Reproducibility of four frequently used local heating protocols to assess cutaneous microvascular function.

BACKGROUND: Skin microvascular responses to local heating are frequently used to assess microvascular function. Several local heating protocols have been developed, all varying slightly in execution. The aim of this study was to determine the inter-day reproducibility of the four most commonly used local heating protocols in healthy young subjects. METHODS: Fifteen, healthy males (28+/-5yrs, BMI 25+/-2kg/m2) attended two experimental trials 2-7days apart. During each trial, baseline and maximal thermally stimulated forearm skin responses were examined simultaneously at four sites on the dominant forearm using laser Doppler flowmetry (LDF). The following heating protocols were adopted: 1. Rapid 39 degrees C (0.5 degrees C/5s), 2. Rapid 42 degrees C (0.5 degrees C/5s) 3. Gradual 42 degrees C (0.5 degrees C/2min 30s) and 4. Slow 42 degrees C (0.5 degrees C/5min). The coefficient of variation (CV) was calculated for absolute flux, cutaneous vascular conductance (CVC; flux/mean arterial pressure, MAP) and CVC expressed as a percentage of maximal CVC at 44 degrees C (%CVCmax) at three different time points; baseline (33 degrees C), plateau (39/42 degrees C) and maximal (44 degrees C). RESULTS: Reproducibility of baseline flux, CVC and %CVCmax was 17-29% across all protocols. During the plateau, Rapid, Gradual and Slow 42 degrees C demonstrated a reproducibility of 13-18% for flux and CVC and 5-11% for %CVCmax. However, Rapid 39 degrees C demonstrated a lower reproducibility for flux, CVC and %CVCmax (all 21%). Reproducibility at 44 degrees C was 12-15% for flux and CVC across all protocols. CONCLUSION: This is the first study examining inter-day reproducibility across four local heating protocols. The good-to-moderate reproducibility of the Rapid, Gradual and Slow 42 degrees C protocols support their (simultaneous) use to assess microvascular function. Using Rapid 39 degrees C may require a greater number of subjects to detect differences within subjects