Evaluating microcirculation by pulsatile laser Doppler signal

Abstract

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 & after stimulus. Using the heartbeat as a trigger, we investigated whether the relation between pressure & 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 & flux segment with a synchronized-averaging method: peak delay time (PDT), pressure rise time & flux rise time (FRT). The abdominal aortic blood pressure & renal cortex flux (RCF) signals were measured in spontaneously hypertensive rats (SHR) & Wistar Kyoto rats (WKY). The mean value of the RCF did not differ between SHR & 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.