Advertisement

European Journal of Applied Physiology

, Volume 114, Issue 4, pp 785–792 | Cite as

Heart rate variability during exertional heat stress: effects of heat production and treatment

  • Andreas D. Flouris
  • Andrea Bravi
  • Heather E. Wright-Beatty
  • Geoffrey Green
  • Andrew J. Seely
  • Glen P. KennyEmail author
Original Article

Abstract

Purpose

We assessed the efficacy of different treatments (i.e., treatment with ice water immersion vs. natural recovery) and the effect of exercise intensities (i.e., low vs. high) for restoring heart rate variability (HRV) indices during recovery from exertional heat stress (EHS).

Methods

Nine healthy adults (26 ± 3 years, 174.2 ± 3.8 cm, 74.6 ± 4.3 kg, 17.9 ± 2.8 % body fat, 57 ± 2 mL·kg·−1 min−1 peak oxygen uptake) completed four EHS sessions incorporating either walking (4.0–4.5 km·h−1, 2 % incline) or jogging (~7.0 km·h−1, 2 % incline) on a treadmill in a hot-dry environment (40 °C, 20–30 % relative humidity) while wearing a non-permeable rain poncho for a slow or fast rate of rectal temperature (T re) increase, respectively. Upon reaching a T re of 39.5 °C, participants recovered until T re returned to 38 °C either passively or with whole-body immersion in 2 °C water. A comprehensive panel of 93 HRV measures were computed from the time, frequency, time–frequency, scale-invariant, entropy and non-linear domains.

Results

Exertional heat stress significantly affected 60/93 HRV measures analysed. Analyses during recovery demonstrated that there were no significant differences between HRV measures that had been influenced by EHS at the end of passive recovery vs. whole-body cooling treatment (p > 0.05). Nevertheless, the cooling treatment required statistically significantly less time to reduce T re (p < 0.001).

Conclusions

While EHS has a marked effect on autonomic nervous system modulation and whole-body immersion in 2 °C water results in faster cooling, there were no observed differences in restoration of autonomic heart rate modulation as measured by HRV indices with whole-body cold-water immersion compared to passive recovery in thermoneutral conditions.

Keywords

Exercise-induced hyperthermia EHS Heart rate variability HRV Core temperature Hyperthermia 

Abbreviations

ANS

Autonomic nervous system

ECG

Electrocardiogram

EHS

Exertional heat stress

FH + C

Fast heating with whole-body cooling session

FH + N

Fast heating with natural recovery session

HRV

Heart rate variability

NN

Normal-to-normal heart rate variability

RMSSD

Root mean square of differences of successive normal-to-normal intervals

R–R interval

Time between two consecutive R waves in the electrocardiogram

SH + C

Slow heating with whole-body cooling session

SH + N

Slow heating with natural recovery session

Tre

Rectal temperature

\( \dot{V}{\text{O}}_{{ 2 {\text{peak}}}} \)

Peak oxygen consumption

Notes

Acknowledgments

This research was supported by the Natural Sciences and Engineering Research Council (RGPIN-298159-2009) and Canada Foundation for Innovation—Leaders Opportunity Fund (22529); (grants held by Dr. Glen Kenny). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The authors wish to thank the lab members of the Human and Environmental Physiology Research Unit for their assistance during data collection and the time and effort of all the participants.

Conflict of interest

Andrew J. E. Seely is the founder and Chief Science Officer, and Geoffrey Green is the Product Manager of Therapeutic Monitoring Systems (TMS). TMS aims to commercialize patented continuous individualized multi-organ variability analysis (CIMVA) technology, with the objective of delivering variability-directed clinical decision support to improve quality and efficiency of care. All the other authors have no conflicts of interest to disclose.

