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Cutaneous vascular reflexes during exercise in the heat
A Tripathi1, G W Mack, E R Nadel
1John B. Pierce Laboratory, Yale University School of Medicine, New Haven, CT 06519.
Medicine and Science in Sports and Exercise
|December 1, 1990
Summary
Hypovolemia during exercise in heat reduces forearm venous compliance, but does not affect blood flow or arterial pressure. Central venous pressure changes are linked to forearm venous compliance and stroke volume, suggesting baroreceptor reflexes maintain cardiac output.
Area of Science:
- Environmental Physiology
- Cardiovascular Physiology
Background:
- Thermoregulation during exercise is crucial for maintaining homeostasis.
- Cardiac filling pressure influences cardiovascular responses during physical activity.
Purpose of the Study:
- To investigate the impact of hypovolemia on cutaneous vascular responses during exercise in heat.
- To determine the role of cardiac filling pressure in modulating these responses.
Main Methods:
- Cycle ergometer exercise at 50% VO2max in 35°C heat.
- Comparison between normovolemic and hypovolemic (19.5% plasma volume reduction) conditions.
- Measurement of cardiac output, heart rate, stroke volume, forearm venous compliance, and blood pressure.
Main Results:
- Cardiac output was maintained in both conditions.
- Hypovolemia led to higher heart rate and reduced forearm venous compliance (FVC).
- Forearm blood flow and arterial pressure remained unaffected by hypovolemia.
Conclusions:
- Reduced central venous pressure in hypovolemia correlates with lower FVC and stroke volume.
- Peripheral vascular reflexes, possibly mediated by low-pressure baroreceptors, help maintain cardiac output during exercise in heat.