Key result
The ultrasonic flowmeter overestimates net fluid velocity by 33% in steady laminar flow and 7% in steady turbulent flow, but detects aortic flow waveforms with satisfactory fidelity.
The ultrasonic flowmeter overestimates fluid velocity depending on the flow profile, but detects aortic flow waveforms with satisfactory fidelity for most applications.
Requires flow-specific corrections for velocity accuracy; leaves open waveform use in aortic monitoring pending validation.
The principle of operation of the ultrasonic flowmeter, detecting phase shifts or pulse transit times, is examined. It is shown both theoretically and experimentally that the sensitivity of the flowmeter depends on the fluid velocities averaged along the path of the ultrasound between the transducers. The instrument therefore overestimates the net fluid velocity by 33 percent in case of steady laminar flow and by approximately 7 percent in case of steady turbulent flow, provided the ultrasound traverses the entire lumen of the (cylindrical) vessel. The signal obtained in case of oscillatory flow generally is larger in amplitude than and lagging in phase behind the true flow. The errors are between 0 and 33 percent and between 0 and 7°, respectively. The effect of this on natural blood flow signals is discussed in detail. It is concluded that the flowmeter detects the waveform of aortic flows with a fidelity which should be satisfactory in most cases.
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Urs Gessner (1969) studied Blood flow measurement. Ultrasonic flowmeter vs. True flow was evaluated on Net fluid velocity measurement accuracy. The ultrasonic flowmeter overestimates net fluid velocity by 33% in steady laminar flow and 7% in steady turbulent flow, but detects aortic flow waveforms with satisfactory fidelity.
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