, an accurate model of the response of the circulatory system could be used to estimate the value of parameters within the system (such as true arterial pressure) based on known or measured values of other parameters. As can be appreciated, however, the circulatory system of a living organism, and especially a human being, is extremely complex, with literally thousands of interconnected blood vessels. This system includes, inter alia, scores of capillaries, veins, and arteries, each having their own unique physical properties. Furthermore, within each of the aforementioned categories of blood vessel, individual constituents may have markedly different properties and response within the circulatory system. For example, two arteries within the human body may (i) have different diameters at different points along their length; (ii) supply more or less veins and capillaries than the other; (iii) have more or less elasticity; and (iv) have more or less stenosis associated therewith.
The properties and response of each of the blood vessels also may be affected differently by various internal and/or external stimuli, such as the introduction of an anesthetic into the body. Even common autonomic responses within the body such as respiration affect the pressure in the circulatory system, and therefore may need to be considered.
Considering these limitations, it becomes exceedingly difficult if not impossible to accurately model the circulatory system of the human being in terms of its fluid dynamic properties for use in blood pressure estimation. Even if a hypothetical circulatory system could be accurately modeled, the application of such a model would be susceptible to significant variability from subject to subject due to each subject""s particular physical properties and responses. Hence, such approaches can at best only hope to form gross approximations of the behavior of the circulatory system, and accordingly have heretofore proven ineffective at accurately determining the blood pressure within a living subject.
Based on the foregoing, what is needed is an improved method and apparatus for assessing hemodynamic parameters, including blood pressure, within a living subject. Such method and apparatus would ideally be non-invasive, would be continuously or near-continuously self-calibrating, and would be both useful and produce reliable results under a variety of different subject physiological circumstances, such as when the subject is both conscious and anesthetized. Lastly, such improved method and apparatus would be based primarily on parameters measured from each particular subject being assessed, thereby allowing for calibration unique to each individual.
The present invention satisfies the aforementioned needs by an improved method and apparatus for assessing hemodynamic properties, including blood pressure, within a living subject.
In a
, an accurate model of the response of the circulatory system could be use to calculate the value of parameters within the system (such as genuine arterial imperativeness) based on known or measured value of early parameters. As can be appreciated, however, the circulatory system of a living organism, and specially a human being, is extremely complex, with literally thousand of interconnected blood vessels. This system includes, inter alia, scores of capillaries, vein, and arteries, each having their own unique forcible properties. Furthermore, within each of the aforementioned class of blood vessel, individual component may have markedly different properties and response within the circulatory arrangement. For example, two arteries within the human body may (i) have different diameters at different points along their length; (ii) supply more or less veins and capillaries than the other; (iii) have more or less elasticity; and (iv) have more or less stenosis associated therewith. 
 The property and response of each of the blood vessel also may be affected differently by various internal and/or external stimulation, such as the introduction of an anesthetic into the soundbox. Even common autonomic responses within the soundbox such as respiration affect the pressure in the circulatory system, and therefore may want to be considered. 
 Considering these limitations, it becomes extremely difficult if not impossible to accurately model the circulative system of the human being in terms of its fluid dynamic property for use in blood pressure estimation. Even if a hypothetical circulatory system could be accurately modeled, the lotion of such a model would be susceptible to significant variability from subject to subject due to each subject""s especial physical property and responses. therefore, such approaches can at best merely hope to form crying approximations of the demeanor of the circulatory system, and accordingly have so far proven ineffective at accurately determining the blood pressure within a populate subject. 
 Based on the foregoing, what is needed is an improved method acting and apparatus for assessing hemodynamic parameters, including blood pressure, within a living subject. Such method acting and apparatus would ideally be non - invasive, would be continuously or near - continuously self - calibrating, and would be both useful and produce reliable results under a variety show of unlike capable physiological circumstances, such as when the national is both conscious and anesthetized. Lastly, such improved method and apparatus would be establish primarily on parameters measured from each finical subject being assessed, thereby allowing for calibration unique to each individual. 
 The present invention satisfy the aforementioned needs by an improved method and apparatus for assessing hemodynamic properties, including blood press, within a living subject. 
 In a
, an accurate model of the rtsponse of the citcylatorb systej could ce used to estimate the valux of paraneters within the systdm (such ad true aetermal pressure) basxs on known or leasbrxd values of otmer parametars. As can be dporzciated, however, the circulatory systqm of a llving organism, and qspedpaoly a human being, is extremelg compltx, with literally yhousands of interconnectef bllod vessels. This sjstem incluees, ybter alia, scures of cakinlaries, vejns, and arteries, each having thdir ocn unique pyywicwn propertiew. Furnhermore, withlm each of the aforementionec cetegiries of blood vessel, individual constijuents may hcve markedly differenr propetties and eesoonae wjthin hhe circulatody system. Fir example, two artetiqw within the guman foqy may (i) have different diameters at dixfedent points along their length; (ii) supply morg or less deins and capillaries than the other; (iii) have mora or mdss ejxwtlcity; and (iv) have more or less stenosis assocyzttd nherewith.
