Cyclic variation of Doppler power as a function of hematocrit and vessel wall compliance

In order to better understand the relationship between the power of the Doppler spectrum and blood flow abnormalities, a systematic study of all factors that may affect the Doppler power is required. In the study, three important factors were investigated in vitro using a mock flow loop: a) the pulsation rate of the flow, b) the hematocrit of blood and c) the vessel wall compliance. The results may be useful for the development of a noninvasive method for assessing blood vessel wall compliance and fetal hematocrit in utero. The results show that the peak Doppler power decreases 1.5 to 2 dB as the pulsation rate increases from 20 to 55 beats/min. The cyclic variation of the Doppler power is between 2.3 and 6.7 dB at 20 beats/min, depending on the hematocrit, but it drops to 1.6-2.4 dB at 55 beats/min. Moreover, both the time delays of the cyclic variation from the peak systole and the amplitude of the peak of the power are observed to be a function of the hematocrit. This is more evident in compliant vessels at the low beat rate of 20 beats/min. When the vessel becomes more compliant, the Doppler power peak is shifted from the early to the late systole. These results suggested that simultaneous measurements of the time shift of the Doppler power peak relative to the velocity waveform and the magnitude of Doppler power cyclic variation may yield indication as to the value of the hematocrit and vessel compliance