An Empirical Mechanistic Framework for Heat Related Illness

A physiologically based, mechanistic framework was developed to understand key risk factors associated with adverse health effects from heat waves. The framework consists of a number of integrated transdisciplinary modules. Environmental conditions and behavioral responses link to a physiological model, which predicts core temperature. Core temperature over time is then converted into a time-at-temperature metric. The output of the framework is a heat-related health effects index (HEI) which reflects the potential relative severity of the heat stress on health. The framework is flexible, allowing the individual models to be adapted to conditions at specific locations and to be 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 and an initial set of component models were applied to conditions during the 1995 Chicago event and the results compared with published studies. For individuals, there was reasonably good agreement between HEI ratios and actual mortality risk ratios when comparing indoor vs. outdoor environments. When aggregating across populations, predicted HEI ratios were significantly smaller than actual mortality ratios, supporting the notion that mortality may not be the best indicator of heat stress effects.