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| Typical Number in Hospital: 3 | Cost Bands: 4 | References: 1 |
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 commonly identified in the operating theatre, ward, clinic or doctor's surgery using a sphygmomanometer. In this case an inflatable cuff is placed around the upper arm and the pressure in the cuff inflated above the systolic pressure (typically 120 mmHg) and then slowly released as sounds from the artery downstream of the cuff are detected using a stethoscope placed on the lower arm. The systolic pressure is identified as blood first begins to spurt through the artery which has been held closed by the cuff pressure. The diastolic pressure is identified by a different sound when the artery is just failing to close.
The stethoscope can be replaced by a thin ultrasonic transducer placed under the inflatable cuff which detects the movement of the artery wall. The doppler signals are detected and fed to a pattern recognition circuit which identifies the characteristic signals occurring as the cuff pressure falls past the systolic and diastolic pressures.
These devices are claimed to be more accurate than alternative (acoustic) methods when the pulse is weak, or when there is patient movement or high background noise.
The device contains a double piezoelectric transducer (one section for receive, the other for transmit) coupled to the skin with a jelly, an oscillator to energize the transmit transducer, a receiving amplifier, and a doppler detector and pattern recognition circuit. Sometimes the pressures are recorded on a paper chart to monitor the trend.
Content and Design Copyright 2000 Dr. Malcolm C Brown. See Title Page for more details