![]() This is detected by the machine which continues to inflate the cuff for a second or two more to ensure that the limb flow has stopped completely. When the cuff encircling a limb is inflated with an electronic pump (or sometimes manually), the rising pressure in the cuff eventually stops arterial blood flowing into the underlying limb and pulsation ceases. With every arterial pulse wave there is a small rise and fall in the volume of the limb, which in turn causes an increase and then a decrease in the pressure within the encircling cuff, which can be detected using a solid-state transducer. Knowing how cuff-only oscillometric readings are estimated helps in understanding the limitations of this method. Listening to these sounds and interpreting them requires training and can be difficult especially if hearing is impaired or there is significant environmental noise. The initial sound approximates to the peak (systolic) and the final sound to the relaxation (diastolic) pressure in the artery. These sounds vary in intensity and usually stop at the point of the lowest pressure within the arteries before the next pulse arrives. As the cuff pressure is deflated the pressure transmitted from the cuff to the walls of the underlying arteries reduces to the point at which blood flow resumes and sounds begin to be heard. The cuff is inflated to a point where the pressure it exerts on the underlying arm is high enough to stop blood flowing underneath so that no blood flow sounds can be heard. The time-honoured, traditional measurement of BP uses an inflatable cuff encircling a limb combined with a stethoscope to detect sounds made by the flow of blood as it comes under the cuff (the Riva-Rocci-Korotkoff auscultatory method).
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