Photoelectric measurement of blood flow during hemodialysis

Accurate measurements of blood flow rate during hemodialysis are essential for determinations of hemodialyzer performance. Despite the availability of a variety of electronic blood flow meters, use of such instruments for determination of blood flow in hemodialysis has never been satisfactory, a situation caused by such factors as the need to recalibrate frequently, the necessity of incorporating transducers into the dialyzer blood circuit and the effect which variables such as hematocrit may have on the accuracy of determination. Furthermore, such devices are expensive and often require the periodic services of an electronics specialist to maintain them in an operable condition.An alternative technique for measuring flow rate in the extracorporeal blood tubing consists of timing the passage of an injected air bubble between two points in the tubing. Since the advent of maintenance dialysis, the “racetrack and bubble time” technique [1] has been widely used for routine determinations of blood flow rate. Data derived from research studies in which this method of flow determination was employed have been published widely, in spite of the relative inaccuracies of the method