title: Hyperthermia and cardiovascular strain during an extreme heat exposure in young versus older adults.
abstract: We examined whether older individuals experience greater levels of hyperthermia and cardiovascular strain during an extreme heat exposure compared to young adults. During a 3-hour extreme heat exposure (44°C, 30% relative humidity), we compared body heat storage, core temperature (rectal, visceral) and cardiovascular (heart rate, cardiac output, mean arterial pressure, limb blood flow) responses of young adults (n = 30, 19-28 years) against those of older adults (n = 30, 55-73 years). Direct calorimetry measured whole-body evaporative and dry heat exchange. Body heat storage was calculated as the temporal summation of heat production (indirect calorimetry) and whole-body heat loss (direct calorimetry) over the exposure period. While both groups gained a similar amount of heat in the first hour, the older adults showed an attenuated increase in evaporative heat loss (p < 0.033) in the first 30-min. Thereafter, the older adults were unable to compensate for a greater rate of heat gain (11 ± 1 ; p < 0.05) with a corresponding increase in evaporative heat loss. Older adults stored more heat (358 ± 173 kJ) relative to their younger (202 ± 92 kJ; p < 0.001) counterparts at the end of the exposure leading to greater elevations in rectal (p = 0.043) and visceral (p = 0.05) temperatures, albeit not clinically significant (rise < 0.5°C). Older adults experienced a reduction in calf blood flow (p < 0.01) with heat stress, yet no differences in cardiac output, blood pressure or heart rate. We conclude, in healthy habitually active individuals, despite no clinically observable cardiovascular or temperature changes, older adults experience greater heat gain and decreased limb perfusion in response to 3-hour heat exposure.
authors.affiliation: Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Canada; Clinical Epidemiology Program, The Ottawa Hospital Research Institute, Ottawa, Canada.
authors.forename: Glen P
authors.initials: GP
authors.lastname: Kenny
authors.affiliation: Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa , Ottawa, Canada.
authors.forename: Martin P
authors.initials: MP
authors.lastname: Poirier
authors.affiliation: Institute of Sport, Faculty of Education Health and Wellbeing, University of Wolverhampton , Walsall, UK.
authors.forename: George S
authors.initials: GS
authors.lastname: Metsios
authors.affiliation: Faculty of Physical Activity Sciences, University of Sherbrooke , Sherbrooke, Canada.
authors.forename: Pierre
authors.initials: P
authors.lastname: Boulay
authors.affiliation: Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa , Ottawa, Canada.
authors.forename: Sheila
authors.initials: S
authors.lastname: Dervis
authors.affiliation: Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa , Ottawa, Canada.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Friesen
authors.affiliation: Clinical Epidemiology Program, The Ottawa Hospital Research Institute , Ottawa, Canada.
authors.forename: Janine
authors.initials: J
authors.lastname: Malcolm
authors.affiliation: Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Canada; Clinical Epidemiology Program, The Ottawa Hospital Research Institute, Ottawa, Canada; Departments of Medicine, Cardiac Sciences and Community Health Sciences, Faculties of Medicine and Kinesiology, University of Calgary, Calgary, Canada.
authors.forename: Ronald J
authors.initials: RJ
authors.lastname: Sigal
authors.affiliation: Divisions of Thoracic Surgery and Critical Care Medicine, Ottawa Hospital Research Institute, University of Ottawa , Ottawa, Canada.
authors.forename: Andrew J E
authors.initials: AJ
authors.lastname: Seely
authors.affiliation: Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Canada; FAME Laboratory, Department of Exercise Science, University of Thessaly, Trikala, Greece.
authors.forename: Andreas D
authors.initials: AD
authors.lastname: Flouris
keywords: aging; calorimetry; climate change; extreme heat events; heat stress