of potential respiratory dysfunction has been investigated but findings suggest it is of limited value. Respiratory rate is a clear indicator of acidotic states, as the main function of respiration is removal of CO2 leaving bicarbonate base in circulation. Blood pressure Blood pressure is recorded as two readings: a higher systolic pressure, which occurs during the maximal contraction of the heart, and the lower diastolic or resting pressure. In adults, a normal blood pressure is 120/80, with 120 being the systolic and 80 being the diastolic reading. Usually, the blood pressure is read from the left arm unless there is some damage to the arm. The difference between the systolic and diastolic pressure is called the pulse pressure. The measurement of these pressures is now usually done with an aneroid or electronic sphygmomanometer. The classic measurement device is a mercury sphygmomanometer, using a column of mercury measured off in millimeters. In the United States and UK, the common form is millimeters of mercury, while elsewhere SI units of pressure are used. There is no natural 'normal' value for blood pressure, but rather a range of values that on increasing are associated with increased risks. The guideline acceptable reading also takes into account other co-factors for disease. Therefore, elevated blood pressure (hypertension) is variously defined when the systolic number is persistently over 140–160 mmHg. Low blood pressure is hypotension. Blood pressures are also taken at other portions of the extremities. These pressures are called segmental blood pressures and are used to evaluate blockage or arterial occlusion in a limb (see Ankle brachial pressure index). Other signs In the U.S., in addition to the above four, many providers are required or encouraged by government technology-in-medicine laws to record the patient's height, weight, and body mass index. In contrast to the traditional vital signs, these measurements are not useful for assessing acute changes in state because of the rate at which they change; however, they are useful for assessing the impact of prolonged illness or chronic health problems. The definition of vital signs may also vary with the setting of the assessment. Emergency medical technicians (EMTs), in particular, are taught to measure the vital signs of respiration, pulse, skin, pupils, and blood pressure as "the 5 vital signs" in a non-hospital setting. Fifth vital signs The "fifth vital sign" may refer to a few different parameters. Pain is considered a standard fifth vital