Abstract
Background:
To compare the effects of conventional cardiopulmonary physical therapy (CCPT) and specialized core mobilization exercise (SCME) on cardiopulmonary function and functional difficulties in patients after open-heart surgery.
Methods:
This randomized controlled, single-blind study used repeated-measures analysis of variance to examine time and group interaction effects across multiple postoperative assessment points. A post hoc Tukey test was performed when significant effects were identified. The study was conducted at the Myongji Hospital Cardiac Rehabilitation Center from June 2022 to July 2023 and included 37 patients (mean age = 66.1 ± 11.4 years) who were randomly assigned to the CCPT or SCME group.
Results:
Compared with CCPT, SCME resulted in greater improvements in peak oxygen consumption, metabolic equivalents, forced vital capacity, forced expiratory volume in 1 second, maximal voluntary ventilation (P < .05), and Functional Difficulties Questionnaire scores (P < .01).
Conclusion:
SCME demonstrated superior effects on peak oxygen consumption, selected pulmonary function parameters, and functional thoracic mobility compared with CCPT in patients after open-heart surgery.
Keywords: breathing exercise, cardiac rehabilitation, cardiovascular surgical procedures
1. Introduction
Open-heart surgery is a common procedure involving the dissection of the breastbone and spreading of the ribcage to access the heart for coronary artery bypass surgery (CABG) and valve replacement.[1] Up to 80% post–open-heart surgery (PHS) patients experience reduced cardiopulmonary function (including lung volume and oxygenation) during the initial 3 postoperative days. This results in a 40% to 60% decrease in forced vital capacity (FVC) and forced expiratory volume in the first second (FEV1) in comparison to preoperative values,[2] along with musculoskeletal impairments such as pain, weakness, and limited ribcage mobility.[3] Musculoskeletal issues, particularly pain, weakness, and restricted ribcage movement, can induce paradoxical diaphragm breathing after open-heart surgery, compromising cardiopulmonary function, accumulation of secretions, and gas exchange improvement. Furthermore, decreased cardiopulmonary function limits the peak oxygen consumption (VO2 peak) in PHS patients, creating a vicious cycle.[4]
To mitigate PHS-induced impairments, contemporary cardiopulmonary rehabilitation includes static respiratory exercises that produce limited effects. Brasher et al reported no clinically meaningful difference in postoperative complications, pulmonary function, postoperative hospital stay, oxygen saturation, and pulmonary complications between a walking exercise group and a walking plus diaphragmatic breathing exercise group in PHS individuals.[5] Valenza-Demet et al demonstrated that core-chain breathing was effective in improving chest and ribcage mobility, alleviating pain-related muscle weakness in the chest (e.g., pectoralis, upper trapezius) and ribcage (e.g., intercostalis, diaphragm) muscles commonly observed in PHS individuals.[6]
Based on collective evidence and to overcome the limitations of contemporary cardiopulmonary rehabilitation, we developed a specialized core mobilization exercise (SCME) involving coordinated chest-ribcage core mobilization with subcortical diaphragm breathing and transverse abdominals-EO/IO-multifidus-pelvic floor muscle actions. This specialized exercise is designed to enhance chest and ribcage mobility while unlocking pain-mediated muscle weakness, thereby improving cardiopulmonary function, handgrip strength, and functional thoracic mobility common in PHS individuals.[7]
Recent studies have demonstrated the promising therapeutic effectiveness of SCME on pain, muscle weakness, and limited mobility in neuromuscular and musculoskeletal systems impairment populations.[8] However, the existence of such compatible effects in PHS individuals remains unknown. Therefore, this study aims to compare the differential effects of SCME and conventional cardiopulmonary physical therapy (CCPT) on cardiopulmonary function, handgrip strength, and functional thoracic mobility in acute PHS patients. We hypothesized that SCME would result in greater improvement in cardiopulmonary and functional outcomes compared with CCPT.