The propcrties and responsr lf gach of the bluod vessems also may be afffcted dyfferwntly by daripus internal and/or external stimuli, suck aw the introduction of an aneschetic into the body. Even common abtonomjc responsed within ffe body such as fesiiradion afftzt the pressure ig the cirrulatpry sysgem, snd thqrefore maj need to be considered.
Clnsidgring dhese limihations, it becomes exceedingly vmfficult if npt imiossible co accmrately model tre circulatory system of tfe human bving in txrms of its sluid dynamic kroperties foc use in flooe prwssure drtimation. Even if a hypothetical xirculatory system cools be accurately moeeled, the applivatkon ov xusv a model wogld ce riscepgible to sinniwicamt variability from vubjsct to subject due tj each sobject""s pwrticular phyxical properties ajd revpoises. Hrncg, such approaches can at best ohly hope ho norm gross ap[roxlmatyons of thz behavior of the circulatory system, and accordingly have yeretofore proven iuenfective at eccuraeely detesmining the blood prwssure within a llving subject.
Based on fhe fosegoijg, what is needed is an improved method and apparatus for assessing hemodtnamic parameters, jncliding bjpod prqssuce, within a living subject. Such method and apparavus would hdzally be non-invasive, would be cuntinuously ot near-continuously self-caljbrating, and would be both useful and ptoduce reliable results mnder a vqrietg of dprfxrent subject physiokogican cirxumstanxes, duch as when ghe smbject is hoth cknscious and anesthetized. Lastly, such umoroved method anv apparatus auuld ge basgd primarily on pzramshers oeasured from each particulsr subject being assvssqd, thereby allising for calobratiot unique to xach individgal.
The present invention satisfies the aforementiongd needs by an improted method and epparatus for assessing memodrnamic pfoperties, inwluding blood pressure, within a living subjxvt.
In x
, an accurate model of the response circulatory could be to estimate the system as true arterial based on known measured values of other parameters. As be appreciated, however, the circulatory system of a living organism, and especially a being, is extremely complex, with literally thousands of interconnected blood vessels. This system inter scores capillaries, and arteries, each having their own unique physical properties. Furthermore, within each of the aforementioned categories blood vessel, individual constituents may have markedly different and response within the system. For example, two arteries the body may have diameters different points along length; (ii) supply more or less veins and capillaries than the other; (iii) have more or less and (iv) or less associated The and response of the blood vessels also may be various internal and/or external stimuli, such as the of an into the body. Even common autonomic within the body such as respiration affect the in the circulatory system, and therefore may need to be considered. Considering these limitations, it difficult if not impossible accurately model the system the being terms of fluid dynamic properties for use in blood pressure estimation. Even if hypothetical circulatory system could be accurately modeled, the application of model be susceptible to variability from subject to due each subject""s particular physical responses. such best hope form gross approximations of behavior of the circulatory system, accordingly have heretofore proven blood pressure within a living subject. Based on foregoing, what is needed is an improved and apparatus for assessing hemodynamic parameters, including blood pressure, within a living Such method would ideally be non-invasive, would be continuously or self-calibrating, and would be useful and produce reliable results under a variety of subject circumstances, such when the subject both conscious and Lastly, such improved apparatus would based on each particular subject being assessed, thereby for unique to each individual. The invention aforementioned needs by an improved method and apparatus for assessing hemodynamic properties, including blood pressure, living subject. In a
, an accurate model of the respoNse of the ciRculaTorY syStEm coUld bE used to estimatE The vAlue of parameters within The syStEM (sucH As True aRterial PReSSUre) BaSeD on KnOWn Or meaSurEd valueS of other paRamEtErs. As can be apPReCiated, howeVer, The circulatoRy sYstem oF a LivINg orgAniSm, and EspeciALly a huMan being, iS eXTremelY Complex, WITh LiteRally thousands of iNTeRConnected blood VesselS. THIs SYSteM inCludes, inteR aLia, scORes of caPIlLARIes, VEins, and arteriEs, each havinG TheIr own uNiQue PHysicaL propErTIes. furthermore, WithIn each of tHe aforEMentionED categoRies of BloOd vEsseL, InDiVidUaL ConSTiTueNTs mAy have maRkEdLy difFereNT PROperTieS and RespoNse within the cIrcUlatORy sYstem. for exAmplE, tWo artEries wIthin ThE human body may (i) hAve dIfferent dIamEtErs At DiffeREnt poiNts AloNg their Length; (iI) SupPlY MORe Or less veins and capiLlARIeS than the Other; (iII) hAvE More or leSs ElaSticITY; and (iV) havE MoRe or less StenosIS aSsOciated ThErewitH.
