Results

A total of 46 individuals were randomized, with 26 assigned to the IS + CR group and 20 to the CR group. Both groups experienced follow‐up losses, related to surgical complications, resulting in a final sample of 32 individuals, as shown in Figure 1. No adverse events or harms related to IS + CR or CR group were observed during the intervention period. All sessions were conducted under physiotherapist supervision and were interrupted if any signs of discomfort or clinical instability occurred; however, no such events were recorded.

FIGURE 1: Study flowchart.

The clinical and sociodemographic characteristics are presented in Table 1. The IS + CR and CR groups did not differ in terms of sex, age, or cardiovascular risk factors. Additionally, no significant differences were observed between the groups in preoperative respiratory muscle strength.

 | CR (n = 15) | IS + CR (n = 17) | p
Sex
Female, % (n) | 27 (4) | 18 (3) | 0.678
Male, % (n) | 73 (11) | 82 (14)
Age (years) | 60.27 ± 7.6 | 64.27 ± 8.5 | 
Weight (kg) | 77.83 ± 12.4 | 76.83 ± 19.2 | 
BMI (kg/m2) | 27.44 ± 3.8 | 26.71 ± 4.9 | 
Type of heart disease
Ischemic, % (n) | 87 (13) | 59 (10) | 0.122
Valvular, % (n) | 13 (2) | 41 (8)
SAH, % (n) | 80 (12) | 76 (13) | 1.0
DM 1, % (n) | 7 (1) | 6 (1) | 1.0
DM 2, % (n) | 40 (6) | 29 (5) | 0.72
Physical inactivity, % (n) | 60 (9) | 53 (9) | 0.735
Arrhythmias, % (n) | 7 (1) | 29 (5) | 0.178
Obesity, % (n) | 27 (4) | 12 (2) | 0.383
Previous cardiac surgery, % (n) | 20 (3) | 6 (1) | 0.319
Dyslipidemia, % (n) | 27 (4) | 29 (5) | 1.0
Smoking, % (n) | 27 (4) | 18 (3) | 0.678
Former smoker, % (n) | 47 (7) | 53 (9) | 1.0
COPD, % (n) | 7 (1) | 6 (1) | 1.0
MI < 90 days, % (n) | 47 (7) | 35 (6) | 0.720
Rest angina, % (n) | 27 (4) | 12 (2) | 0.383
Active endocarditis, % (n) | 0 | 6 (1) | 1.0
Functional classification (NYHA)
NYHA I, % (n) | 27 (4) | 29 (5) | 0.678
NYHA II % (n) | 7 (1) | 24 (4)
NYHA III, % (n) | 7 (1) | 6 (1)
NYHA IV, % (n) | 7 (1) | 0
Respiratory muscle strength
MIP (cmH2O) | 79 ± 32.17 | 74 ± 39.46 | 0.688
% predicted MIP | 80 ± 33.64 | 73 ± 35.44 | 0.618
MEP (cmH2O) | 99 ± 43.43 | 95 ± 54.32 | 0.808
% predicted MEP | 93 ± 38.14 | 87 ± 44.87 | 0.690

Table 2 presents data on surgery, postoperative complications, and hospital length of stay. The IS + CR group exhibited a longer extracorporeal circulation time compared to the CR group, with a large effect size (MD: 22 min; 95% CI: [7.96; 36.04]; d = 1.11). No significant differences were observed between groups in preoperative hospital stay (MD: −2 days; 95% CI: [−8.02; 4.02]; d = −0.23), postoperative hospital stay (MD: −1 day; 95% CI: [−4.71; 2.71]; d = −0.19), or total hospitalization time (MD: −2 days; 95% CI:[−10.37; 6.37]; d = −0.18). Similarly, the incidence of postoperative complications did not differ significantly between groups.

 | CR (n = 15) | IS + CR (n = 17) | p
Type of surgery
CABG, % (n) | 87 (13) | 53 (9) | 0.73
VRS, % (n) | 13 (2) | 35 (6)
CABG + VRS, % (n) | 0 | 12 (2)
ECT, % (n) | 93 (14) | 100 (17) | 0.469
Surgery time (min) | 207 + 37 | 215 ± 24 | 0.593
ECT time (min) | 76 ± 11 | 98 ± 26 | 0.008*
Pneumonia, % (n) | 7 (1) | 18 (3) | 0.603
Atelectasis, % (n) | 40 (6) | 18 (3) | 0.243
Pleural effusion, % (n) | 40 (6) | 53 (9) | 0.502
Fever, % (n) | 20 (3) | 41 (7) | 0.265
Atrial fibrillation, % (n) | 13 (2) | 18 (3) | 1.0
Pulmonary edema, % (n) | 20 (3) | 18 (3) | 1.0
Preoperative hospitalization time (days) | 15 ± 7.9 | 13 ± 9.21 | 0.688
Postoperative hospitalization time (days) | 10 ± 6.78 | 9 ± 2.73 | 0.678
Total hospitalization time (days) | 24 ± 13.36 | 22 ± 9.56 | 0.629

The duration of extracorporeal circulation did not significantly differ according to the occurrence of postoperative complications. Mean extracorporeal circulation time did not differ between patients with and without postoperative pneumonia (98.0 ± 13.9 min vs. 92.9 ± 29.5 min, p = 0.73), atelectasis (95.6 ± 34.2 min vs. 92.7 ± 25.8 min, p = 0.79), pulmonary edema (88.8 ± 23.7 min vs. 94.6 ± 29.1 min, p = 0.65), fever (94.6 ± 24.5 min vs. 93.0 ± 29.9 min, p = 0.88), atrial fibrillation (91.2 ± 29.4 min vs. 94.0 ± 28.2 min, p = 0.84), or pleural effusion (96.8 ± 32.4 min vs. 90.4 ± 23.5 min, p = 0.53). In addition, exploratory analyses showed no significant associations between extracorporeal circulation time and preoperative hospital length of stay (ρ = −0.05, p = 0.77), postoperative hospital length of stay (ρ = 0.20, p = 0.25), or total hospital length of stay (ρ = −0.05, p = 0.77).

