Autonomic dysfunction in COVID-19 patients receiving mechanical ventilation: A cross-sectional study

ABSTRACT BACKGROUND: Coronavirus disease 2019 (COVID-19) can damage cardiac tissue by increasing troponin levels and inducing arrhythmias, myocarditis, and acute coronary syndrome. OBJECTIVES: To analyze the impact of COVID-19 on cardiac autonomic control in mechanically ventilated intensive care unit (ICU) patients. DESIGN AND SETTING: This cross-sectional analytical study of ICU patients of both sexes receiving mechanical ventilation was conducted in a tertiary hospital. METHODS: Patients were divided into COVID-19-positive (COVID(+)) and COVID-19-negative (COVID(-)) groups. Clinical data were collected and heart rate variability (HRV) records obtained using a heart rate monitor. RESULTS: The study sample comprised 82 subjects: 36 (44%) in the COVID(-) group (58.3% female; median age, 64.5 years) and 46 (56%) in the COVID(+) group (39.1% females; median age, 57.5 years). The HRV indices were lower than the reference values. An intergroup comparison identified no statistically significant differences in the mean normal-to-normal (NN) interval, standard deviation of the NN interval, or root mean square of successive differences in NN intervals. The COVID(+) group had an increased low frequency (P = 0.05), reduced high frequency (P = 0.045), and increased low frequency/high frequency (LF/HF) ratio (P = 0.048). There was a weak positive correlation between LF/HF and length of stay in the COVID(+) group. CONCLUSION: Patients who received mechanical ventilation had lower overall HRV indices. COVID(+) patients who received mechanical ventilation had lower vagal HRV components. These findings likely indicate clinical applicability, as autonomic control impairments are associated with a greater risk of cardiac death.

Effects of Exercise Training on Cardiovascular and Autonomic Parameters in Stroke Survivors: A Systematic Review

Negative changes in cardiovascular and autonomic variables in stroke survivors have encouraged the global scientific community to focus on investigating therapeutic strategies to mitigate stroke damage. The objective of the present study was to describe the effects of exercise training on cardiovascular and autonomic variables in stroke survivors. We used the PICO (population, intervention, control/comparison, and outcome variables) model for the search of articles in PubMed and Physiotherapy Evidence Databases from 2009 to December 2018. The following data were also recorded: type of study, author, year of publication, participants (time after stroke, sample size, and age) and benefits of exercise training. A total of 544 articles were initially selected, of which nine peer-reviewed articles met the search criteria. These nine studies enrolled 611 participants (middle-aged or elderly), and pointed to positive effects of training on maximal oxygen uptake, peak aerobic capacity, 6-minute walk test and resting heart rate. However, more well-controlled studies are needed to confirm the benefits of exercise training on cardiovascular and autonomic variables in this population

Acute response to aerobic exercise on autonomic cardiac control of patients in phase iii of a cardiovascular rehabilitation program following coronary artery bypass grafting

Abstract Objective: The aim of the present study was to investigate the acute response to aerobic exercise on autonomic cardiac control of patients undergoing coronary artery bypass grafting (CABG). Methods: The study sample consisted of eight patients (age: 58.6±7.7 years; body mass index: 26.7±3.5 kg.m2) who underwent a successful CABG (no complications during surgery and/or in the following weeks). To assess heart rate variability (HRV), participants remained in a supine position with a 30-degree head elevation for 20 minutes. Electrocardiographic signal (protocol with three derivations) was collected from 600 Hz sample rate to obtain beat-to-beat intervals (R-R interval). This assessment was performed before, after one hour and after 24 hours of the exercise session. All patients underwent a 35 minutes aerobic exercise session (AES) (low-moderate intensity) on the cycle ergometer. Results: Significant differences were found in the time domain, with positive changes in root mean square of successive RR interval differences (rMSSD) (ms) (parasympathetic component) (one [P=0.017] and 24 hours [P=0.007] post-session). In the frequency domain, we found a significant difference in high frequency (HF) (ms2) (parasympathetic component) (one hour [P=0.048] post-session). The low frequency (LF)/HF ratio (sympathetic and parasympathetic components with a predominance of the sympathetic component) reached statistical significance only 24 hours (P=0.018) post-session. Additionally, the largest effect size was observed only for the LF/HF ratio at one (d=-0.8) and 24 hours (d=-1.3) after one AES. Conclusion: The practice of (acute) aerobic exercise improved autonomic cardiac control in patients undergoing CABG.

Exercise training on cardiovascular diseases: Role of animal models in the elucidation of the mechanisms

Abstract Cardiovascular diseases, which include hypertension, coronary artery disease/myocardial infarction and heart failure, are one of the major causes of disability and death worldwide. On the other hand, physical exercise acts in the preventionand treatment of these conditions. In fact, several experiments performed in human beings have demonstrated the efficiency of physical exercise to alter clinical signals observed in these diseases, such as high blood pressure and exercise intolerance. However, even if human studies demonstrated the clinical efficiency of physical exercise, most extensive mechanisms responsible for this phenomenon still have to be elucidated. In this sense, studies using animal models seem to be a good option to demonstrate such mechanisms. Therefore, the aims of the present study are describing the main pathophysiological characteristics of the animal models used in the study of cardiovascular diseases, as well as the main mechanismsassociated with the benefits of physical exercise.(AU)