Meta-analysis of heat-induced changes in cardiac function from over 400 laboratory-based heat exposure studies

Area of Science:

• Environmental Physiology
• Cardiovascular Physiology
• Climate Health

Background:

• Heat waves are linked to increased cardiovascular fatalities.
• Existing research on heat's cardiac effects often uses artificial heating methods like water-perfused suits.
• Understanding cardiac responses to natural heat exposure is crucial for public health.

Purpose of the Study:

• To synthesize existing research on human cardiac responses to heat exposure.
• To compare cardiac responses between encapsulated and natural heat exposure simulations.
• To provide empirical data on physiological responses during heat waves.

Main Methods:

• Meta-analysis of over 400 laboratory-based heat exposure studies (1961-2024).
• Inclusion of 6858 participant-exposures.
• Multilevel mixed-effects modeling to analyze cardiovascular and temperature data.

Main Results:

• Median core temperature and heart rate increased by 0.9°C and 27 bpm, respectively.
• Encapsulated heating modalities led to higher heart rate, cardiac output, and cardiac workload.
• Encapsulated methods also resulted in blunted decreases in systolic blood pressure.

Conclusions:

• Laboratory findings may overestimate cardiac strain due to artificial heating methods.
• Realistic heat exposure research is vital for accurate climate health models.
• Improved understanding is needed for effective heat-health guidance amidst rising global temperatures.