Abstract
Purpose
In older adults with type 2 diabetes (T2D) and hypertension (HTN), cardiac autonomic modulation is markedly attenuated during exercise-heat stress. However, the extent to which this impairment is evident under increasing levels of heat stress remains unknown.
Methods
We examined heart rate variability (HRV), a surrogate of cardiac autonomic modulation, during incremental exercise-heat stress exposures in young (20–30 years) and middle-aged-to-older individuals (50–70 years) without and with T2D and HTN. Thirteen young and healthy (Young, n = 13) and 37 older men without (Older, n = 14) and with HTN (n = 13) or T2D (n = 10) performed 180-min treadmill walking at a fixed metabolic rate (~ 200 W/m2; ~ 3.5 METs) in a differing wet-bulb globe temperature (WBGT; 16 °C, 24 °C, 28 °C, and 32 °C). Electrocardiogram (ECG) and core temperature measurements were recorded throughout. Data were analysed using 5-min averaged epochs following 60-min exercise, which represented the last common timepoint across groups and conditions.
Results
Ageing did not significantly reduce HRV during increasing exercise-heat stress (all p > 0.050). However, T2D and HTN modified HRV during exercise-heat stress such that Detrended Fluctuation Analysis (DFA) α1 (p = 0.012) and the cardiac sympathetic index (p = 0.037) were decreased compared to Older in all except the warmest WBGT condition (32 °C).
Conclusion
Our unique observations indicate that, relative to their younger counterparts, HRV in healthy older individuals is not perturbed during exercise heat-stress. However, relative to their age-matched healthy counterparts, HRV is reduced during exercise-heat stress in individuals with age-associated chronic conditions, indicative of cardiac autonomic dysfunction.
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Data will be made available upon request to the corresponding author.
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Abbreviations
- ANOVA:
-
Analysis of Variance
- CSI:
-
Cardiac sympathetic index
- CVI:
-
Cardiac vagal index
- DFA:
-
Detrended fluctuation analysis
- ECG:
-
Electrocardiogram
- HF power:
-
High-frequency power
- HRV:
-
Heart rate variability
- HTN:
-
Hypertension
- LF power:
-
Low-frequency power
- T2D:
-
Type 2 diabetes
- \({\dot{\text{V}}\text{O}}_{{2{\text{peak}}}}\) :
-
Peak oxygen uptake
- WBGT:
-
Wet-bulb globe temperature
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Acknowledgements
We thank all participants who volunteered for the experiment. We also thank Brian Friesen, Dr. James J. McCormick, Dr. Martin P. Poirier, Audrey Chamberlain, Andre Larocque-Graham, François Beaulieu, Molly Rutherford, Brodie Richards, Madison Schmidt, Mohamed Gemae, Serena Topshee, and Morgan McManus for their assistance with data collection.
Funding
This research was supported by the Government of Ontario and the Canadian Institutes of Health Research (all funds held by Glen P. Kenny). S.R. Notley is supported by a Postdoctoral Fellowship from the Human and Environmental Physiology Research Unit.
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GPK and SRN conceived and designed the study. All authors contributed to the acquisition, analysis, assembly, and interpretation of data. Government of Ontario and the Canadian Institutes of Health Research (all funds held by Glen P. Kenny). JDB, MJM, and GEP completed the statistical analysis. JDB drafted the manuscript. All authors provided critical revisions of the manuscript, approved its final version, and are accountable for all aspects of the work.
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C.L.H is a co-inventor on patents related to physiological waveform assessment and variability analysis. The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. All data are available from the corresponding author upon reasonable request.
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The experiment was approved by the University of Ottawa Health Sciences and Science Research Ethics Board (No: H04-17-05) and agrees with the latest version of the Declaration of Helsinki, except for registration in a database. Written and informed consent was obtained from all volunteers prior to their participation.
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Communicated by Massimo Pagani.
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De Barros, J.A., Macartney, M.J., Peoples, G.E. et al. The impact of age, type 2 diabetes and hypertension on heart rate variability during rest and exercise at increasing levels of heat stress. Eur J Appl Physiol 122, 1249–1259 (2022). https://doi.org/10.1007/s00421-022-04916-4
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DOI: https://doi.org/10.1007/s00421-022-04916-4