Determination of the hemodynamic factors which influence the carotid Doppler spectral broadening.

In the diagnosis of extracranial carotid arterial disease, quantitative measurements from the continuous wave (CW) Doppler spectrum have the potential for detecting stenoses and occlusions. The measurement of maximum peak Doppler frequency at the site of stenosis has been shown to detect severe, but not minor or moderate, stenoses. Diagnosis of minor or moderate stenoses may be possible by assessing the degree of flow disturbance beyond the stenosis. Such flow disturbances cause the Doppler spectrum at peak systole to be broadened, and it has been suggested that the measurement of spectral broadening may be of diagnostic value. This paper describes the results of an in vitro study aimed at determining the hemodynamic factors that influence the severity of the Doppler spectral broadening. The spectral broadening index (SBI) at peak systole, defined as SBI = 1 - Fmean/Fmax, was used to quantify the instantaneous spectrum. In a pulsatile flow in vitro model that produced spectral waveforms virtually identical to those recorded in the human carotid, we observed a direct linear relationship between SBI and the severity of stenosis, at least for those stenoses having greater than 40% cross-sectional area (R = 0.82 to 0.93). The SBI was found to be maximum when recorded immediately beyond the stenosis and returned to normal 4-5 cm downstream from the stenosis. The SBI was higher for nonsymmetrically shaped stenoses than for symmetrical stenoses for lesions greater than 60%, but not for stenoses less than 60%. In this model, the SBI recorded from both normal or abnormal waveforms was not affected by the flow rate.(ABSTRACT TRUNCATED AT 250 WORDS)