ULTRASONIC BLOOD PRESSURE MONITOR

Arterial blood pressure has a peak (systolic) pressure occurring when the heart pumps, and a trough (diastolic) just before the next pumping stroke. These two pressures are important indicators of the state of the patient in a number of situations and they are commonly measured by doctors using a mercury-type manometer, an inflatable cuff round the upper arm, and an inflation and deflation device. The cuff pressure corresponds to the systolic pressure when the artery in the arm (brachial artery) just fails to open, and this condition can be detected using a stethoscope on the arm downstream from the cuff. The diastolic pressure is identified as that point when the artery just fails to close. The characteristic sounds (Korotkoff sounds) for these two conditions are recognized by the experienced ear. However, accurate identification is difficult in case of weak pulse, high background noise, or patient movement.

An ultrasonic blood pressure monitor uses the same inflation and deflation sequence to scan the two pressures but the opening of the artery is detected using an ultrasonic doppler device which responds to the movement of the artery wall. A thin ultrasonic transducer is placed on the skin under the inflatable cuff, and coupled to the skin with a jelly to avoid an air gap.

Such devices may be found in operating theatres, wards and some clinics. They may have an automated inflation-deflation sequence to permit repeated measurement and/or recording during anaesthesia or intensive care. The main advantage claimed over acoustic techniques is the high noise immunity and movement noise rejection.

Components of the device are an ultrasonic transducer, an oscillator (e.g. 2 MHz), a high-frequency amplifier, doppler detector and a pattern recognition circuit. Sometimes the pressures are recorded on a paper chart. An example of an ultrasonic blood pressure monitor is the Arteriosonde.

Content and Design Copyright 2000 Dr. Malcolm C Brown.  See Title Page for more details