Effects of surrounding tissue on the sound spectrum of arterial bruits in vivo.

Turbulent flow distal to arterial stenoses producers bruits with a characteristic sound spectrum, analysis of which has permitted accurate non-invasive assessment of the residual lumen diameter of the stenosis in the case of the human carotid artery. In contrast, investigators working with in vitro elastic models of arteries or with excised vessels have reported finding mainly resonant spectra of bruits recorded distal to stenoses. We have studied the effects of turbulent flow on the sound spectrum produced at the arterial wall and the influence of surrounding tissue on this spectrum. Aortic, carotid, and femoral stenoses were produced in dogs by external banding of the arteries with 5mm wide Teflon bands. Recordings of bruits made directly on the vessel wall had a sound spectrum made up of 2 components, one due to turbulent flow, and the second to a superimposed resonant spectrum from arterial wall vibration. This was true of 3 kinds of vessels studied. The effects of surrounding tissue on the sound spectrum of arterial bruits was shown by comparing the spectra o bruits recorded directly on the vessel wall, on the freshly closed wound and on the healed wound. The sound properties of the artery in situ are very different from those of exposed or excised vessels or elastic tubes. Although intravascular turbulence may be accurately appreciated at the skin surface, arterial wall resonance in the intact animal is extensively damped by the normal coupling of the artery to its surrounding tissue.