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Thursday, 11 October 2018

Ultrasonic Blood Pressure Measurement

Ultrasonic Blood Pressure Measurement:

Ultrasonic techniques can he used to measure arterial blood pressure indirectly with the same method as used for flow detection. Here piezoelectric crystals are placed between the patients arm and a blood pressure cuff. The ultrasonic generator generates pulses and these are made to fall on the bronchial artery. Due to the effect of pulses, the blood flow varies. This causes Doppler shift. The Doppler shift is measured by the ultrasonic circuits.

To measure Blood pressure, first the bronchial artery is occluded and since there is no relative velocity between the transmitter and the receiver this time, the Doppler shift is zero. But as the Blood pressure rises so that the arterial pressure is able to overcome the occlusion, a frequency shift is produced (200-500Hz range). This is proportional to systolic pressure. Then as the arterial pressure reaches the diastolic pressure, the frequency shift due to Doppler effect is around 25-100 Hz. So by comparing the frequency shift caused due to each heart beat the blood pressure can be measured by comparing the frequency shifts obtained each time with the standard reference values.

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