A very concise description of automated blood pressure measurement.
When new medical doctors are taught to take blood pressure, they are taught to listen to the sounds through their stethoscope while inflating and then slowly deflating the arm cuff. This instrument is called the sphygmomanometer. There are distinct sounds that one hears as the artery is occluded by the cuff and then slowly opens when the cuff pressure is increased. Listen to the video below to listen to the sound. These sounds are in 5 phases and are called Korotkoff sounds. They represent blood pulsing past the occluded artery as the artery is opened. This method of blood pressure measurement was colled
Automatic instrumentation to measure blood pressure was being developed and in the earlier generation of machines, they used an audio microphone to measure the sounds. This sometimes led to issues since if the microphone was not in the correct place then the sound could be missed and leading to failed measurements.
New instrumentation was then invented that could still measure the occlusion of the artery. But this time it used a very sensitive pressure detector that detected the oscillation of the artery, rather than the sound, to determine when the artery was blocked and then released. It turns out that from the time of occluding the artery to its opening the artery vibrates. This vibration decreases and then increases and can be measured accurately. This is the principle that is used in most automatic blood pressure measurement machines.
{youtube}VdpsyZnFLNU{/youtube}