features have been added in order to have a desired aerodynamic effect.
Referenziert von
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Serving Size 1 Capsule (325 mg)
Servings: 120
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Each capsule contains: A vegetarian capsule made of water and hypromellose (USP).
Suggested Use: Take 1 capsule in early a.m. and 1 capsule in late p.m. with a glass of warm water. For extra strength: take an additional capsule in mid-a.m. and in the mid-p.m. Eventually reduce to taking 1 capsule a day. Drink 4-6 glasses of water daily while taking Pro•Essence.
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Sex and Race Why White and Black Mix in Spite of Opposition
Of the trilogy, this one was especially difficult to put down because the content is quite riveting. It was amazing how this reporter, researcher, historian and anthropologist could go around the world and find out information in the most minute detail. However, you have modern scholars who cannot decipher many of the historical texts with any type of accuracy and without bias. J.A. Rogers set out to answer most of your questions on the social and sexual issues between Africans and Europeans. In addition, there is the "Shock" factor and history that you just may not get anywhere else, except with exceptional authors like this one'.. And just like the previous two volumes to make his case, he has great black and white photos and all of the references to validate his point.
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