Alteration of Inspiratory Muscle Strength Is Related to Change in Deep Breathing Heart Rate Variability in Patients Submitted to Open-Heart Surgery

Abstract

Aim: Despite the reduction of respiratory muscle strength and cardiac autonomic modulation after open-heart surgery has been demonstrated, the association between changes in both variables has not been investigated. This study aimed to determine the correlation between change in inspiratory muscle strength and change in deep breathing heart rate variability in patients submitted to open-heart surgery. Material and Methods: An observational cross-sectional study was conducted among 32 participants aged between 35 and 60 years who were undergoing coronary artery bypass graft and cardiac valve surgery. Inspiratory muscle strength was assessed by measuring maximal inspiratory pressure using a respiratory pressure meter (RPM 01, Micro Medical Ltd., United Kingdom). Deep breathing heart rate variability was collected using a Polar heart rate monitor (Polar Electro Ltd., Finland) during a slow and deep breathing control. Evaluations were performed on the day of admission and discharge. Results: There was statistically significant reduction in maximal inspiratory pressure and deep breathing heart rate variability indices in discharge period (p<0.05). The difference of expiratory/inspiratory ratio and inspiratory-expiratory differences was significantly correlated with the change in maximal inspiratory pressure in both absolute (r=-0.864, p=0.003 and r=-0.841, p=0.004, respectively) and percentages of predicted values (r=-0.868, p=0.003 and r=-0.834, p=0.005, respectively). Conclusion: Inspiratory muscle weakness was related to impair cardiac vagal modulation in patients who had undergone open-heart surgery. The present study could provide rehabilitation targets to improve inspiratory muscle strength and cardiac vagal tone.