2. Methods
2.1. Participants
Among 71 eligible patients admitted for CABG, valve surgery, aortic surgery, or combined procedures at a single medical center, 44 participated in the registered clinical trial (#KCT0008658). All participants provided written informed consent. The trial protocol was approved by the Ethics Committee of Myongji Hospital (no. 2022-05-011). Inclusion criteria entailed CABG, valve surgery, aortic surgery, or combined procedures. Exclusion criteria encompassed: unstable hemodynamic parameters, indicated by systolic arterial pressure <100 mm Hg, diastolic arterial pressure <60 mm Hg, mean arterial pressure <80 mm Hg, and postoperative complications requiring invasive mechanical ventilation or noninvasive ventilation for >24 hours after admission to the intensive care unit. Cognitive impairment, uncooperative behavior, or inability to comprehend or properly utilize the medical device. FVC <10 mL/kg on the first day of post operation (PostOP1) pulmonary function test (PFT). Known pulmonary conditions, recent major cardiac surgery, history of neurological or musculoskeletal disorders, or peripheral vascular diseases. Oxygen saturation <90% with nasal oxygen applied.[9] The demographic and clinical characteristics of the study participants are presented in Table 1.
Table 1.
Demographic and clinical characteristics of the patients (N = 37).
| Parameters | CCPT group (n = 21) | SCME group (n = 16) |
|---|---|---|
| Sex (men/women) | 13/8 | 15/1 |
| Age (yr) | 70.3 ± 11.1 | 60.6 ± 10.2 |
| Height (cm) | 162.9 ± 9.3 | 168.0 ± 8.3 |
| Weight (kg) | 68.9 ± 14.9 | 72.9 ± 13.3 |
| Diagnosis | ||
| Stable angina | 1 | 0 |
| Unstable angina | 6 | 4 |
| NSTEMI | 3 | 3 |
| STEMI | 2 | 3 |
| Heart failure | 1 | 1 |
| Aortic stenosis | 4 | 2 |
| Mitral stenosis | 1 | 0 |
| Aortic regurgitation | 1 | 1 |
| Aortic aneurysm | 0 | 1 |
| Mitral valve regurgitation | 0 | 2 |
| Intracardiac myxoma | 0 | 1 |
| Pleural effusion | 5 | 0 |
| Malignant neoplasm of heart | 2 | 0 |
| Major invasive management | ||
| CABG | 13 | 9 |
| Valve replacement | 7 | 5 |
| Aorta replacement | 0 | 1 |
| Myxoma removal | 0 | 1 |
| LA mass excision | 1 | 0 |
| Past history | ||
| HTN | 13 | 6 |
| DM | 5 | 4 |
| Hyperlipidemia | 7 | 6 |
| None | 7 | 5 |
| Smoking (ex-smoker including) | 9 | 11 |
| Smoking years | 9.3 ± 15.3 | 21.4 ± 16.3 |
| Cig/Day | 7.2 ± 12.1 | 11.9 ± 9.6 |
Data are presented as means ± standard deviations, unless otherwise specified.
CABG = coronary artery bypass graft, CCPT = conventional cardiopulmonary physical therapy, DM = diabetes mellitus, HTN = hypertension, LA = left atrial, NSTEMI = non-ST elevation myocardial infarction, SCME = specialized core mobilization exercise, STEMI = ST elevation myocardial infarction.
2.2. Experimental procedure
The study involved an experimenter-initiated, prospective, randomized, single-blinded endpoint clinical trial design. The participants in the study were randomly assigned to 2 groups (CCPT and SCME, coin flipping by a cardiac rehabilitation nurse). The standardized clinical tests included cardiopulmonary exercise testing (CPET), PFT, handgrip strength, and the functional difficulties questionnaire (FDQ). CPET, handgrip strength, and FDQ were measured by a cardiac rehabilitation nurse, whereas PFT was conducted by an experienced cardiac rehabilitation physical therapist, both blinded to the patients’ group affiliations.
