Physiological Strain In Older Adults During A Simulated Extreme Heat Event: A Case Study

The likelihood of exposure to hot indoor environments is increasing as climate change exacerbates the frequency and severity of extreme heat events. Recent work from our laboratory demonstrated that older adults sustain greater increases in core temperature during a daylong (9-h) exposure to hot indoor conditions (40 °C) compared to their younger counterparts (PMID:37707866). While these findings represent an important step in quantifying the physiological effects of heat waves on heat-vulnerable individuals, there remains a need for extended studies performed over multiple days, as would occur in a natural heat event. PURPOSE: To evaluate the thermal and cardiovascular responses to a multi-day heatwave simulation in an older adult. METHODS: A 60-year-old male was housed in an environmental chamber for three successive days while exposed to a daytime temperature of 40 °C (45% relative humidity [RH]) for a 10-h period (9:00-19:00) and a nighttime temperature of 36 °C (45% RH) for a 14-h period (19:00-9:00). The participant was permitted to move freely throughout the day but not perform physical activity. A battery of tests assessing cardiovascular and cognitive function, and postural stability were performed in the final 2-h of daytime. Core temperature (rectal; Trec) and heart rate (HR) were measured prior to entry to the heat (ambient temperature; 22 °C) and continuously throughout the trial. RESULTS: Pre-trial resting Trec was 36.5 °C. Prior to the battery of tests (8-h into daytime exposure) Trec reached 37.5 °C, 37.8 °C and 37.5 °C and further increased by 0.2 °C, 0 °C and 0.3 °C at the end of daytime exposure (10-h) for days 1, 2 and 3 respectively. Nighttime was associated with a reduction in Trec, with end nighttime Trec decreasing to 36.9 °C (day 1), 37.0 °C (day 2) and 37.1 °C (day 3). Pre-trial HR was 46 beats per min (bpm), which increased to 66 bpm, 65 bpm, 59 bpm at 8-h, with a further increase of 7 bpm, 12 bpm and 9 bpm at end of daytime (10-h) and a decrease to 48 bpm, 48 bpm, 55 bpm at the end of nighttime for day 1 to 3 respectively. CONCLUSION: We showed that a multi-day exposure to extreme heat is associated with a sustained increase in physiological strain. Notably, the marked elevation in daytime Trec occurred despite a reduction in nighttime temperature closer to resting levels. Supported by: Health Canada HeatADAPT program