Non-Gaussianity of Low Frequency Heart Rate Variability and Sympathetic Activation: Lack of Increases in Multiple System Atrophy and Parkinson Disease

Ken Kiyono,Yoshiharu Yamamoto,Shin Kwak,Eiichi Watanabe,Junichiro Hayano

doi:10.3389/fphys.2012.00034

Abstract

The correlates of indices of long-term ambulatory heart rate variability (HRV) of the autonomic nervous system have not been completely understood. In this study, we evaluated conventional HRV indices, obtained from the daytime (12:00–18:00) Holter recording, and a recently proposed non-Gaussianity index (λ; Kiyono et al., 2008) in 12 patients with multiple system atrophy (MSA) and 10 patients with Parkinson disease (PD), known to have varying degrees of cardiac vagal and sympathetic dysfunction. Compared with the age-matched healthy control group, the MSA patients showed significantly decreased HRV, most probably reflecting impaired vagal heart rate control, but the PD patients did not show such reduced variability. In both MSA and PD patients, the low-to-high frequency (LF/HF) ratio and the short-term fractal exponent α1, suggested to reflect the sympathovagal balance, were significantly decreased, as observed in congestive heart failure (CHF) patients with sympathetic overdrive. In contrast, the analysis of the non-Gaussianity index λ showed that a marked increase in intermittent and non-Gaussian HRV observed in the CHF patients was not observed in the MSA and PD patients with sympathetic dysfunction. These findings provide additional evidence for the relation between the non-Gaussian intermittency of HRV and increased sympathetic activity.

Highlights

The correlates of indices of long-term ambulatory heart rate variability (HRV) of the autonomic nervous system have not been completely understood
Based on our recent findings that increased λs at scale s = 25 s is associated with increased cardiac mortality risk and that this predictive power is independent of clinical risk factors in congestive heart failure (CHF) and acute myocardial infarction (AMI) patients (Kiyono et al, 2008; Hayano et al, 2011), we evaluated the nonGaussianity index λ25s at s = 25 s, which is at the edge of low frequency (LF) and very low frequency (VLF) ranges
Indices of autonomic function were derived from HRV recordings from multiple system atrophy (MSA), Parkinson disease (PD), and CHF patients as well as from the three separate age-matched control groups

Summary

Introduction

The correlates of indices of long-term ambulatory heart rate variability (HRV) of the autonomic nervous system have not been completely understood. As a marker potentially related to the sympathetic cardiac overdrive, we have recently proposed increased non-Gaussianity of HRV (Kiyono et al, 2008) This form of non-Gaussianity has Abbreviations: AC, acceleration capacity; AMI, acute myocardial infarction; CHF, congestive heart failure; DC, deceleration capacity; DFA, detrended fluctuation analysis; ECG, electrocardiogram; HF, high frequency; HRV, heart rate variability; LF, low frequency; LF/HF, LF-to-HF ratio; MRI, magnetic resonance imaging; MSA, multiple system atrophy; NN, normal-to-normal; PD, Parkinson disease; PDF, probability density function; RMSSD, root mean square of successive difference of NN intervals; SD, standard deviation; SDANN, standard deviation of 5 min averaged NN intervals; SDNN, standard deviation of all NN intervals; ULF, ultra-low frequency; VLF, very low frequency. Hayano et al (2011) reported that the increased non-Gaussianity index, λ25s, which captures intermittent heart rate increments within a scale of 25 s similar to that used in the study by Kiyono et al (2008), is associated with increased cardiac mortality risk in a cohort of acute myocardial infarction (AMI), with the predictive power independent of other HRV indices. As heart rate fluctuations in the scale within a minute are mediated almost exclusively by neural autonomic activities (Camm et al, 1996), but λ25s showed no substantial correlation with vagally mediated HRV indices and the patients taking β-blockers had lower λ25s, Hayano et al (2011) conjectured that the nonGaussianity index in this scale probably captures heart rate fluctuations mediated by intermittent activations of cardiac sympathetic activity, affecting independently the mortality of cardiac patients

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