Preoperational (pre-op) day 1: PFT was performed only due to a high risk of heart failure associated with overloading cardiopulmonary function.
Postoperational (post-op) rehabilitation day 1: PFT, handgrip strength, and the FDQ points were measured.
Post-op day 3: CPET was conducted using a symptom-limited protocol with an ergometer ramp of 5 to 15 W. Treadmill evaluations were omitted to administer percutaneous catheter drainage for fluid removal and intravenous drug injections. A 60-minute exercise was conducted according to group-specific intervention protocols. Four participants from the CCPT group and 9 from the SCME group dropped out due to early discharge and refusal to exercise or poor medical condition.
Post-op day 7: PFT, handgrip strength, and FDQ were measured.
One-month post-op: CPET was carried out 1 month after rehabilitation (Fig. 1).
Figure 1.
Timeline of clinical tests. The horizontal line represents the passage of time from pre-surgery to discharge, and the white square box represents the time at which the evaluation was performed. CCPT = conventional cardiopulmonary physical therapy, CPET = cardiopulmonary exercise test, DC = discharge, FDQ = functional disability questionnaire, GW = general ward, ICU = intensive care unit, OP = operation, PFT = pulmonary function test, R1 = rehabilitation day 1, SCME = specialized core mobilization exercise.
2.3. Clinical tests
2.3.1. CPET
CPET was used to evaluate VO2 peak, metabolic equivalents (METs), minute ventilation/carbon dioxide production (VE/VCO2), oxygen consumption/heart rate (VO2/HR), heart rate reserve (HRR), and heart rate recovery in 1 minute (HRR1min; Supplementary Material 1, Supplemental Digital Content). The CPET was performed using a programmable leg ergometer, along with a standard 12-lead continuous electrocardiogram (ECG) monitor (CASE T2100, GE Healthcare) and a Quark gas analysis system (COSMED Omnia 1.6.7). The reliability and validity of CPET as well as the specific standardization procedures are well documented.[10]
2.3.2. PFT
PFT (COSMED Pony FX, Omnia 1.6.7) was used to assess the mechanical performance of the lung, chest wall, respiratory muscles, and airways by measuring the FVC, FEV1, and maximal voluntary ventilation (MVV). The test was performed according to the American Thoracic Society/European Respiratory Society guidelines.[11] The maximum breathing capacity achieved during one continuous 12 to 15-second interval was expressed in L/min. Similar to CPET, the reliability, validity, and specific standardization procedures of PFT are firmly established.[12]
2.3.3. Handgrip strength
Handgrip strength is assessed by measuring the amount of static force a hand can exert while squeezing a dynamometer (JAMAR, Sammons Preston Rolyan). The normal force ranges for ages 60 to 70 are 37.3 to 39.7 kg in men and 22.8 to 24.2 kg in women.[13] The reliability and validity of this assessment method have been affirmed in several studies.[14]
2.3.4. FDQ
The FDQ was used to evaluate the functional performance of the upper extremities and trunk following cardiothoracic surgery. The questionnaire comprises 13 items related to actions that are essential for daily life and involve movements of the thoracic region (Supplementary Material 2, Supplemental Digital Content). The FDQ showed excellent internal consistency (Cronbach alpha coefficient = 0.971) and test–retest reliability (intraclass correlation = 0.918).[15]
2.4. Intervention
CCPT and SCME interventions were consistently provided for 60 minutes, twice a day for 5 days (10 sessions in total). CCPT involves 40 minutes of routine aerobic exercise (30 minutes exercise + 10 minutes rest, warm-up, and cool-down) and 20 minutes of diaphragm breathing exercise whereas SCME comprises 40 minutes of routine aerobic exercise (30 minutes exercise + 10 minutes rest, warm-up, and cool-down) plus 20 minutes of SCME. The intervention intensity and dosage were standardized as follows:
Post-op day 1 to 2: Intensity of routine aerobic exercise, including stationary cycling with adjustable resistance pedals or walking training using a high walker, was set at rating of perceived exertion 13 to ensure patient safety.
