Totally implantable directional Doppler flowmeters.

Two totally implantable Doppler blood flowmeters have been developed for the chronic measurement of deep-body flows; made possibly by two custom-integrated circuits. The CW and pulsed Doppler instruments are small (less than 2.5 cm3), use little power (less than 30 mW), and have excellent baseline stability. The pulsed Doppler flowmeter is applied principally when velocity-profile information or a nonencircling transducer assembly is required but where minimal restraint of the animal for inductive telemetry is permissible. Using a circumferential cuff, the CW Doppler flowmeter monitors Doppler data over a at least a 3-meter range by means of RF telemetry and produces a single velocity estimate. These instruments compliment each other and other telemetry systems by proving the researcher with alternatives for the long-term measurement of deep-body flow without percutaneous leads.