Diurnal Variation in Heart Rate Variability before and after Maximal Exercise Testing

Abstract

As heart-rate variability (HRV) is under evaluation in clinical applications, the authors sought to better define the interdependent impact of age, maximal exercise, and diurnal variation under physiologic conditions. The authors evaluated the diurnal changes in HRV 24-h pre- and post-maximal aerobic exercise testing to exhaustion in young (19–25 yrs, n = 12) and middle-aged (40–55 yrs, n = 12) adults. Subjects wore a portable 5-lead electrocardiogram holter for 48 h (24 h prior to and following a maximal aerobic capacity test). Time-, frequency-, time-frequency-, and scale-invariant-domain measures of HRV were computed from RR-interval data analyzed using a 5-min window size and a 2.5-min step size, resulting in a different set of outputs every 2.5 min. Results were averaged (mean ± SE) over four prespecified time periods during the morning, afternoon, evening, and night on Day 1 and Day 2. Diurnal changes in HRV in young and middle-aged adults were compared using a two-way, repeated-measures analysis of variance (ANOVA). Young adults demonstrated higher HRV compared to middle-aged adults during periods of wakefulness and sleep prior to maximal exercise stress testing (i.e., high-frequency power during Day 1: young adults: morning 1862 ± 496 ms², afternoon 1797 ± 384 ms², evening 1908 ± 431 ms², and night 3202 ± 728 ms²; middle-aged adults: morning 341 ± 53 ms², afternoon 405 ± 68 ms², evening 469 ± 80 ms², and night 836 ± 136 ms²) (p < .05). Exercise resulted in reductions in HRV such that multiple measures of HRV were not significantly different between age groups during the afternoon and evening periods. All measures of HRV demonstrated between-group differences overnight on Day 2 (p < .05). Young adults are associated with higher baseline HRV during the daytime. Sleep increases variability equally and proportionally to daytime variability. Given the higher baseline awake HRV and equal rise in HRV during sleep, the change in HRV from sleep to morning with exercise is greater in younger subjects. These physiologic results have clinical significance in understanding the pathophysiology of altered variability in ill patients. (Author correspondence: [email protected])

Keywords:

• Age
• Diurnal variation
• Exercise
• Heart rate
• Heart-rate variation

ACKNOWLEDGMENTS

This research was supported by the Natural Sciences and Engineering Research Council (RGPIN-298159-2004 and RGPIN-298159-2009, grant held by Dr. G. Kenny). Dr. G. Kenny was supported by a University of Ottawa Research Chair Award.

Declaration of Interest: Ms. R. Armstrong, Dr. G. Kenny, and Mr. G. Green have no conflicts of interest to disclose. Dr. A. Seely founded Therapeutic Monitoring Systems in order to commercialize patented Continuous Individualized Monitoring Variability Analysis (CIMVA) technology, with the objective of delivering variability-directed clinical decision support to improve quality and efficiency of care.