Sphygmomanometer
A sphygmomanometer is an apparatus for measuring the blood pressure. The human body performs metabolism through blood, and therefore, it is necessary to frequently measure a blood pressure to confirm a condition of one's health. Generally, the term `blood pressure` means an arterial blood pressure of the brachial artery. The blood pressure depends upon interrelations between a number of factors, the important ones being: the force of contraction of the left ventricle of the heart as it pumps forth blood; the volume of blood forced into the aorta by the contraction of the left ventricle; the peripheral resistance of the arteries, their elasticity and tone; and the viscosity of the blood. Blood pressure measurement is a standard part of any medical examination. The basic process involves two components: one is the measurement of the pressure of a cuff encircling the arm; the other is the estimation of the blood pressure based on the detection of sounds or oscillations as the cuff is gradually deflated. The sphygmomanometer comprises a cuff which is wrapped around the upper arm. The cuff is inflated by a pump which provides sufficient pressure to compress the brachial artery in the upper arm. A pulsation transmitted from the artery to the cuff is processed by an electrical circuit to determine the blood pressure of a patient. One of sphygmomanometers which have long been well-known is a mercury type sphygmomanometer. By such a mercury sphygmomanometer, pressure is applied to a cuff so as to pressurize a blood vessel. In a following decompression process in which air is discharged from the cuff to release the pressure therefrom, drop of mercury is watched, the systolic pressure or maximum blood pressure is determined by detection of K (Korotkoff) sounds with a stethoscope by a physician and the diastolic pressure or the minimum blood pressure is determined by ceasing of the K-sounds. In an electronic sphygmomanometer an air bag is inflated with air supplied from an air pump to occlude the brachial artery and the air is deflated from the air bag to the outside to depressurize the air bag, and times when the Korotkov sounds are generated and vanished and blood pressures at that times are measured to render numerical expressions, thereby enabling blood pressure measurement to be conveniently carried out. An increasing number of electronic devices is available in which the cuff pressure is detected by an electronic transducer and the blood pressure is derived, either from the oscillations of pressure within the cuff (the oscillometric method) or from electronic detection of the Korotkoff sounds (the auscultatory method).
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