Performance of a cuff-type blood flowmeter in vivo.

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Abstract
A T cannula is inserted into the artery within the carotid loop in the neck of a sheep. A cuff-type electromagnetic probe is implanted on the same artery caudal to the loop. While occluding the artery cranial to the cannula, a measured volume of blood can be passed through the probe via the side arm. Thus repeated calibration in the conscious sheep is possible with accurate flow 0. Five implants gave useful observation over 9-19 days. The sensitivity in vivo was 67-93% of that in vitro in accord with existing theory. Systematic trends in sensitivity during implantation were not associated with changes in electrode impedance. Postmortem observations of sensitivity indicated a need for caution in the application of such data to the living animal. Stable blood flows between 130 and 420 ml/min. were superimposed on 0 errors from -100 to +370 ml/min. The breakdown of insulation between magnet coils and electrodes is discussed as a possible source of 0 error.