Post-op day 3 to 5: Routine aerobic exercise intensity was adjusted to 40% to 60% of VO2 peak based on baseline CPET data. A 5-minute warm-up and cool-down routine consisting of simple movements (alternating arm and leg raises within tolerable range) while sitting was established.[16]
The safety of aerobic exercises was monitored using a portable monitoring equipment under the close supervision of cardiac rehabilitation specialists checking ECGs and oxygen saturation levels.
The exercise intensity was also progressively regulated to achieve the submaximal target heart rate, determined by the heart rate equivalent to 40% to 60% of VO2 peak in CPET results. Patients were monitored and verbally encouraged to reach the established therapeutic goals throughout the sessions.
2.4.1. CCPT
The CCPT intervention included an additional 20-minute practice of diaphragmatic breathing (Supplementary Material 3, Supplemental Digital Content). This was done in a semi-reclined position with proper back and head support to encourage abdominal wall relaxation. One hand was positioned below the front costal margin to monitor rectus abdominal muscle movement, whereas the other hand rested on the upper chest. Participants were directed to inhale gradually and deeply through the nose, holding the breath for 3 seconds. During exhalation, they were instructed to keep the upper chest steady and at ease, enabling the abdomen to ascend, followed by a slow exhale through the mouth. This diaphragmatic breathing routine comprised 3 sets of 5 deep breaths, performed 4 times in a session. Between sessions, participants were advised to maintain regular breathing patterns.[17]
2.4.2. SCME
The SCME intervention included an additional 20-minute practice of SCME (Supplementary Material 4, Supplemental Digital Content). It consisted of 5 exercises, each repeated 10 times per session. Exercises were omitted under the following conditions: severe pain in the surgical area, abnormal ECG necessitating exercise cessation, symptoms of high or low blood pressure (>200 mm Hg systolic and >120 mm Hg diastolic, or <90 mm Hg systolic and <60 mm Hg diastolic), oxygen saturation <85%, and patient refusal.
2.5. Statistical analysis
Statistical analyses were performed using SPSS version 25.0 (IBM Corp.). Descriptive statistics are presented as mean ± standard deviation. Normality of distribution was assessed using the Kolmogorov–Smirnov test. Baseline demographic and clinical characteristics between groups were compared using independent t tests.
A two-way repeated-measures analysis of variance (ANOVA) was conducted separately for each outcome variable to examine the effects of time, group, and their interaction (time × group). For PFT variables (FVC, FEV1, MVV), a 3 (time: pre-op, post-op day 1, post-op day 7) × 2 (group: CCPT, SCME) repeated-measures ANOVA was performed. For CPET variables, a 2 (time: post-op day 3, 1-month follow-up) × 2 (group) repeated-measures ANOVA was conducted. Handgrip strength and FDQ scores were analyzed using a 2 (time: post-op day 1, post-op day 7) × 2 (group) repeated-measures ANOVA.
When significant interaction effects were identified, post hoc pairwise comparisons with Bonferroni correction were performed. Partial eta-squared (ηp2) was calculated as a measure of effect size. Mauchly’s test was used to assess the assumption of sphericity, and Greenhouse–Geisser corrections were applied when violations were detected. Statistical significance was set at P < .05.
Analyses were conducted per protocol due to early postoperative discharge and medical instability in a subset of participants.
3. Results
3.1. Demographic and clinical data
The 4 from the CCPT group and 9 from the SCME group were excluded due to withdrawal, medical complications (dizziness, shortness of breath, resting systolic blood pressure <80, oxygen saturation <85% even with portable oxygen tank). A total of 37 participants (21 in the CCPT group and 16 in the SCME group) comprised the final dataset for statistical analysis (Fig. 2). An independent t test revealed no significant differences, indicating homogeneity in terms of male sex, age, height, smoking years, cigarettes/day, and weight. The Kolmogorov–Smirnov test confirmed the normality assumption for all variables.
