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Abstract

We conducted a secondary analysis to investigate whether age-related attenuations in heart rate variability (HRV) worsen during exposure to moderate, dry (36.5°C, 20% RH) or humid (36.5°C, 60% RH) heat conditions that resulted in greater body heat storage among older compared to young participants, and during humid compared to dry heat, regardless of age. Six HRV indices [heart rate (HR), coefficient of variation (CoV), detrended fluctuation analysis: α1, low frequency power, high frequency power, and low/high frequency ratio] were assessed in 10 young (21 ± 3 y) and 9 older (65 ± 5 y) adults for 15-min prior to (baseline), and at the end of a 120-min exposure to dry and humid heat while seated at rest. Our results demonstrated a condition (dry and humid) x time (baseline and end) interaction effect on HR (p = 0.047) such that HR gradually increased during humid heat exposure yet remained similar during dry heat exposure across groups. We also found an age-related attenuation in CoV at baseline for both the dry (young: 0.097 ± 0.023%; older: 0.054 ± 0.016%) and humid (young: 0.093 ± 0.034%; older: 0.056 ± 0.014%) heat conditions (p 0.05). While older adults stored more heat during a brief 120-min exposure to dry heat compared to their young counterparts, this was not paralleled by further age-related impairments in HRV even when body heat storage and cardiovascular strain were exacerbated by exposure to humid heat.

Item Type:	Article
Authors/Creators:	Carrillo, AE and Flouris, AD and Herry, CL and Notley, SR and Macartney, M and Seely, AJE and Wright Beatty, HE and Kenny, GP
Keywords:	aging, autonomic nervous system, heat stress, parasympathetic nervous system, relative humidity, sympathetic nervous system
Journal or Publication Title:	Temperature
Publisher:	Taylor & Francis
ISSN:	2332-8940
DOI / ID Number:	https://doi.org/10.1080/23328940.2019.1684791
Copyright Information:	Copyright 2019 Informa UK Limited, trading as Taylor & Francis Group
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