Methods

This multicenter, randomized controlled clinical trial with blinded outcome assessment was conducted between May 2019 and October 2023 in the Coronary Intensive Care Unit and Coronary Ward of the University Hospital of Santa Maria (HUSM), the coordinating center of the study, and in the Postoperative Unit (POU) and the Postoperative Inpatient Unit (B2) of the Institute of Cardiology, University Foundation of Cardiology (IC/FUC), the collaborating center. However, data collection was suspended from March 2020 to March 2023 because of the COVID‐19 pandemic. During this period, all non‐essential research activities were halted, and breathing‐exercise interventions were temporarily prohibited. Recruitment resumed only after the hospital authorized the continuation of research activities and permitted the performance of respiratory exercises. Importantly, none of the participants included in the study were diagnosed with COVID‐19 before or after surgery. This was a three‐arm study consisting of the following groups: IS + CR, CR, and a control group. This manuscript specifically compares the effects of IS + CR versus CR. The sample consisted of 46 patients who were randomized through the website http://www.randomization.com to IS + CR (n = 26) or CR (n = 20). The randomization list was generated by an independent researcher who was not involved in participant recruitment, evaluations, or intervention delivery. Allocation was concealed until the commencement of the interventions. Outcome assessors remained blinded to treatment allocation throughout the study. Owing to the nature of the intervention, complete participant blinding was not feasible because participants in the incentive spirometry group actively used the device. To minimize expectancy and placebo effects, all participants were informed that the study compared two postoperative rehabilitation protocols without disclosing the specific study hypotheses or any anticipated superiority of one intervention over the other. Likewise, participants were not informed of the specific objectives associated with each intervention. This partial disclosure approach, commonly used in rehabilitation and behavioral intervention research, was adopted to reduce the potential influence of participants' expectations on study outcomes. All patients received physiotherapy solely within the scope of this study, unless complications or clinical instability required additional intervention. Patients aged 40 years or older, admitted to the cardiovascular unit for valve replacement surgery, CABG, or both, were eligible for this study. Exclusion criteria included patients with a prior diagnosis of chronic heart failure, peripheral neuropathy, musculoskeletal disorders, morbid obesity (BMI > 40 kg/m2), unstable angina, severe coronary trunk injury, severe valvular disease, nephropathy, infectious diseases, cancer patients (post‐chemotherapy), and those whose clinical condition worsened during hospitalization. All participants signed an informed consent form approved by the Research Ethics Committees prior to enrolling in the study. The study followed the recommendations of the Consort Statement and was approved by the Research Ethics Committees of the Federal University of Santa Maria and the Research Ethics Committees of the Institute of Cardiology/University Foundation of Cardiology (IC/FUC) with report numbers 04444018.2.1001.5346 and 04444018.2.2001.5333, respectively. This study was retrospectively registered in the Brazilian Registry of Clinical Trials (ReBEC) under registration number RBR‐8tsjf97.

Patients underwent evaluations and a preoperative physical therapy session to familiarize themselves with the techniques to be used postoperatively, including diaphragmatic breathing, non‐invasive positive pressure ventilation (NIPPV), positive expiratory pressure mask use, deep breathing exercises, and inspiratory muscle training (IMT). Additionally, they received information about the surgery and postoperative care. Data were collected through anamnesis and tests assessing muscle strength, respiratory function, and functional capacity.

Respiratory muscle strength was measured using a manovacuometer (+300 cmH2O to −300 cmH2O) (Pereira 2002). Handgrip strength (HGS) was measured using a digital hand dynamometer (Saehan, SH1001, Korean) (Massy‐Westropp et al. 2004). The six‐minute walk test (6 MWT) was conducted according to the recommendations of the American Thoracic Society (ATS Committee 2002).

Preoperative Interventions

Patients in both the IS + CR and CR groups received information about the surgery, including details on the surgical wound, mediastinal and/or thoracic drains, and other access routes, as well as potential impairments in pulmonary function and postoperative pain. All patients were instructed on how to perform an effective cough postoperatively and were familiarized with the visual analog pain scale, to perform IMT (Turky and Afify 2017) and the use of expiratory positive airway pressure and continuous positive airway pressure masks (Barbas et al. 2014). Additionally, those in the IS + CR group received an IS session (Britto et al. 2014). Details about the preoperative interventions are provided in Supporting Information S1.

