Use of a Local Indicator Dilution Technique for the Measurement of Oscillatory Flow

An indicator dilution method for measuring oscillatory flow in a vessel is analyzed in terms of a mixing chamber with a constant volume. For the correct measurement of mean flow, the time constant of detection of the indicator should be very much shorter than the shortest time constant of the mixing volume. The performance of such a system was examined with a thermal indicator. Although the apparent mixing volume was found not to be constant but to vary with flow, the method showed no significant error in the measurement of mean flow. There was no significant “distance distortion error” when the indicator was detected at two different points downstream from the site of infusion; this was attributed to the pattern of mixing, with detection within or close to the limits of the mixing volume. It is concluded that a properly designed indicator dilution system can measure mean blood flow without significant error, even when there is an socillatory component.