Endothelial and microvascular function are important elements of overall cardiovascular health. Dysfunction in either or both is predictive of future cardiovascular events, thus preventing or minimizing the degree of dysfunction is critical to constraining the risk of such events. Reactive hyperemia is a transient increase in blood flow that occurs following a period of ischemia (e.g. arterial occlusion) and is indicative of microvascular health. Regular physical exercise is critical as a preventive measure in maintaining the capacity for reactive hyperemia; however, consistent dedication to regular exercise regimens is difficult or impossible for some people. Recent evidence suggests that chronic passive heat therapy (CHT) may result in improvements to cardiovascular health similar to that of exercise. PURPOSE: To examine the effects of 8 weeks of CHT on forearm post-occlusive reactive hyperemia. METHODS: Five, young, healthy and able-bodied university students (21 ± 1 years) underwent hot water immersion 4-5 times per week with a goal of maintaining a rectal temperature of 38.5°C for 1 hour per session for 8 weeks (36 sessions total). Before and after the 8 weeks of CHT, brachial artery blood flow was measured via Doppler ultrasonography for 3 minutes following a 5-minute forearm arterial occlusion. Data are presented as mean ± SE vascular conductance (VC, blood flow divided by mean arterial pressure). RESULTS: In preliminary subjects, change in peak VC from baseline, indicative of microvascular structural changes, increased following CHT from 1.77 ± 0.24 to 2.26 ± 0.20 ml/min/mmHg (p = 0.09) and area-under-the-curve of the hyperemic response, indicative of improvements in endothelial function, increased from 59.7 ± 9.0 to 111.9 ± 13.0 sec.ml/min/mmHg (p = 0.11). CONCLUSION: CHT appears to produce structural and functional changes in the microvasculature comparable to that of exercise training, and could potentially serve as an alternative to exercise for improving cardiovascular health.

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