By means of determining the dependence of blood flow rate and different indices on the spectral characteristics of the ultrasonic Doppler response of blood flow the issue of improving the measurement efficiency of vascular system diagnostic parameters is studied. It is shown that instantaneous power of the Doppler signal allows to draw the conclusion about varying of blood flow diameter during the cardiocycle. On the basis of the analytical expressions for the instantaneous power of the Doppler signal, which consider the focusing of waves at an arbitrary ratio between duration of the probing pulses and blood vessel diameter, the expressions for Stuart, Gosling and Pourcelot indices as well as blood flow rate are derived. These expressions allow to set the degree of the diagnostic value of the proposed new indices of blood flow and improve the method of determining blood flow rate in ultrasound Doppler systems. References 17, figures 5
