Heat Hyperemia or Reactive Hyperemia Alone Do Not Elicit Maximum Skin Blood Flow

Abstract

The cutaneous circulation has been proposed as a model of generalized microvascular function which could be monitored noninvasively using laser doppler flowmetry. The response to heat hyperemia is commonly used to monitor disease or treatment related changes in microvascular function under the assumption that this represents maximum blood flow. We hypothesized that heat hyperemia alone does not elicit maximum skin blood flow. Purpose To understand how skin blood flow responds to heat hyperemia (HH), reactive hyperemia (RH), and a combination of both stimuli. Methods Ten healthy adults (30 ± 5 years; 74 ± 16.5 kg, mean ± SD) were subjected to 3 different conditions: reactive hyperemia (skin temp controlled at 33°C), heat hyperemia (skin heated to 42°C for 40 minutes), and HH + RH. Two Peltier-controlled thermomodules with laser doppler flow probes were placed on the right forearm to measure skin blood flow. A rapid release cuff on the right upper arm was inflated to 220 mmHg for 5 min to elicit RH while laser doppler flow (LDF) was monitored continuously from 1 min before cuff inflation (baseline) to 3 min after cuff release. This procedure was performed with skin temperature at 33°C and again after 40 min of local heating to 42°C. The mean of the two LDF probes was used in determining the highest 1-sec average skin blood flow for each condition. Beat-by-beat mean arterial pressure (MAP) was obtained by a photoplethysmographic sensor on the middle finger of the left hand. Cutaneous vascular conductance (CVC) was calculated as LDF / MAP. Results Both HH and RH increased LDF and CVC above baseline values (p<0.001). The highest 1-sec LDF and CVC averages were significantly higher during HH+RH when compared to RH or HH (*p < 0.001). Conclusion These results indicate that maximum blood flow and vasodilation are greater during combined heat and reactive hyperemia than during reactive hyperemia or heat hyperemia alone. Future studies should consider using a combination of HH and RH rather than HH alone to assess maximum cutaneous vasodilation.