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Sustained and generalized extracellular fluid expansion following heat acclimation
Mark J Patterson1, Jodie M Stocks, Nigel A S Taylor
1Department of Biological Science, University of Wollongong, NSW, Australia. mark.patterson@dsto.defence.gov.au
The Journal of Physiology
|June 26, 2004
Summary
Heat acclimation significantly expands plasma volume (PV) and extracellular fluid (ECF) in males. This fluid expansion is sustained throughout prolonged exercise-heat acclimation, indicating a non-selective increase in the extracellular compartment.
Area of Science:
- Exercise Physiology
- Environmental Physiology
- Body Fluid Regulation
Background:
- Heat acclimation protocols are used to improve physiological responses to exercise in hot environments.
- Understanding changes in body fluid compartments during heat acclimation is crucial for performance and health.
- Previous research has investigated plasma volume (PV) expansion, but its sustained nature and selectivity during prolonged acclimation require further investigation.
Purpose of the Study:
- To investigate the changes in intra- and extravascular body-fluid compartments during a 3-week exercise-heat acclimation protocol.
- To determine if the acclimation-induced plasma volume expansion is selective or a general expansion of extracellular fluid.
- To assess if the plasma volume expansion can be sustained during prolonged heat acclimation.
Main Methods:
- 12 healthy males underwent a 3-week exercise-heat acclimation protocol involving cycling in a hot environment (39.8°C, 59.2% RH).
- Body fluid compartments, including plasma volume (PV) and extracellular fluid (ECF), were measured on day 1 (control), day 8, and day 22.
- Measurements included plasma electrolyte, total protein, and albumin concentrations to assess fluid shifts and composition.
Main Results:
- Plasma volume (PV) was significantly expanded and maintained on day 8 (48.8 ml kg⁻¹) and day 22 (48.8 ml kg⁻¹) compared to control (44.0 ml kg⁻¹).
- Extracellular fluid (ECF) was also significantly expanded on day 8 (318.6 ml kg⁻¹) and day 22 (308.4 ml kg⁻¹) compared to control (279.6 ml kg⁻¹).
- Plasma electrolyte, total protein, and albumin concentrations remained unchanged, but their total plasma content increased, indicating fluid dilution.
Conclusions:
- The acclimation-induced plasma volume expansion is sustained throughout prolonged exercise-heat acclimation.
- The expansion of plasma volume is not selective but represents a ubiquitous expansion of the extracellular fluid compartment.
- These findings highlight the body's adaptive capacity to maintain fluid balance during sustained heat exposure through exercise.