Description of a pulsatile flow field downstream from an orifice-like stenosis

The mechanisms of generation and propagation of acoustic murmurs in the cardiovascular system are studied in an in-vitro, bench-top model using a confined pulsatile jet. The stenosis geometry suggested by the isthmic form of coarctation of the aorta has been modeled to examine the distal flowfield velocity profiles. Excised coarctation segments and corresponding pre-operative aortograms were carefully examined to develop the flow model. The aortograms recorded under physiological pressures indicated the presence of a small jet that persisted through systole and diastole. Several model stenoses were constructed from clear plastic. Clear water at room temperature was propelled through the models with a pneumatically driven pulsatile pump. Comparisons were also made to steady flow. Quasi-steady state conditions were maintained throughout each of the pulsatile experiment runs. Observations were made for both the systolic and diastolic phases. During systole a jet develops which grows and decays in a manner similar to steady flow predictions. Frequency analysis shows that the Strouhal number predictions for orifice flow are valid for the quasi-steady state systolic flow. This relationship suggests a non-invasive technique which may be used to determine stenosis size and mean velocity.