Heat stress and cardiovascular, hormonal, and heat shock proteins in humans

Abstract

Context: Conditions such as osteoarthritis, obesity, and spinal cord injury limit the ability of patients to exercise, preventing them from experiencing many well-documented physiologic stressors. Recent evidence indicates that some of these stressors might derive from exercise-induced body temperature increases. Objective: To determine whether whole-body heat stress without exercise triggers cardiovascular, hormonal, and extracellular protein responses of exercise. Design: Randomized controlled trial. Setting: University research laboratory. Patients or Other Participants: Twenty-five young, healthy adults (13 men, 12 women; age = 22.1±2.4 years, height = 175.2± 11.6 cm, mass = 69.4±14.8 kg, body mass index = 22.6±4.0) volunteered. Interventions): Participants sat in a heat stress chamber with heat (73° C) and without heat (26° C) stress for 30 minutes on separate days. We obtained blood samples from a subset of 13 participants (7 men, 6 women) before and after exposure to heat stress. Main Outcome Measure(s): Extracellular heat shock protein (HSP72) and catecholamine plasma concentration, heart rate, blood pressure, and heat perception. Results: After 30 minutes of heat stress, body temperature measured via rectal sensor increased by 0.8° C. Heart rate increased linearly to 131.4±22.4 beats per minute (F624 = 186, P< .001) and systolic and diastolic blood pressure decreased by 16 mm Hg (F6,24 = 10.1, P< .001) and 5 mm Hg (F624 = 5.4, P< .001), respectively. Norepinephrine (F112 = 12.1, P =.004) and prolactin (F112 = 30.2, P< .001) increased in the plasma (58% and 285%, respectively) (P< .05). The HSP72 (F1,12 = 44.7, P< .001) level increased with heat stress by 48.7%±53.9%. No cardiovascular or blood variables showed changes during the control trials (quiet sitting in the heat chamber with no heat stress), resulting in differences between heat and control trials. Conclusions: We found that whole-body heat stress triggers some of the physiologic responses observed with exercise. Future studies are necessary to investigate whether carefully prescribed heat stress constitutes a method to augment or supplement exercise. © by the National Athletic Trainers' Association, Inc.