Sample Entropy and Traditional Measures of Heart Rate Dynamics Reveal Different Modes of Cardiovascular Control During Low Intensity Exercise

Matthias Weippert,Annika Rieger,Kristin Behrens,Martin Behrens

doi:10.3390/e16115698

Abstract

Nonlinear parameters of heart rate variability (HRV) have proven their prognostic value in clinical settings, but their physiological background is not very well established. We assessed the effects of low intensity isometric (ISO) and dynamic (DYN) exercise of the lower limbs on heart rate matched intensity on traditional and entropy measures of HRV. Due to changes of afferent feedback under DYN and ISO a distinct autonomic response, mirrored by HRV measures, was hypothesized. Five-minute inter-beat interval measurements of 43 healthy males (26.0 ± 3.1 years) were performed during rest, DYN and ISO in a randomized order. Blood pressures and rate pressure product were higher during ISO vs. DYN (p < 0.001). HRV indicators SDNN as well as low and high frequency power were significantly higher during ISO (p < 0.001 for all measures). Compared to DYN, sample entropy (SampEn) was lower during ISO (p < 0.001). Concluding, contraction mode itself is a significant modulator of the autonomic cardiovascular response to exercise. Compared to DYN, ISO evokes a stronger blood pressure response and an enhanced interplay between both autonomic branches. Non-linear HRV measures indicate a more regular behavior under ISO. Results support the view of the reciprocal antagonism being only one of many modes of autonomic heart rate control. Under different conditions; the identical “end product” heart rate might be achieved by other modes such as sympathovagal co-activation as well.

Highlights

Biological time series like the normal heartbeat-to-heartbeat fluctuation demonstrate complex dynamics [1,2,3,4]
Lindquist et al found a stronger increase of systolic (SBP) and diastolic arterial blood pressure (DBP) during isometric handgrip compared to cycling at comparable heart rate (HR) of 90 bpm [23]
heart rate variability (HRV) sample entropy (SampEn) did not differ between REST and DYN but reached its minimum during ISO

Summary

Introduction

Biological time series like the normal heartbeat-to-heartbeat fluctuation demonstrate complex dynamics [1,2,3,4] Based on their potential to give additional information beyond traditional heart rate variability (HRV) indices [1], nonlinear parameters have been applied for investigating short and long term effects of exercise on heart rate (HR) control [5,6,7,8]. Lindquist et al found a stronger increase of systolic (SBP) and diastolic arterial blood pressure (DBP) during isometric handgrip compared to cycling at comparable HR of 90 bpm [23] Leicht and his associates compared the cardiovascular response to dynamic muscular activity of different muscle groups at 50% maximum HR and concluded that greater HRV may represent increased vagal or dual autonomic modulation [24]

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