Evaluating microcirculation by pulsatile laser Doppler signal

Laser Doppler flowmetry (LDF) is a popular method for monitoring the microcirculation, but it does not provide absolute measurements. Instead, the mean flux response or energy distribution in the frequency domain is generally compared before and after stimulus. Using the heartbeat as a trigger, we investigated whether the relation between pressure and flux can be used to discriminate different microcirculatory conditions. We propose the following three pulsatile indices for evaluating the microcirculation condition from the normalized pressure and flux segment with a synchronized-averaging method: peak delay time (PDT), pressure rise time and flux rise time (FRT). The abdominal aortic blood pressure and renal cortex flux (RCF) signals were measured in spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY). The mean value of the RCF did not differ between SHR and WKY. However, the PDT was longer in SHR (87.14 +/- 5.54 ms, mean +/- SD) than in WKY (76.92 +/- 2.62 ms; p < 0.001). The FRT was also longer in SHR (66.56 +/- 1.98 ms) than in WKY (58.02 +/- 1.77 ms; p < 0.001). We propose that a new dimension for comparing the LDF signals, which the results from the present study show, can be used to discriminate RCF signals that cannot be discriminated using traditional methods.