Abstract: A pair of doppler type ultrasonic transmitters and receiving devices are employed, one operating at a frequency lower than the other. Each of the devices are connected to a demodulator to produce first and second doppler frequency signals, one indicative of vascular blood flow, the other indicative of movement of the vascular wall. The doppler frequencies are fed to a signal processing circuit and a reference stage received as its input, the output of the signal processors. The reference stage produces an output signal on coincidence of the two input signals which is indicative of the heart-beat frequency.

Abstract: In order to perform a non-invasive measurement of the blood flow rate in the smallest vessels, i.e. the capillaries, of a blood vessel bed, and to detect the presence of erythrocyte aggregations therein, acoustic pulses containing oscillations at a frequency above 20 MHz are directed through the skin of a subject from a crystal transducer and the resulting echo pulses are processed to produce information based on the Doppler frequency signals relating to blood flow in a predetermined direction and occurring within a time window corresponding to the distance from the crystal of the blood vessels to be examined. Interspersed between the above-mentioned pulses, spike pulses having a duration of the order of 20 ns are similarly transmitted, and echoes thereof are detected for the purpose of detecting the presence of erythrocyte aggregations.