In situ physiological and behavioural responses of vulnerable populations during an extreme heat event in Montreal, Quebec 2023: a pilot study

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Introduction: Extreme heat events (EHE) continue to increase in frequency, intensity, and duration, posing a significant health threat to vulnerable populations. Despite the development of heat-health action plans, heat-related injuries during EHE persist with the majority occurring at-home. Although epidemiological evidence has identified vulnerable populations, limited evidence exists to confirm their physiological and behavioural responses within the natural environment. Objective: The objective was to undertake a pilot study to monitor heat-vulnerable populations before and during an EHE and determine whether differences in physiological strain, subjective sleep quality, thermal perception, and thirst, would be detected during the EHE. Methods: Five participants who identified as a member of at least one heat-vulnerable group (67±5 y, 84.3±18.0 kg) participated in this study which ran throughout the summer months in Montreal, Quebec 2023. Using HeatSuite, a multipoint remote data acquisition platform that captures indoor environmental conditions, participants continuously wore a fitness tracker, completed a daily sleep quality assessment and a short questionnaire 4 times a day to quantify their thermal sensation, thermal comfort, and thirst, and recorded their oral temperature, heart rate, and blood pressure at rest 3 times a day (morning, midday, and evening). An EHE, as defined by Environment Canada, occurred Sept. 5th – 7th (max ambient temperature: 30.6±0.6°C; max humidex: 40.7±0.6), and thus the physiological and behavioural data collected are compared to the 3 preceding days (Sept. 2nd – 4th, PRE; max ambient temperature 27.2±2.3°C; max humidex: 34.0±4.6). Results: While all participants had air-conditioning, mean indoor ambient temperature was slightly higher during the EHE (22.5±0.5°C) than PRE (21.4±0.6°C, P=0.03). Total step count increased during the EHE relative to PRE in 4 of 5 participants (+47±83%). Mean oral temperature was higher during the EHE (37.3±1.0°C) compared to PRE (36.7±0.7°C, p<0.05). Mean heart rate was not different during the EHE (82±8 BPM) relative to PRE (81±7 BPM, P=0.32). Mean blood pressure was not different during PRE compared to during the EHE (P>0.38). Subjective sleep quality was lower during the EHE compared to PRE (p<0.05). Participants reported no difference in thermal discomfort (P=0.12) and sensation (P=0.38), however they reported an increased thirst sensation (P=0.03) during the EHE. Conclusion: This pilot study was successful at monitoring physiological and behavioural responses in situ of heat-vulnerable individuals during an EHE. The results suggest that the EHE reduced sleep quality, increased thirst and thermal sensations, resulted in a higher oral temperature, and that participants were more active during the EHE relative to the 3 preceding days. This research is supported by Dr. Ravanelli’s New Frontiers in Research Fund (NFRFR-2021-00247). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.