The study of microvascular function can be routinely performed in humans using laser Doppler flowmetry (LDF) of the skin. Post-occlusive reactive hyperemia (PORH) and local thermal hyperemia (LTH) are used as tools to investigate endothelial and neurovascular microvascular functions. Sodium nitroprusside (SNP) iontophoresis is a commonly used technique to assess non endothelium-dependent skin microvascular function. However, there is no consensus over their reproducibility and variation over time, with room temperature, prandial status, and stress. Our objective was to test the reproducibility of those techniques on the finger and on the forearm, and their physiological variations.
We performed local heating up to 44°C, 5min postocclusive hyperemia and SNP iontophoresis in fourteen healthy volunteers, at day 0, day 7 and month 6. We also tested the impact of a standard meal, of variations of room temperature, and of a psychological stress (Stroop test). Cutaneous blood flow was recorded with LDF probes. Data are expressed as cutaneous vascular conductance (CVC) in mV/mmHg, as % of maximal vasodilation and as a function of baseline. Reproducibility data are expressed as intra-subject coefficient of variation (CV) and intraclass correlation coefficients (ICC).
One-week reproducibility of PORH and LTH on the finger pad is very good when expressed as CVC raw values (CV=12.6 to 23.7 %, ICC>0.71). On the dorsum of the finger and the forearm, reproducibility was better when expressed as a % of maximal vasodilation (CV=11.9 to 26.4 %, ICC>0.55). SNP iontophoresis did not lead to a vasodilation on the finger pad. On the dorsum and the forearm, its reproducibility was poor. Room temperature had a significant influence LTH and PORH hyperemia parameters, especially on the finger pad.
Reproducibility was very good for both PORH and LTH, but the way of expressing data plays a key role. Reproducibility of SNP iontophoresis was poor. Room temperature (especially when elevated) influenced both PORH and LTH responses on the finger pad, highlighting the need for temperature-controlled conditions while performing these tests.
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