The application of an improved dual-slit photometric analyzer for volumetric flow rate measurements in microvessels

The dual-window photometric analyzer is currently a widely used instrument to estimate volumetric flow rates in microvessels. This instrument provides an analog voltage that is proportional to cell velocity, but the question arises how this voltage is related to the mean velocity in the blood vessel. It requires a separate investigation and in this report a calibration of an improved version of a dual-window photometric analyzer for volumetric flow rate measurements in microvessels as large as 470 microns in diameter is presented. The relationship between correlator velocity and blood mean velocity is presented in a closed empirical form. Within a 5% error of the mean it is found to be dependent on tube diameter but independent of hematocrit (between 3 and 40%). A rotating transparent disc plated with dried red blood cells was used to test the dynamic response of the instrument for frequencies up to 10 Hz. The amplitude reduction was less than 10% up to 3 Hz. Thereafter it fell off at 6 db/octave.