Effect of voluntary breathing exercises on stable coronary artery disease in heart rate variability and rate-pressure product: a study protocol for a single blind, prospective randomized controlled trial
Authors: Wu Qing , Liu Lin , Jiang Xin , Hu Yao-Yao , Liang Qiu-Shi , He Zhi-Song , Xue Yuan , Zhu Wei , Tang Zai-Xiang , Hou Yun-Ying , Wang Xiao-Hua , Zhao Qi 
Published: April 2020

Abstract
Background: At present, China has more than 11 million patients with stable coronary heart disease, becoming a major public health problem. The pathological changes of coronary heart disease can lead to dysfunction of cardiac autonomic nervous system, which increases the risk of complications such as malignant arrhythmia (ventricular flutter, ventricular fibrillation, etc.), heart rate, systolic blood pressure, and rate-pressure-product (RPP), which is highly correlated with myocardial oxygen consumption and indirectly reflects myocardial blood supply and oxygen consumption. Although the guidelines recommend that such patients take drugs to reduce heart rate and myocardial oxygen consumption, the clinical control of heart rate is still not ideal. Thus, in this trial, we will use voluntary breathing exercises as the strategy of exercise rehabilitation patients with Stable coronary artery disease（SCAD）, in order to increase the vagus nerve activity and/or reduce the sympathetic nervous activity, help maintain or rebuild the balance of plant nerve system, improve the time domain index of heart rate variability, reduce the burden on the heart, relieve patients' anxiety and other negative emotions. Methods: This is a 6 months single-blind, randomized controlled clinical trial that will be conducted in the First Affiliated Hospital of Soochow University. 140 patients who fill out the Informed Consent Form are registered and randomized 1:1 into the Voluntary Breathing Exercises（VBE）-based clinical trial monitoring group (n = 70) or the Routine follow-up group (n = 70). The VBE-based clinical trial monitoring group is given VBE training on the basis of conventional treatment and health education, while the control group received conventional health education and follow-up. The primary outcome will be measured heart rate variability(HRV) and rate-pressure product (RPP). Secondary outcomes will include changes in self-rating anxiety ccale (SAS), total cholesterol(TC),triglyceride(TG), high density lipoprotein (HDL-C),low density lipoprotein(LDL-C), weight and body mass index (BMI). Discussion: This trial will carry out scientific respiratory exercise for patients with stable coronary heart disease, which belongs to the category of active secondary prevention for patients, and changes from remedial to pre-protective. VBE is easy to operate, and is not limited by time and place. It is very important and meaningful to carry out VBE for patients with SCAD. This study will provide considerable evidence for further large-scale trials and alternative strategies for the rehabilitation nursing of patients with SCAD. Trial registration: This study is registered at Chinese Clinical Trials Registry.gov, ID:1900024043.Registered on 23 June 2019. Keywords: Breathing, Stable coronary artery disease, Heart rate variability, Blood pressure , Myocardial oxygen consumption