Spectral Analysis of Arterial Bruits (Phonoangiography): Experimental Validation

Turbulent flow in arteries produces sound recognized at the skin surface as a bruit. Spectral analysis of such bruits (phonoangiography) is the basis for a simple, noninvasive method of quantifying arterial stenosis. In human studies of carotid stenoses, the spectral break frequency of the bruit (f0) (frequency beyond which bruit amplitude drops sharply) was directly related to the angiographic residual lumen diameter (d), i.e.,d = U/fo, where U is flow velocity. In the clinical situation, flow velocity remains relatively constant because of cerebrovascular autoregulation. In order to test the effects of flow velocity on bruit frequency, we have correlated,under controlled conditions, stenosis anatomy, blood flow, and the sounds originating from an abdominal aortic stenosis produced in adult mongrel dogs by external application of a 5-mm wide Teflon band.Aortic flow was measured in arbitrary units with an electromagnetic flowmeter and varied by stepwise constriction of bilateral femoral arteriovenous fistulas. Bruits were recorded on tape and analyzed by computer.The relationship between flow through the stenosis and break frequency of the bruit was linear (r = 0.89) in 10 dogs. Where d was altered in three other dogs, the relationship between flow and break frequency remained linear for each different d.The data suggest that the relationship between break frequency, flow velocity and residual lumen diameter holds over a wide range of values of each of those variables.