Effects of stenosis on transit-time ultrasound measurements of blood flow

Measurement of blood flow with transit-time ultrasound near atherosclerotic stenosis sometimes yields anomalous results. The flow-versus-time waveform develops a chaotic pattern obscuring its pulsatile character, and the measured average flow may be less than the real flow thought present. Believing that disturbed flow secondary to atherosclerotic stenosis interferes with transit-time measurements, we investigated the effects of stenosis in a bench model of arterial flow. The average flow measurements and flow-versus-time waveforms produced by the transit-time flowmeter were studied in relation to: (1) the position of the transit-time probe proximal or distal to a stenosis; (2) the choice of filters employed to process the analog output from the flowmeter; and (3) the severity of the stenosis. The results confirm that high grade (> 50%) stenosis creates a characteristic chaotic artifact in the transit-time waveform and, when severe, causes an underestimation of flow.