The impact of threshold-loaded inspiratory muscle training and respiratory biofeedback on preserving inspiratory muscle strength and vital capacity after CABG: a randomized clinical trial.

Objectives: Postoperative pulmonary complications (POPC) are common after cardiac surgeries such as coronary artery bypass grafting (CABG) and are influenced by factors including anesthesia and surgical trauma. Inspiratory muscle training (IMT) with visual biofeedback may mitigate these complications. This study investigates the impact of threshold loading inspiratory muscle training (TL-IMT) combined with respiratory biofeedback on the dynamic strength of inspiratory muscles (S-index) in patients undergoing CABG surgery during their hospitalization phase.

Methods: A single-blind study was conducted with 38 CABG candidates at Shahid Modares Hospital, Tehran. Participants were randomized into two groups: the TL-IMT with biofeedback group and the placebo IMT group. TL-IMT exercises were performed at 30% of maximum dynamic inspiratory strength using the Power Breath K5 device, with visual biofeedback displayed on the screen. The placebo group performed the same exercises at minimal load without biofeedback. Both groups received standard respiratory physiotherapy. Measurements of S-index, peak inspiratory flow (PIF), and vital capacity (VC) were taken before surgery (T1), one day after surgery (T2), and at discharge (T3).

Results: Both groups showed significant changes, with a decrease from T1 to T2 and an increase from T2 to T3. In the study group, T3 values remained the same as at T1, while the placebo IMT group experienced a significant decrease. After surgery, both groups had a drop in the S-index. However, the study group saw more pronounced changes between T3-T2 and T3-T1 compared to the control group, although no significant difference was found between T2-T1. By the time of discharge, the TL-IMT group had higher S-index values than the placebo group, returning to preoperative levels. Additionally, the TL-IMT group showed improvements in PIF and VC.

Conclusion: TL-IMT with visual biofeedback effectively maintains dynamic inspiratory muscle strength and improves key pulmonary parameters in cardiac surgery patients. These findings suggest that integrating TL-IMT with biofeedback can enhance postoperative recovery and reduce the incidence of POPC.