EVALUATION OF 2 SYMPATHETIC CUTANEOUS VASOMOTOR REFLEXES USING LASER-DOPPLER FLUXMETRY

Disturbances in sympathetic cutaneous vasomotor reflexes may be of pat hogenetic importance in several microvascular problems. Laser Doppler fluxmetry (LDF) enables one to study the influence of sympathetic refl exes on skin blood flow. A matter of concern is the high variability o f skin blood flow and its reactivity to sympathetic reflex test result ing in a poor reproducibility. In this study we evaluated two sympathe tic stimulation tests, distant cooling and inspiratory gasp, and their influence on LDF-measured skin blood flow of the pulp of the big toe in 63 healthy volunteers. No age or sex dependency of the LDF test res ults was found. Absolute and relative LDF decrease during distant cool ing was highly variable between the subjects (LDF decrease, mean +/- S D: 0.7 +/- 5.3%) compared to an LDF decrease of 46.5 +/- 3.1% during a n inspiratory gasp test. The reproducibility, however, was better for the distant cooling test [coefficient of variation (CV): distant cooli ng: 5.8%, inspiratory gasp test: 35.4%]. With the use of a thermostati cally controlled LDF probe holder fixed at a temperature of 36 degrees C, the short-term reproducibility of the two sympathetic vasomotor te sts did not improve, probably because of a steady increase in baseline skin blood flow during the test. Surprisingly long-term variability o f the percentage LDF decrease during the inspiratory gasp test, perfor med with the heated LDF probe, was lower compared to the short-term va riability (CV 19.2 vs. 39.0%, p < 0.05). In conclusion to study sympat hetic skin vasomotor reflexes with LDF, vasoconstriction during the in spiratory gasp test was more uniform compared to the distant cooling t est, although the latter was more reproducible. Measuring skin blood f low reactivity with a heated LDF probe (36 degrees C) did not improve reproducibility.