An integral pulse frequency modulated gas microbubble detector is described. When used in conjunction with an electromagnetic blood flowmeter, the ultrasound pulse repetition frequency can be regulated to reduce multiple counting errors due to variations in blood flow rate. A special detector mounting head eliminates problems due to wall curvature and pulsation, permits reliable and reproducible transducer coupling and makes it possible to gate the ultrasound field electronically in order to avoid spurious counts due to crystal and wall artefacts and low intensity regions.
Results obtained from the detector during an in vitro evaluation of bubble oxygenators suggest that the number of arterial line gas microbubbles is less than has been claimed previously and that the total volume of gas liberated in the form of microbubbles may be too small to have any demonstrable primary clinical effects.
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