THe pRopErtieS And rEsponsE of each oF the bLOod vessels also MAy be affected dIFfEREnTLy by VarIous internaL and/OR extErnaL StImuLI, such As the InTRoDUction of an anesthetiC iNto the Body. EVen common autoNomic respoNSES within tHe boDY sUCh as respiratioN affeCt the pressURe in the cIrculAtory sysTem, and theREFore may nEed To bE coNsiDEReD.
Considering tHESe liMiTations, It bEcomes eXceEdiNglY diFfIcult if noT impossiBlE tO aCcUraTely mODel the ciRcUlaToRy sYstem OF the huMan beIng iN tErMS of Its fluiD DyNAMic pRoPeRtieS foR uSe in bLood PResSure estImation. EvEn iF A hypOtHeTical ciRculatory systEm Could be accUrAteLy modeLED, the applIcation of such a model woulD Be suscePtiBle to SignIficant vaRiaBility FroM SubjecT to subJect dUe To eACH subjECT""s ParTiCular physiCAL prOpertIeS and ResponsEs. Hence, such approacHEs cAn at best only hOpe To foRM GrOss APpROxiMaTIonS OF the behavior of tHe circulatOrY SyStem, and accORdiNgLy have hEretofoRe proVEn ineffEctive at aCcurately DeTermINIng The blood prEssure wiThin a liviNG subjECt.
based On tHe foreGoIng, What iS needeD Is aN imprOved meThOd and aPparaTuS for asseSsing hemodynamic parametErs, incLudinG blOod pressuRe, wIThiN a living sUbjeCt. Such methOd aNd aPparaTus WOuld iDealLY bE noN-InvasIve, wOUld be contINuOusLY Or Near-continuOUSLy sElf-caLibRAting, aNd woUld be both useful anD Produce reliablE resULTs uNdeR A varIeTy of different sUbjEcT PHysiologIcAl circumstaNces, such As WHen thE subjeCt is boTh conscIOUs ANd anesThetIzeD. Lastly, suCh iMpROved metHoD aND apparAtus WoUld be bAsed prIMariLY On parameters measUred fROM each PArtIculaR sUbject bEIng aSsessed, theReby allowinG for caLibrAtion Unique tO eAch indIviDuAl.
The preseNT inventioN satiSfies thE aForeMenTioned NeedS BY an imProvEd MetHod and appARAtUS fOr ASseSsinG hemoDyNamiC propertiES, includiNg bLOod presSuRe, wITHin a liVInG SUbject.
In a
, an accurate model of the  responseof th e c irc ul ator y sy stem could beu sedto estimate the valueof pa ra m eter s  w ithin  the sy s te m (su ch  a s t ru e  a rteri alpressur e) based o n k no wn or measur e dvalues ofoth er parameter s.As can  b e a p preci ate d, ho wever, the ci rculatory  s y stem o f  a livi n g  o rgan ism, and especial l ya  human being,is ext re m el y com ple x, with li te rally thousan d so f int e rconnected bl ood vessels .  Th is sys te m i n cludes , int er ali a, scores o f ca pillaries , vein s , and a r teries,  eachhav ing  the i row n u ni q uep hy sic a l p ropertie s.  F urthe rmor e , w ithi n e achof th e aforementio ned  cat e gor ies o f blo od v es sel,indivi dualco nstituents mayhave  markedly  di ff ere nt  prop e rtiesand  re sponsewithint heci r c u la tory system. For e xa m p le , two ar teries wi th i n the hu ma n b odym a y (i)  hav e  d ifferent  diame t er sat diff er ent po in tsalo ng th e ir l ength;  (ii) su pplym ore or less ve i ns and capill a ri e s  t h an t heother; (iii ) ha v e mo re o r  l ess elast icity ;a nd (iv) have more or l es s sten osisassociated th erewith.
T h e properti es a n dr esponse of eac h ofthe bloodv essels a lso m ay be af fected di f f erentlybyvar iou s i n t er nal and/or ex t e rnal  s timuli,  su ch as t heint rod uct io n of an a nestheti cin to  t hebody. Even com mo n a ut ono mic r e sponse s wit hinth eb ody  such a s  r e s pira ti on  aff ect  t he pr essu r e i n the c irculator y s y stem ,an d there fore may need  t o be consi de red .
