Validation of spectral analytic techniques in the clinical assessment and quantitation of vascular stenoses has been aided by use of in vitro flow loops. We have used a recently developed microprocessor-controlled pulsatile flow model to examine the influence of varying stenoses on Doppler-shifted peak systolic frequencies. A nonaxisymmetric, vertically oriented stenosis was produced by extrinsic compression of latex rubber tubing 12 mm in diameter, reducing the cross-sectional area (CSA) by 25, 40, 50, 60, 70, 85, and 97%. A rolling diaphragm pump, driven through a slider-crank mechanism by a microprocessor-controlled stepper motor, generated characteristic arterial pulse waves at a rate of 75 cycles per minute. Using an 8 MHz, continuous-wave, directional Doppler velocimeter, the Doppler-shifted frequencies were recorded at the stenosis. Four sets of observations were made at each of the stenoses, and the peak systolic frequency (PSF) was determined using a spectrum analyzer. The PSF in the absence of an obstructing stenosis was 2.56 ± 0.03 (KHz ± SEM). This increased significantly (P < 0.05) to 4.80 ± 0.09 when the CSA was reduced by 50%, to 5.90 ± 0.37 when the CSA was reduced by 60% (P < 0.05), to 8.40 ± 0.10 when the CSA was reduced by 70% (P < 0.05), and to 17.84 ± 0.89 when the CSA was reduced by 85% (P < 0.05). These data establish the utility of this pulsatile flow model, confirming the direct relationship between the Doppler-shifted PSF and the percentage reduction in CSA. We recommend use of this or similar models to study those variables influencing the frequency distribution, or flow velocity, across and distal to arterial stenoses.
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