What is the clinical evidence from this study?

Study design: Other. Population: Healthy (n=14). Intervention: Whole body heat stress vs. Normothermic conditions. Primary outcome: Mean arterial pressure (MAP) response (change in mmHg) during postexercise circulatory occlusion (PECO) (p=<0.001).

October 7, 2016Open Access

Whole body heat stress attenuates the pressure response to muscle metaboreceptor stimulation in humans

Q: What are the key findings of this study?

Whole body heat stress significantly lowered the mean arterial pressure response to muscle metaboreceptor stimulation during postexercise circulatory occlusion (change of 12 vs 20 mmHg, P < 0.001).

Key Result

Whole body heat stress significantly lowered the mean arterial pressure response to muscle metaboreceptor stimulation during postexercise circulatory occlusion (change of 12 vs 20 mmHg, P < 0.001).

Structured PICO

Does whole body heat stress alter sympathetic and cardiovascular responses to muscle metaboreceptor and mechanoreceptor stimulation in young healthy subjects?

Population

14 young, healthy, nonhypertensive adults underwent fatiguing isometric handgrip exercise and postexercise circulatory occlusion under normothermic and whole body heat stress conditions.

Intervention

Whole body heat stress (increase internal temperature ~0.6°C via a heating suit)

Comparator

Normothermic conditions

Outcome

Muscle sympathetic nerve activity (MSNA), blood pressure, and heart ratesurrogate

Whole body heat stress attenuates the pressor response to metaboreceptor stimulation and the sympathetic nerve response to mechanoreceptor stimulation in healthy humans.

Main Result

Absolute Event Rate: 12% vs 20%

p-value: p=<0.001

Limitations

Heat stress induced with a heating suit might result in different skin temperature and blood flow distribution than typical exercise.
All heat stress trials were performed after the normothermic trial, so an order effect cannot be completely excluded.
Small sample size.

Abstract

The effects of whole body heat stress on sympathetic and cardiovascular responses to stimulation of muscle metaboreceptors and mechanoreceptors remains unclear. We examined the muscle sympathetic nerve activity (MSNA), blood pressure, and heart rate in 14 young healthy subjects during fatiguing isometric handgrip exercise, postexercise circulatory occlusion (PECO), and passive muscle stretch during PECO. The protocol was performed under normothermic and whole body heat stress (increase internal temperature ~0.6°C via a heating suit) conditions. Heat stress increased the resting MSNA and heart rate. Heat stress did not alter the mean blood pressure (MAP), heart rate, and MSNA responses (i.e., changes) to fatiguing exercise. During PECO, whole body heat stress accentuated the heart rate response change (Δ) of 5.8 ± 1.5 to Δ10.0 ± 2.1 beats/min, P = 0.03, did not alter the MSNA response (Δ16.4 ± 2.8 to Δ17.3 ± 3.8 bursts/min, P = 0.74), and lowered the MAP response (Δ20 ± 2 to Δ12 ± 1 mmHg, P 0.05). These data suggest that whole body heat stress attenuates the pressor response due to metaboreceptor stimulation, and the sympathetic nerve response due to mechanoreceptor stimulation.

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