Key result
An ultrasonic interferometric technique using an asymmetrical extravascular probe successfully measured blood flow velocity in long-term telemetry implants for over three months.
An ultrasonic interferometric technique using an extravascular probe provides stable and sensitive blood flow measurements suitable for long-term telemetry implants.
Supports feasibility of chronic extravascular ultrasonic flow telemetry in models; leaves open clinical translation and safety validation.
An ultrasonic interferometric technique of measuring blood flow with an extravascular probe is presented and analyzed. The difference in phase between pulses of ultrasonic energy transmitted simultaneously from a pair of barium titanate crystals diagonally through the vessel and received by the same pair of crystals is employed as the basic measurement of blood flow velocity. It is shown that the sensitivity is influenced mainly by variability in the internal diameter of the vessel and the zero-flow baseline voltage position is influenced principally by variations in the level of energy reflected from the vessel surfaces. Baseline stability is enhanced by the use of an asymmetrical probe which minimizes the variable reflection components. This measurement technique is currently being employed in long term telemetry implants in which flow measurements have been satisfactorily performed for periods in excess of three months duration.
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Rader et al. (1974) studied this question. Ultrasonic interferometric technique with an extravascular probe was evaluated on Blood flow velocity measurement. An ultrasonic interferometric technique using an asymmetrical extravascular probe successfully measured blood flow velocity in long-term telemetry implants for over three months.
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