Figure 2.
Participant flowchart. This diagram illustrates the randomized allocation, testing points, and dropout rates for each group (CCPT and SCME). CCPT = conventional cardiopulmonary physical therapy, CPET = cardiopulmonary exercise test, FDQ = functional disability questionnaire, OP = operation, PFT = pulmonary function test, SCME = specialized core mobilization exercise.
3.2. CPET outcomes
Significant time effects were observed for VO2 peak (P < .001, ηp2 = 0.60), VO2/HR (P = .003, ηp2 = 0.22), VE/VCO2 slope (P = .002, ηp2 = 0.24), METs (P < .001, ηp2 = 0.65), HRR (P = .007, ηp2 = 0.19), and HRR1min (P < .001, ηp2 = 0.98).
A significant time × group interaction effect was observed for VO2 peak (P = .018, ηp2 = 0.15), indicating a greater improvement in the SCME group compared with the CCPT group. The SCME group increased from 896.0 ± 199.8 mL/min at post-op day 3 to 1291.1 ± 345.1 mL/min at 1 month, whereas the CCPT group increased from 718.1 ± 336.8 mL/min to 936.0 ± 303.2 mL/min.
Similarly, METs demonstrated a significant time × group interaction (P = .022, ηp2 = 0.14). No significant interaction effects were found for VO2/HR (P = .897), VE/VCO2 slope (P = .113), HRR (P = .104), or HRR1min (P = .078; Table 2).
Table 2.
Comparison of CPET variables between the CCPT and SCME groups.
| CCPT (mean ± SD) | SCME (mean ± SD) | P value | |||||
|---|---|---|---|---|---|---|---|
| Post-op (day 3) | Post-op (1 month) | Post-op (day 3) | Post-op (1 month) | Time effect | Time × group | Between groups | |
| VO2 peak (mL/min) | 718.1 ± 336.8 | 936.0 ± 303.2 | 896.0 ± 199.8 | 1291.1 ± 345.1 | .000** ηp2 = 0.60 |
.018* ηp2 = 0.15 |
.036* ηp2 = 0.12 |
| VO2/HR (mL/min) | 7.4 ± 3.0 | 9.1 ± 2.4 | 9.3 ± 2.0 | 10.6 ± 1.8 | .003** ηp2 = 0.22 |
.897 | .077 |
| VE/VCO2 slope | 38.0 ± 6.2 | 36.3 ± 6.6 | 38.3 ± 5.4 | 30.6 ± 6.5 | .002** ηp2 = 0.24 |
.113 | .057 |
| METs | 3.0 ± 1.4 | 4.2 ± 1.3 | 3.4 ± 1.0 | 5.2 ± 1.4 | .000** ηp2 = 0.65 |
.022* ηp2 = 0.14 |
.201 |
| HRR (bpm) | 53.3 ± 17.2 | 45.4 ± 21.3 | 64.6 ± 14.7 | 35.4 ± 23.4 | .007** ηp2 = 0.19 |
.104 | .801 |
| HRR1min (bpm) | 6.9 ± 6.2 | 11.0 ± 6.5 | 5.3 ± 3.5 | 12.6 ± 8.3 | .000** ηp2 = 0.98 |
.078 | .993 |
CCPT = conventional cardiopulmonary physical therapy, CPET = cardiopulmonary exercise testing, HR = heart rate, HRR = heart rate reserve, HRR1min = heart rate recovery in 1 minute, METs = metabolic equivalents, PostOP1M = 1 month later rehabilitation post operation, PostOP3 = third day rehabilitation post operation, SCME = specialized core mobilization exercise, VCO2 = carbon dioxide production slope, VE = minute ventilation, VO2 peak = peak oxygen consumption.