Postoperative Interventions

CR was divided into seven steps adapted from Winkelmann et al. (2015). All patients received two daily sessions with a trained physiotherapist who was blinded to the evaluations. This continued until hospital discharge or for up to seven postoperative days. If hospitalization extended beyond this period, patients continued receiving conventional care from the hospital unit. CR was progressively applied according to the patient's clinical condition. Cardiac rehabilitation (CR) was divided into seven steps, adapted from the protocol of Winkelmann et al. (2015), and was performed twice daily. Step 1 (2 METs)—Patient lying in bed. If atelectasis is present, apply noninvasive ventilation (NIV) or positive expiratory pressure (PEP) and perform pulmonary expansion exercises. If pulmonary secretions are present, perform bronchial hygiene maneuvers (flutter, forced expiration technique). Include inspiratory muscle training, active extremity exercises, active‐assisted exercises for the elbows and knees (3 sets of 10 repetitions per exercise), and drain clearance. Step 2 (2 METs)—Patient seated in bed. If atelectasis is present, apply NIV or PEP and perform pulmonary expansion exercises. If pulmonary secretions are present, perform bronchial hygiene maneuvers (flutter, forced expiration technique). Include inspiratory muscle training, active extremity exercises, and active lower limb exercises (quadriceps) (3 sets of 10 repetitions per exercise), along with drain clearance. Step 3 (3–4 METs)—Patient standing. If pulmonary secretions are present, perform bronchial hygiene maneuvers (flutter, forced expiration technique). Include inspiratory muscle training, active exercises for the elbows, knees, and extremities, and active stretching of the lower limbs (quadriceps, adductors, hamstrings, and triceps) (3 sets of 10 repetitions per exercise). Perform stationary marching for 2 minutes and walk 35 m. Step 4 (3‐4 METs)—Patient standing. If pulmonary secretions are present, perform bronchial hygiene maneuvers (flutter, forced expiration technique). Include inspiratory muscle training, active extremity exercises, and active lower limb exercises (flexion, extension, abduction, and adduction) (3 sets of 10 repetitions per exercise). Walk 40–60 m and descend one flight of stairs. Step 5 (3–4 METs)—Patient standing. If pulmonary secretions are present, perform bronchial hygiene maneuvers (flutter, forced expiration technique). Include inspiratory muscle training, active extremity exercises, and active lower limb exercises (flexion, extension, abduction, and adduction) (3 sets of 10 repetitions per exercise). Walk 100–150 m and descend and ascend one flight of stairs. Step 6 (3–4 METs)—Patient standing. If pulmonary secretions are present, perform bronchial hygiene maneuvers (flutter, forced expiration technique). Include inspiratory muscle training, active extremity exercises, and active lower limb exercises (flexion, extension, abduction, and adduction) (3 sets of 10 repetitions per exercise). Walk 150–200 m and descend and ascend two flights of stairs. Step 7 (3–4 METs)—Patient standing. If pulmonary secretions are present, perform bronchial hygiene maneuvers (flutter, forced expiration technique). Include inspiratory muscle training, active extremity exercises, and active lower limb exercises (flexion, extension, abduction, and adduction) (3 sets of 10 repetitions per exercise). Walk 200 m and descend and ascend three flights of stairs.

Progression through the steps depended on patient tolerance. If heart rate increased by more than 20 beats per minute or signs of intolerance appeared, the patient returned to the previous step. Postoperative techniques were taught preoperatively, and inspiratory muscle training began 1–24 hours after extubation, as determined by the physical therapy team. The protocol continued until postoperative day 7 or hospital discharge.

The IS + CR group received IS, as described in the preoperative interventions, combined with CR.

Postoperative Assessments

Inspiratory muscle strength was reassessed on postoperative days 1 (if extubated; otherwise, assessments were performed after extubation), 3, 5, and 7, or at hospital discharge if earlier than day 7. Functional capacity and handgrip strength were measured on postoperative day 7 or at discharge if earlier. Data regarding the duration of invasive mechanical ventilation, length of hospital stay, and postoperative complications—including fever, atrial fibrillation, and PPCs such as pneumonia, atelectasis, pleural effusion, and pulmonary edema—were collected from medical records. PPC diagnoses were established by the attending medical team according to routine institutional clinical practice.

Data Analysis

To detect a minimum difference of 50 m in the 6MWT, with an alpha error of 5% and a power of 80%, the minimum required sample size was calculated to be 12 individuals per group, totaling 24 patients, based on a previous study (Jacob et al. 2023). Descriptive data were presented as means and standard deviations or as absolute and relative frequencies. Normality was assessed using the Shapiro‐Wilk test. Comparisons of clinical and sociodemographic characteristics, surgical data, postoperative complications, and hospital length of stay between intervention groups were conducted using the Chi‐square test (categorical variables), Student's t‐test for independent samples (continuous variables), or the Mann‐Whitney U test (continuous variables), depending on data normality.

Analyses were conducted according to the per‐protocol principle, including only participants who completed the allocated intervention and underwent postoperative outcome assessments. Participants who lost the follow‐up due to postoperative complications or who did not complete the postoperative assessments were excluded from the final analyses. To analyze the effect of the intervention over time (preoperative, postoperative days 1 and 3, and hospital discharge), Generalized Estimating Equations (GEE) were used (Zeger et al. 1988). The same test was applied to assess intervention effects, time effects (preoperative, postoperative days 1 and 3, and hospital discharge), and interaction effects (intervention × time) on manovacuometry parameters (MIP, %MIP, MEP, and % MEP). Bonferroni post hoc tests were applied when necessary. All analyses were performed using SPSS Statistics 26, with a significance level of p < 0.05.