Sounds heard through a stethoscope while the cuff pressure of a sphygmomanometer is gradually lowered. Sounds are first heard at systolic pressure, and they disappear at diastolic pressure.
gauge attached to the cuff, at which sounds are first heard as the cuff pressure is lowered is identified as the systolic blood pressure.
As the pressure in the cuff is lowered farther, the duration of blood flow through the artery in each cycle becomes longer. When the cuff pressure reaches the diastolic blood pressure, all sound stops because flow is now continuous and nonturbulent through the open artery. Thus, diastolic pressure is identified as the cuff pressure at which sounds disappear.
It should be clear from this description that the sounds heard during measurement of blood pressure are not the same as the heart sounds described earlier, which are due to closing of cardiac valves.
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