Respiratory muscle strength is presented in Figure 2. Inspiratory and expiratory muscle strength decreased from the first postoperative day (POD) until hospital discharge compared with preoperative values in both groups. Inspiratory muscle strength progressively increased from the third POD to hospital discharge compared with the first POD but did not return to preoperative values in either group. Expiratory muscle strength increased only at hospital discharge, without returning to preoperative values in both groups.

FIGURE 2: Respiratory muscle strength data are presented as mean ± standard deviation (SD). Results of the repeated‐measures analysis are presented within each panel (time effect, group effect, and time × group interaction). CR = cardiac rehabilitation; IS + CR = incentive spirometry combined with cardiac rehabilitation; MEP = maximum expiratory pressure; MIP = maximum inspiratory pressure; POD = postoperative day. Statistical symbols indicate within‐group comparisons: *p < 0.05 versus preoperative assessment; †p < 0.05 versus POD 1; ‡p < 0.05 versus POD 3.

Table 3 presents the clinical progression of the groups. During the seven postoperative days, no significant differences were observed in group progression. The effects of CR and IS + CR on the 6MWT and handgrip strength are presented in Table 4. A significant, moderate‐to‐large reduction in functional capacity was observed following surgery (MD: −64.37 m; 95% CI: [−24.1; −104.6]; d = 0.71). Furthermore, the difference in change between groups (interaction effect) was negligible and not statistically significant (MD: 6.23 m; 95% CI: [−74.2; 86.6]; d = 0.07). A generalized estimating equations (GEE) model with an independent working correlation structure and robust standard errors was used to evaluate the effects of time and intervention group on the 6MWD, adjusting for extracorporeal circulation time. The analysis revealed a significant main effect of time, no significant main effect of intervention group, and the time‐by‐group interaction, indicating that the magnitude of change in 6MWD over time was similar between the intervention groups. The covariate extracorporeal circulation time was not significantly associated with 6MWD (Wald χ 2 = 0.022, p = 0.882; β = −0.114, 95% CI: −1.618 to 1.389), suggesting that baseline extracorporeal circulation time did not influence the functional capacity outcome. Overall, adjustment for extracorporeal circulation time did not materially alter the estimated effects of time or intervention group or the time‐by‐group interaction.

 |  | POD 1 | POD 2 | POD 3 | POD 4 | POD 5 | POD 6 | POD 7
STEP 1 | IS + CR % (n) | 76 (13) | 23 (4) | 23 (4) | 0.5 (1) | 12 (2) | 0.5 (1) | 
CR % (n) | 67 (10) | 13 (2) |  | 0.5 (1) |  | 0.5 (1) | 
STEP 2 | IS + CR % (n) | 17 (3) | 53 (9) | 12 (2) | 17 (3) | 0.5 (1) | 12 (2 | 0.5 (1)
CR % (n) | 0.5 (1) | 67 (10) | 33 (5) | 20 (3) | 0.5 (1) |  | 
STEP 3 | IS + CR % (n) |  | 0.5 (1) | 53 (9) | 53 (9) | 23 (4) | 23 (4) | 23 (4)
CR % (n) |  | 13 (2) | 47 (7) | 26 (4) | 26 (4) | 0.5 (1) | 
STEP 4 | IS + CR % (n) |  | 12 (2) |  | 0.5 (1) | 23 (4) | 0.5 (1) | 
CR % (n) |  |  | 20 (3) | 13 (2) | 0.5 (1) | 20 (3) | 20 (3)
STEP 5 | IS + CR % (n) |  |  | 12 (2) | 12 (2) | 17 (3) | 23 (4) | 12 (2)
CR % (n) |  |  |  | 0.5 (1) | 26 (4) | 0.5 (1) | 13 (2)
STEP 6 | IS + CR % (n) |  |  |  | 0.5 (1) | 17 (3) | 12 (2) | 12 (2)
CR % (n) |  |  |  | 13 (2) | 0.5 (1) | 0.5 (1) | 
STEP 7 | IS + CR % (n) |  |  |  |  |  | 0.5 (1) | 
CR % (n) |  |  |  |  | 13 (2) |  | 0.5 (1)
p |  | 0.624 | 0.823 | 0.542 | 0.678 | 0.281 | 0.850 | 0.258

 | CR (n = 15) | IS + CR (n = 17) | p within‐group | p between‐group | p interaction
6MWT
Distance PreOp (m)* | 374 ± 29 | 352 ± 22 | 0.002* | 0.63 | 0.87
Distance on discharge (m)* | 307 ± 22 | 291 ± 43
Handgrip strength
Right PreOp (kgf) | 39 ± 4.73 | 35 ± 4.73 | 0.55 | 0.403 | 0.77
Right PO (kgf) | 35 ± 4.62 | 29 ± 3.70
Left PreOp (kgf) | 37 ± 5.69 | 31 ± 4.92 | 0.135 | 0.354 | 0.943
Left PO (kgf) | 34 ± 5.94 | 27 ± 3.37

No difference in handgrip strength was found after surgery in either group.