Cardiac Adjustments During a Hot and Humid Heatwave Simulation in Older Adults

Abstract

Heatwaves cause disproportionately high morbidity and mortality rates in those aged ≥ 65 years. While the underlying pathologies are typically of cardiovascular origin, the cardiac specific responses to real‐world heatwave conditions are not well‐defined.PurposeWe tested the hypothesis that three hours exposure to a hot and humid heat wave would increase left ventricular systolic contractility (s’) and early propagation velocity of mitral inflow (Vp) and decrease isovolumetric relaxation time (IVRT).MethodsEight healthy older adults (5 female/3 male; 70 ± 4 years; 26 ± 3 kg·m‐2) were exposed to 41°C, 40% humidity (replicating the 1995 Chicago heat wave) for three‐hours, interspersed with seven 5‐minute work bouts at three METS to replicate daily living activities. Core temperature (telemetric pill or rectal thermistor), skin temperature, blood pressure and heart rate were monitored continuously during heating. Water was provided throughout the protocol to minimize dehydration. Echocardiograms were taken at baseline (in a thermoneutral environment) and at three hours into heat stress to assess cardiac function. Pre to post heatwave differences in all variables were compared using paired samples t‐tests.ResultsCore temperature increased (36.7 ± 0.3 to 37.7 ± 0.5°C, p < 0.001), skin temperature increased (34.0 ± 1.1 to 36.2 ± 0.8°C, p = 0.002), heart rate increased (59 ± 9 to 78 ± 18 b·min‐1,p = 0.012), and mean arterial pressure decreased (90 ± 14 to 78 ± 12 mmHg, p= 0.034) from baseline to 3‐hours heat exposure. Left ventricular contractility (s’) increased (8.2 ± 1.0 to 10.4 ± 1.4 cm/s, p = 0.002), while measures of diastolic function were unchanged during heating (p > 0.14 for Vp, IVRT, E, A, E/A, e’, E/e’).ConclusionsOur preliminary findings suggest that humid heatwave exposure increases left ventricular contractility without impacting diastolic function in healthy older adults.