Implantable Doppler ultrasonic vessel patency monitor

An implantable, extractable Doppler ultrasonic flow probe has been developed for monitoring the patency of small vessels following surgical anastomosis. Measurement of vessel area and Doppler angle are not required, as the instrument algorithm utilizes Gauss´ law and the Doppler weighted Fourier spectrum to calculate flow. Bench tests show reasonable repeatability (s.d./mean=0.03) and correlation (r=0.951) with timed volume methods. Animal trials in the dog resulted in successful monitoring for up to nine days followed by probe extraction with no vessel damage. A 24% increase in observed flow when vessel cross-sectional area was halved at constant flow suggests a sensitivity to changes in the ultrasonic attenuation