Spectral analysis of the laser Doppler perfusion signal in human skin before and after exercise

Spectral analysis based on wavelet transformation of the periodic oscillations of the cutaneous laser Doppler flowmetry (LDF) signal was used to analyze exercise-induced changes in flow motion in humans. The measurements were performed on the forearm skin in nine healthy, less-trained subjects before and after exercise. Periodic oscillations with frequencies of around 1, 0.3, 0.1, and 0.04 Hz were demonstrated, which are proposed to represent the influence of heart beat, respiration, intrinsic myogenic activity, and the neurogenic factors, respectively, on cutaneous blood flow. We also demonstrated oscillations with a frequency of around 0.01 Hz both before and after exercise. The mean spectral amplitude in the frequency range from 0.0095 to 2.3 Hz increased twofold (P = 0.004) in response to exercise. This increase results from a significant increase in the amplitude of oscillations of around 1, 0.3, and 0.1 Hz. The amplitude of oscillations of around 1 and 0.3 Hz increased onefold in response to exercise (P = 0.02 for both frequencies), whereas the amplitude of oscillations of around 0.1 Hz increased threefold (P = 0.008). Furthermore, to evaluate relative changes of each particular oscillation in response to exercise, the absolute amplitude of each frequency interval was divided by the mean spectral amplitude. In this way, the relative contribution of oscillations of around 0.01 and 0.04 Hz were shown to decrease significantly following exercise (P = 0.008 and P = 0.004, respectively). The relative contribution of the oscillations of around 0.1 Hz increased, although not statistically significant (P = 0.08), while the relative contribution of the oscillations of around 0.3 and 1 Hz to the total flow motion remained unchanged in response to exercise (P = 0.84 and P = 0.95, respectively). These findings indicate an increased contribution of the oscillations of around 0.1 Hz to the regulation of the cutaneous blood flow following exercise, whereas oscillations of around 0.04 and 0.01 Hz contribute less. We conclude that spectral analysis using a wavelet transformation of the LDF signal is a valuable tool for use in the evaluation of exercise-induced changes in the dynamics of cutaneous microvascular blood flow, but further studies are necessary to clarify the physiological origin of these oscillations.