A Physiologically-based Framework to Evaluate Possible Risk Factors for Heat-Related Illnesses

A physiologically-based framework is developed to understand key risk factors associated with adverse health effects from heat waves. The framework consists of a physiological model with associated inputs, including environmental conditions and behavioral responses. The physiological model predicts core temperature over time, then converts this trajectory into a time-at-temperature metric. The output of the framework is a heat-related health effects index (HEI). The framework is flexible, allowing the individual sub-models to be revised and updated as new information becomes available. Scenario analyses are easily accommodated, enabling the framework to evaluate issues such as intervention strategies and the possible effects of global climate change on heat-related illnesses. The framework was applied to conditions during the 1995 Chicago event and the results compared with published studies. There was reasonably good agreement between HEI ratios and actual mortality risk ratios when comparing different environmental conditions (indoor vs. outdoor). Predicted HEI ratios were significantly smaller than actual mortality ratios when comparing healthy vs. compromised populations, supporting the notion that mortality may not be the best indicator of heat stress effects.