Human thermoregulation: separating thermal and nonthermal effects on heat loss
Glen P. Kenny1, W. Shane Journeay2
1
Human and Environmental Physiology Research Unit, Laboratory for Human Bioenergetics and Environmental Physiology, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada, K1N 6N5, 2Dalhousie Medical School, Dalhousie University, Faculty of Medicine, Halifax, Nova Scotia, B3H 4H7, Canada
TABLE OF CONTENTS
- 1. Abstract
- 2. Introduction
- 3. Overview of skin blood flow control
- 4. Thermal factors influencing skin blood flow
- 5. Nonthermal factors influencing skin blood flow
- 5.1. Baroreceptors and skin blood flow under thermoneutral conditions
- 5.2. Baroreflex control of skin blood flow during hyperthermia
- 5.3. Central command
- 5.4. Metaboreceptors
- 6. Overview of eccrine sweat gland control
- 7. Thermal factors influencing eccrine sweating
- 8. Nonthermal influences on eccrine sweating
- 8.1. Central command
- 8.2. Metaboreceptors
- 8.3. Baroreceptors
- 8.4. Considerations
- 9. Postexercise thermoregulation - overview
- 10. Nonthermal baroreflex modulation of postexercise heat loss responses
- 11. The relative contribution of nonthermal input on postexercise heat loss responses
- 12. Other factors
- 12.1. Level of hyperthermia
- 12.2. Hydration status
- 12.3. Sex-related differences
- 13. Human heat balance during and following dynamic exercise: A calorimetric perspective
- 14. Time course of thermogenesis and thermolysis during and following steady-state exercise
- 15. Calorimetric evidence for nonthermal modulation of whole-body heat loss
- 16. Summary
- 17. Acknowledgments
- 18. References
1. ABSTRACT
Human thermoregulatory control during heat stress has been studied at rest, during exercise and more recently during exercise recovery. Heat balance in the body is maintained by changes in the rate of heat loss via adjustments in skin blood flow and sweating. Independent of thermal control, the actions of nonthermal factors have important consequences in the control of heat loss responses during and following exercise. While the effect of these nonthermal factors is largely considered to be an inhibitory or excitatory stimulus which displaces the set-point about which temperature is regulated, their effects on human thermoregulatory control are far reaching. Many factors can affect the relative contribution of thermal and nonthermal influences to heat balance including exercise intensity, hemodynamic status, and the level of hyperthermia imposed. This review will characterize the physiological responses associated with heat stress and discuss the thermal and nonthermal influences on sweating and skin blood flow in humans. Further, recent calorimetric evidence for the understanding of thermal and nonthermal contributions to human heat balance will also be discussed.