References

  1. Armstrong LE, Maresh CM, Crago AE, Adams R, Roberts WO (1994) Interpretation of aural temperatures during exercise, hypothermia, and cooling therapy. Med Exerc Nutr Health 3:9–16Google Scholar
  2. Armstrong LE, Casa DJ, Millard-Stafford M, Moran DS, Pyne SW, Roberts WO (2007) American College of Sports Medicine position stand. Exertional heat illness during training and competition. Med Sci Sports Exerc 39(3):556–572PubMedCrossRefGoogle Scholar
  3. Balady GJ, Chaitman B, Driscoll D, Foster C, Froelicher E, Gordon N, Pate R, Rippe J, Bazzarre T (1998) Recommendations for cardiovascular screening, staffing, and emergency policies at health/fitness facilities. Circulation 97(22):2283–2293PubMedCrossRefGoogle Scholar
  4. Bravi A, Longtin A, Seely AJ (2011) Review and classification of variability analysis techniques with clinical applications. Biomed Eng Online 10:90PubMedCentralPubMedCrossRefGoogle Scholar
  5. Brenner IK, Thomas S, Shephard RJ (1997) Spectral analysis of heart rate variability during heat exposure and repeated exercise. Eur J Appl Physiol Occup Physiol 76(2):145–156PubMedCrossRefGoogle Scholar
  6. Brenner IK, Thomas S, Shephard RJ (1998) Autonomic regulation of the circulation during exercise and heat exposure. Inferences from heart rate variability. Sports Med 26(2):85–99PubMedCrossRefGoogle Scholar
  7. Buchheit M, Peiffer JJ, Abbiss CR, Laursen PB (2009) Effect of cold water immersion on postexercise parasympathetic reactivation. Am J Physiol Heart Circ Physiol 296(2):H421–H427PubMedCrossRefGoogle Scholar
  8. Carrillo AE, Cheung SS, Flouris AD (2013) Autonomic nervous system modulation during accidental syncope induced by heat and orthostatic stress. Aviat Space Environ Med 84(7):722–725PubMedCrossRefGoogle Scholar
  9. Casa DJ, Armstrong LE (2003) Exertional heatstroke. A medical emergency. In: Armstrong LE (ed) Exertional heat illnesses. Human Kinetics, Champaign, pp 230–234Google Scholar
  10. Casa DJ, Armstrong LE, Ganio MS, Yeargin SW (2005) Exertional heat stroke in competitive athletes. Curr Sports Med Rep 4(6):309–317PubMedCrossRefGoogle Scholar
  11. Casa DJ, McDermott BP, Lee EC, Yeargin SW, Armstrong LE, Maresh CM (2007) Cold water immersion: the gold standard for exertional heatstroke treatment. Exerc Sport Sci Rev 35(3):141–149PubMedCrossRefGoogle Scholar
  12. Casa DJ, Armstrong LE, Kenny GP, O’Connor FG, Huggins RA (2012) Exertional heat stroke: new concepts regarding cause and care. Curr Sports Med Rep 11(3):115–123PubMedCrossRefGoogle Scholar
  13. CSEP (2002) Physical activity readiness-questionnaire, Canadian Society for Exercise PhysiologyGoogle Scholar
  14. Dinas PC, Koutedakis Y, Flouris AD (2013) Effects of active and passive tobacco cigarette smoking on heart rate variability. Int J Cardiol 163(2):109–115Google Scholar
  15. Faul F, Erdfelder E, Lang AG, Buchner A (2007) G*Power 3: a flexible statistical power analysis program for the social, behavioral, and biomedical sciences. Behav Res Methods 39(2):175–191PubMedCrossRefGoogle Scholar
  16. Flouris AD, Cheung SS (2006) Design and control optimization of microclimate liquid cooling systems underneath protective clothing. Ann Biomed Eng 34(3):359–372PubMedCrossRefGoogle Scholar
  17. Flouris AD, Cheung SS (2009) Influence of thermal balance on cold-induced vasodilation. J Appl Physiol 106(4):1264–1271PubMedCrossRefGoogle Scholar
  18. Flouris AD, Cheung SS (2010) Thermometry and calorimetry assessment of sweat response during exercise in the heat. Eur J Appl Physiol 108(5):905–911PubMedCrossRefGoogle Scholar
  19. Leicht AS, Sinclair WH, Patterson MJ, Rudzki S, Tulppo MP, Fogarty AL, Winter S (2009) Influence of postexercise cooling techniques on heart rate variability in men. Exp Physiol 94(6):695–703 (expphysiol)PubMedCrossRefGoogle Scholar
  20. Pounds S, Cheng C (2006) Robust estimation of the false discovery rate. Bioinformatics 22(16):1979–1987PubMedCrossRefGoogle Scholar
  21. Proulx CI, Ducharme MB, Kenny GP (2003) Effect of water temperature on cooling efficiency during hyperthermia in humans. J Appl Physiol (1985) 94(4):1317–1323Google Scholar
  22. Siri WE (1956) The gross composition of the body. Adv Biol Med Phys 4:239–280PubMedCrossRefGoogle Scholar
  23. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology (1996) Heart rate variability: standards of measurement, physiological interpretation and clinical use. Circulation 93(5):1043–1065CrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • Andreas D. Flouris
    • 1
  • Andrea Bravi
    • 2
  • Heather E. Wright-Beatty
    • 3
  • Geoffrey Green
    • 2
  • Andrew J. Seely
    • 2
  • Glen P. Kenny
    • 3
    Email author
  1. 1.FAME LaboratoryCentre for Research and Technology HellasTrikalaGreece
  2. 2.Divisions of Thoracic Surgery and Critical Care MedicineOttawa Hospital-General Campus, Ottawa Health Research InstituteOntarioCanada
  3. 3.Human and Environmental Physiology Research Unit, Faculty of Health Sciences, School of Human KineticsUniversity of OttawaOttawaCanada

Personalised recommendations