Respiratory-dependent laser-Doppler flux motion in different skin areas and its meaning to autonomic nervous control of the vessels of the skin.

Abstract The aim of this study is to evaluate and quantify the respiratory dependency of cutaneous laser–Doppler flux motion in two variable innervated sites of the upper extremity (the proximal volar forearm and the fingertip) by using a computer-supported system. Various spontaneous (6–17/min) and externally triggered (12 or 6/min) respiratory frequencies were used for comparative frequency analysis of the laser–Doppler flux signal. Further, an index (MI RSF ) was determined as an indicator of the correlation between flux motion and respiration. The MI RSF is defined as the ratio of the power spectrum of the LDF signal at the specific respiratory frequency divided by the time-averaged LDF for that time period. The MI RSF enables a comparison of different intra- and interindividual flux values. A very high correlation was seen between the respiratory frequency and the MI RSF during spontaneous respiration in the skin of the proximal volar forearm; the lower the spontaneous respiratory frequency, the higher the MI RSF . However, this correlation could not be found in the results of the fingertip. The presence of a constant and therefore externally triggered respiratory frequency increased the modulations of the LDF at both measurement locations. While triggered respiration produced a decline in the taLDF of the fingertip, the taLDF of the forearm was unaffected. Considering the different innervation and hydrostatic effects the results lead to the following conclusion: the finger vessels are richly innervated with adrenoceptors which causes α1-mediated vasoconstriction. In contrast to the vessels of the fingers those of the forearm seem to be under andrenergic as well as cholinergic control. Hydrostatic components appear to be more prevalent in the volar forearm site.