Enhancement of sleep stability with Tai Chi exercise in chronic heart failure: Preliminary findings using an ECG-based spectrogram method

Abstract

Objective

To assess the effects of a 12-week Tai Chi exercise program on sleep using the sleep spectrogram, a method based on a single channel electrocardiogram (ECG)-derived estimation of cardiopulmonary coupling, previously shown to identify stable and unstable sleep states.

Methods

We retrospectively analyzed 24-h continuous ECG data obtained in a clinical trial of Tai Chi exercise in patients with heart failure. Eighteen patients with chronic stable heart failure, left ventricular ejection fraction ⩽40% (mean [±standard deviation] age, 59 ± 14 years, mean baseline ejection fraction 24% ± 8%, mean) were randomly assigned to receive usual care (N = 10), which included pharmacological therapy and dietary and exercise counseling, or 12 weeks of Tai Chi training (N = 8) in addition to usual care. Using the ECG-based sleep spectrogram, we compared intervention and control groups by evaluating baseline and 12-week high (stable) and low (unstable) frequency coupling (HFC & LFC, respectively) as a percentage of estimated total sleep time (ETST).

Results

At 12 weeks, those who participated in Tai Chi showed a significant increase in HFC (+0.05 ± 0.10 vs. −0.06 ± 0.09 % ETST, p = 0.04) and significant reduction in LFC (−0.09 ± 0.09 vs. +0.13 ± 0.13 % ETST, p < 0.01), compared to patients in the control group. Correlations were seen between improved sleep stability and better disease-specific quality of life.

Conclusions

Tai Chi exercise may enhance sleep stability in patients with chronic heart failure. This sleep effect may have a beneficial impact on blood pressure, arrhythmogenesis and quality of life.

Introduction

Sleep fragmentation is a well-known clinical feature in patients with heart failure. Standard polysomnographic categorization of sleep quality shows several changes, including reduced total sleep time, reduced sleep efficiency, frequent stage shifts, increased stage 1 non-rapid eye movement (NREM) sleep, reduced to absent slow wave sleep, and a high microarousal index [1]. Insomnia is a common symptom in patients with heart failure. The mechanisms involved include sleep-disordered breathing, poor sleep hygiene, direct (e.g., beta-blocker) and indirect (e.g., diuretic causing nocturia) medication effects, orthopnea/paroxysmal nocturnal dyspnea, and possibly neurohumoral activation itself. Recurrent arousals can severely fragment sleep, contributing to impaired cognitive function and quality of life [2]. In addition, repeated episodes of apnea and hypopnea can have deleterious effects on cardiac physiology and function, causing arterial oxyhemoglobin desaturations, nocturnal hypertensive surges amplified by arousals, triggering of arrhythmias, and an amplification of neurohumoral activation [3], [4]. Improving sleep and sleep-breathing, therefore, is considered an important therapeutic target in the heart failure population.

A relatively new and complementary approach to quantify sleep physiology is the domain of sleep stability. Originally described solely by the electroencephalographic feature of cyclic alternating pattern (CAP and non-CAP) NREM sleep [5], recent work has shown that integrated oscillations of multiple, linked, physiological systems occur during sleep, and that sleep stability may be better described using a more complex, multi-systems approach. For example, features of CAP on electroencephalogram (EEG) are usually associated with temporal instability of respiration, lack of nocturnal blood pressure “dipping,” cyclic bursts of sympathetic activity, lower thresholds for arousals, and non-restorative sleep, a state referred to here as NREM unstable sleep. When the CAP features are absent on EEG (the “non-CAP” state), blood pressure “dipping” occurs, respiration demonstrates temporal stability, and arousal thresholds are elevated, a state referred to here as stable NREM sleep [6].

We developed a method to quantify sleep stability from a single channel electrocardiogram (ECG), mathematically combining heart rate variability (modulated by the autonomic nervous system) and the amplitude modulation of the R-wave associated with mechanical effects of respiration. This method that is based on cardiopulmonary coupling generates a “sleep spectrogram” and provides a visual and numerical estimate of sleep stability and instability. We have previously shown that high-frequency cardiopulmonary coupling during sleep is a feature of stable sleep state and is usually associated with a non-CAP EEG, while low-frequency cardiopulmonary coupling is a feature of unstable sleep state and is usually associated with a CAP EEG [7]. Thus, the sleep spectrographic technique integrates respiration, sleep and autonomic function, three critical variables of state physiology.

This fully-automated ECG-based method also has the advantage of not being constrained by the exact morphology and amplitude of EEG activity during sleep, which can be altered by age, individual differences, skull thickness, medications and disease processes. Arousing stimuli or states (e.g., disease, pain, stress, and certain medications) may contribute to unstable sleep, reducing high- and increasing low-frequency cardiopulmonary coupling during sleep. In contrast, interventions that promote stable sleep may have therapeutic value, particularly in disease states such as heart failure, where sleep fragmentation is so common.

Tai Chi is a meditative exercise with origins in traditional Chinese martial and healing arts. It is widely practiced in Asia, particularly among the elderly, and has gained increasing popularity in the United States. Recent literature has suggested that it may be particularly suitable for the elderly or de-conditioned patient with cardiac disease. Tai Chi incorporates slow-moving, gentle physical activity, balance, and weight shifting, with meditation, relaxation, deep breathing, and imagery. Reported benefits of Tai Chi include increased balance and decreased incidence of falls [8], [9]; increased strength and flexibility [8], [10], [11]; reduced pain and anxiety [12]; improved self-efficacy [13], [14]; improved sleep [15] and enhanced cardiopulmonary function [16], [17], [18], [19]. Improved exercise capacity and quality of life have been reported in patients with heart failure [20], [21].

We hypothesized that Tai Chi may enhance sleep quality and stability in patients with chronic heart failure, and applied the sleep spectrographic technique to 24 h continuous ECG data available from a previously published trial of Tai Chi in heart failure [21].