P < .01.
P < .05.
3.3. PFT outcomes
Significant time effects were observed for FVC (P < .001, ηp2 = 0.62), FEV1 (P < .001, ηp2 = 0.57), and MVV (P < .001, ηp2 = 0.37).
Significant time × group interaction effects were identified for FVC (P = .002, ηp2 = 0.18), FEV1 (P = .001, ηp2 = 0.12), and MVV (P < .001, ηp2 = 0.16), demonstrating greater recovery in the SCME group.
The SCME group showed marked improvement from post-op day 1 to post-op day 7 (FVC: 2.0 ± 0.8 L to 2.8 ± 0.9 L; FEV1: 1.5 ± 0.5 L to 2.0 ± 0.6 L; MVV: 67.6 ± 21.4 L/min to 86.9 ± 26.4 L/min), whereas improvements in the CCPT group were modest (FVC: 1.7 ± 0.6 L to 1.8 ± 0.7 L; FEV1: 1.3 ± 0.5 L to 1.3 ± 0.5 L; MVV: 48.0 ± 18.9 L/min to 47.8 ± 21.7 L/min). No significant interaction effect was observed for the FEV1/FVC ratio (P = .455; Table 3).
Table 3.
Comparison of PFT variables between the CCPT and SCME groups.
| CCPT (mean ± SD) | SCME (mean ± SD) | P value | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Pre-op | Post-op (day 1) | Post-op (day 7) | Pre-op | Post-op (day 1) | Post-op (day 7) | Time effect | Time × group | Between groups | |
| FVC (L) | 2.4 ± 0.7 | 1.7 ± 0.6 | 1.8 ± 0.7 | 3.2 ± 0.7 | 2.0 ± 0.8 | 2.8 ± 0.9 | .000** ηp2 = 0.62 |
.002** ηp2 = 0.18 |
.021* ηp2 = 0.14 |
| FEV1 (L) | 1.8 ± 0.7 | 1.3 ± 0.5 | 1.3 ± 0.5 | 2.4 ± 0.6 | 1.5 ± 0.5 | 2.0 ± 0.6 | .000** ηp2 = 0.57 |
.001** ηp2 = 0.12 |
.018* ηp2 = 0.15 |
| MVV (L/min) | 57.1 ± 21.3 | 48.0 ± 18.9 | 47.8 ± 21.7 | 92.6 ± 28.9 | 67.6 ± 21.4 | 86.9 ± 26.4 | .000** ηp2 = 0.37 |
.000** ηp2 = 0.16 |
.001** ηp2 = 0.28 |
| Ratio (%) | 74.1 ± 13.5 | 75.1 ± 14.2 | 73.5 ± 10.4 | 75.7 ± 10.8 | 77.3 ± 9.4 | 72.9 ± 14.4 | .590 | .455 | .573 |
CCPT = conventional cardiopulmonary physical therapy, FEV1 = forced expiratory volume at 1 second, FVC = forced vital capacity, MVV = maximal voluntary volume, PFT = pulmonary function test, PostOP1 = first day rehabilitation post operation, PostOP7 = seventh day rehabilitation post operation, Pre-op = prior to an operation, SCME = specialized core mobilization exercise.
P < .01.
P < .05.
3.4. Handgrip strength outcomes
No significant time effect (P = .485) or time × group interaction effect (P = .129) was detected for handgrip strength. However, a significant between-group difference was observed (P = .049, ηp2 = 0.28), indicating overall higher values in the SCME group (Table 4).
Table 4.
