Detection of subcritical stenoses by Doppler spectrum analysis.

Little information is available regarding the sensitivity of carotid Doppler signal spectral analysis in documenting flow disturbances caused by subcritical stenotic lesions. We have studied the effects on spectra of stenoses ranging from 10% to 80% diameter reduction using the infrarenal aorta of the dog. Spectral analysis was able to reliably detect stenoses as small as 20% by comparison of the peak systolic frequency at the site of stenosis with that proximal to it; a peak frequency ratio of about 1.5 was typical for this degree of stenosis. This ratio continued to increase in the nearly linear fashion with increasing stenosis, reaching approximately 2.1 for a 50% stenosis. For greater degree of stenosis, turbulent flow patterns and significant spectral broadening were noted a gradual decrease in the peak frequency ratio. Spectra of Doppler signals recorded at sites 1 cm or more distal to the stenosis site were not significantly different from proximal spectra until the stenosis exceeded a 45% diameter reduction and the peak frequency ratio 1.3. At these distal sites this ratio increased with increasing stenosis to a maximum of 1.64 for a 65% stenosis, beyond which the flow was characterized by severe turbulence and a decreasing ratio. Doppler signal spectrum analysis appears to be a potentially quantitative noninvasive technique that has the sensitivity necessary to detect subcritical carotid arterial stenoses and be applicable to the clinical setting.