The sphygmomanometer used in the auscultation method to measure blood pressure is composed of a balloon, a cuff and a pressure gauge. The two rubber bladder tubes of the cuff are respectively connected with the balloon and the pressure gauge, and the three form a closed pipeline system. There are two types of pressure gauges: mercury column type and spring type. When measuring blood pressure, first use a balloon to inflate and pressurize the cuff wrapped around the upper arm, and the pressure acts on the brachial artery through the soft tissue. When the applied pressure is higher than the systolic pressure, the balloon is slowly deflated outwards, and the pressure in the cuff drops accordingly. When the pressure in the cuff is equal to or slightly lower than the systolic pressure, the ejaculation follows the contraction. With blood, the blood can rush through the blocked blood vessel to form a vortex, and the sound of pulsation can be heard with the stethoscope. At this time, the pressure value indicated by the pressure gauge is equivalent to the systolic blood pressure.
Continue to deflate slowly to gradually reduce the pressure in the cuff. When the pressure in the cuff is lower than the systolic pressure but higher than the diastolic pressure, a sound can be heard every time the heart contracts. When the cuff pressure drops to equal to or slightly lower than the diastolic pressure, the blood flow is unblocked again, and the sound accompanied by the heartbeat suddenly weakens or disappears. At this time, the pressure value indicated by the pressure gauge is equivalent to the diastolic pressure.
