Body cooling attenuates the decrease in maximal oxygen uptake associated with cardiovascular drift during heat stress

Area of Science:

• Exercise Physiology
• Environmental Physiology
• Cardiovascular Physiology

Background:

• Cardiovascular drift (CV drift) during prolonged exercise in heat is linked to reduced maximal oxygen uptake (VO(2)(max)).
• The causal relationship between CV drift and decreased VO(2)(max) under heat stress requires further investigation through experimental manipulation.
• Understanding this relationship is crucial for optimizing exercise performance and safety in hot environments.

Purpose of the Study:

• To experimentally determine if cardiovascular drift (CV drift) causally impacts maximal oxygen uptake (VO(2)(max)) during heat stress.
• To investigate the efficacy of body cooling, specifically fan airflow, in mitigating CV drift and its effect on VO(2)(max).
• To establish a causal link between exercise-induced CV drift and subsequent reductions in VO(2)(max) in a hot environment.

Main Methods:

• Ten healthy men underwent a baseline graded exercise test (GXT) in a temperate environment (22°C) to determine VO(2)(max).
• Participants then completed submaximal cycling trials (35°C) at 60% VO(2)(max) for 45 minutes under three conditions: no cooling (NC), fan airflow (FAN) starting at 18 minutes, and a short 15-minute bout (15 max).
• VO(2)(max) was reassessed immediately after each 45-minute (or 15-minute) trial to measure changes in cardiorespiratory function and VO(2)(max) during the period of CV drift.

Main Results:

• In the no cooling (NC) condition, VO(2)(max) decreased by 18%, heart rate (HR) increased by 16%, and stroke volume (SV) fell by 12% from 15 to 45 minutes (P < 0.05).
• With fan airflow (FAN), the decline in VO(2)(max) was significantly attenuated (5.7% decrease), with smaller increases in HR (4%) and less reduction in SV (3%) from 15 to 45 minutes (P < 0.05).
• The 15-minute trial showed minimal changes, indicating that the observed effects in NC and FAN were related to the prolonged exercise duration and subsequent CV drift.

Conclusions:

• The reduction in VO(2)(max) associated with cardiovascular drift during prolonged exercise in the heat is significantly attenuated by body cooling using fan airflow.
• These findings provide strong evidence supporting a causal relationship between the development of cardiovascular drift and the decrease in VO(2)(max) observed during heat stress.
• Implementing cooling strategies like fan airflow can help maintain exercise capacity by mitigating the negative effects of cardiovascular drift in hot conditions.