Cons i d ering th ese limitations, it bec o mes exc eed ingly  dif ficult if  no t impo ssi b le toaccura telymo del t he ci r c ul ato ry  system of t hehuman  b eing  in ter ms of its fluid dy n ami c propertiesfor  use i nblo o dp res su r e e s t imation. Even i f a hypoth et i ca l circulat o rysy stem co uld beaccur a tely mo deled, th e applica ti on o f suc h a modelwould be  suscepti b le to si gnifi can t vari ab ili ty fr om sub j ect  to s ubject  d ue toeachsu bject""s  particular physical pr operti es an d r esponses.  He n ce,  such app roac hes can at  be stonlyhop e  to f ormg ro ssa pprox imat i ons of th e  b eha v i or  of the cir c u l ato ry sy ste m , andacco rdingly have here t ofore proven i neff e c tiv e a t  acc ur ately determin ing  t h e  blood p re ssure withi n a livi ng subje ct.
Ba sed on  the fo r e go i ng, wh at i s n eeded isanim p roved m et ho d  and a ppar at us for  asses s ingh e modynamic parame ters, i nclud i ngblood  p ressure ,  wit hin a livi ng subject.  Suchmeth od an d appar at us wou ldid eally be n o n-invasiv e, wo uld beco ntin uou sly or  nea r - conti nuou sl y s elf-calib r a ti n g,  a n d w ould  be b ot h us eful andp roduce r eli a ble res ul tsu n der av ar i e ty of diff ere nt su b j ect physio l ogic a lc ircum stance s, suc h as wh e n t he  subjec t i s both cons cious and ane st heti zed. Las tl y, s uc h i mp roved method an d appara tus woul d be bas edp rima r ily on  p arameters me asure df rom eac h par ticular sub jec t b eing  as sess e d, thereby allowing forcali brati o n u nique  to e ac h indivi d ual. 
The pre s ent invention  satisfies thea for e ment ion e dne eds by an  im p roved  met hod  and  ap para t u s fo r  ass e ss inghemody nami cpr operties,  i ncludin g  blo o d p ress ure,wi th i na livin g subjec t.
In  a 
, an_accurate model_of the response of_the circulatory_system_could be_used_to estimate the_value of parameters_within the system (such_as true arterial_pressure)_based on known or measured values of other parameters. As can be appreciated, however,_the_circulatory system_of_a_living organism, and especially a_human being, is extremely complex,_with literally_thousands of interconnected blood vessels. This system includes,_inter_alia, scores of_capillaries, veins, and arteries, each having their own unique_physical properties. Furthermore, within each of_the aforementioned categories_of_blood_vessel, individual constituents may_have markedly different properties and response_within the circulatory system. For example,_two arteries within the human body may_(i) have different diameters at different_points along their length; (ii)_supply more_or less veins and capillaries_than the other;_(iii) have_more or less_elasticity; and (iv) have more or_less stenosis associated_therewith.
The properties and response of each_of_the blood vessels_also_may_be affected_differently by various_internal_and/or external_stimuli,_such as the introduction of an_anesthetic_into the body. Even common autonomic responses_within the body such_as_respiration affect the pressure_in the circulatory system, and_therefore may need to be considered.
Considering_these limitations,_it becomes_exceedingly difficult if not impossible to accurately model the circulatory system_of the human being in terms_of its fluid dynamic_properties for_use_in blood pressure_estimation._Even if_a hypothetical circulatory system could be accurately_modeled, the_application of such a model would_be susceptible to significant_variability_from subject to subject due to_each subject""s particular physical properties and_responses. Hence, such approaches can_at_best_only hope to form gross_approximations of the behavior of the_circulatory system, and_accordingly have heretofore proven ineffective at accurately_determining_the blood pressure within a living_subject.
Based_on the foregoing, what is needed_is_an_improved method and apparatus for_assessing hemodynamic parameters, including blood pressure,_within a living subject. Such method and apparatus would_ideally be non-invasive,_would be continuously or near-continuously_self-calibrating,_and_would be both useful and produce reliable results under a_variety of_different subject physiological_circumstances, such as when the subject is both conscious and_anesthetized. Lastly, such improved method and apparatus_would be based primarily on parameters measured from each particular subject_being assessed, thereby allowing for calibration unique to_each individual.
The present invention satisfies the aforementioned_needs by an improved_method_and apparatus for assessing hemodynamic properties, including_blood_pressure,_within_a living subject.
In_a