Handgrip strength and FDQ comparison between the CCPT and SCME groups.
| CCPT (mean ± SD) | SCME (mean ± SD) | P value | |||||
|---|---|---|---|---|---|---|---|
| Post-op (day 1) | Post-op (day 7) | Post-op (day 1) | Post-op (day 7) | Time effect | Time × group | Between groups | |
| Handgrip strength (kg) | 26.0 ± 10.3 | 28.7 ± 9.2 | 35.6 ± 8.6 | 34.6 ± 13.1 | .485 | .129 | .049* ηp2 = 0.28 |
| FDQ | 56.3 ± 20.6 | 39.7 ± 14.7 | 57.5 ± 18.4 | 23.6 ± 14.3 | .000** ηp2 = 0.81 |
.000** ηp2 = 0.30 |
.098 |
CCPT = conventional cardiopulmonary physical therapy, FDQ = functional disability questionnaire, PostOP1 = first day rehabilitation post operation, PostOP7 = seventh day rehabilitation post operation, Pre-op = prior to an operation, SCME = specialized core mobilization exercise.
P < .01.
P < .05.
3.5. FDQ outcomes
Significant time (P < .001, ηp2 = 0.81) and time × group interaction effects (P < .001, ηp2 = 0.30) were observed for FDQ scores.
The SCME group showed substantial improvement from 57.5 ± 18.4 at post-op day 1 to 23.6 ± 14.3 at post-op day 7, whereas the CCPT group improved from 56.3 ± 20.6 to 39.7 ± 14.7 (Table 4).
4. Discussion
To the best of our knowledge, this randomized controlled trial is the first to investigate the differential therapeutic effects of SCME and CCPT on cardiopulmonary function, handgrip strength, and functional movement disabilities in individuals following acute open-heart surgery. As anticipated, SCME demonstrated greater improvement in selected cardiopulmonary parameters compared with CCPT, particularly in VO2 peak and pulmonary function variables. SCME was associated with greater improvement in functional thoracic movement, which may reflect reduced pain-related movement limitation.
CPET analysis revealed that SCME was more effective in oxygen uptake than CCPT (82% improvement in VO2 peak, effect size 0.12 medium effects). SCME involves synchronized chest-ribcage movement, subcortical diaphragmatic breathing, and coordination between the transverse abdominal muscles, external and internal obliques, multifidus, and pelvic floor muscles. Initially patients faced breathing difficulties due to the surgical pain on the sternum, chest drainage site (fourth or fifth intercostal space anterior to mid axillary line), and associated paradoxical breathing, which decreased cardiopulmonary function as evidenced by O2 saturation, shortness of breath, dizziness, cyanosis, and HR. SCME significantly alleviated these symptoms compared to CCPT. This is consistent with earlier studies. Hirschhorn et al observed significantly higher (P = .012) oxygen uptake with combining deep breathing exercise and limb/thoracic spine range of motion exercise than that with standard intervention.[18] Manzano et al found significantly increased oxygen-hemoglobin saturation (P = .02) with chest physiotherapy exercises (manual pressure applied on the patient’s chest wall during expiration).[19]
The plausible physiological mechanism at play in this process involves the downward movement of the diaphragm, which expands the chest cavity and reduces internal pressure, facilitating air intake into the lungs because of the resultant difference in external and internal pressure. The natural elasticity of the lungs causes them to contract along with the pleura, generating a negative pressure that aids lung inflation. A weakened diaphragm can limit the available space, hindering air inhalation and increasing pneumonia susceptibility.[20]
VO2/HR, VE/VCO2 slope, HRR, and HRR1min values were no different between the SCME and CCPT groups. However, these variables tend to have lower sensitivity compared to VO2 peak in CPET.
The Fick equation establishes a relationship between VO2, HR, SV, and avO2 difference. The avO2 difference remains relatively stable during incremental exercise, the oxygen pulse (VO2/HR) can serve as an indicator of SV. An increase in VO2/HR (mL/min) indicates an improvement in ventricular efficiency. SCME has more movement compared to CCPT; however, this did not result in a significant change in SV over a week of exercise.
The VE/VCO2 slope data improved in both groups indicating enhanced respiratory efficiency. According to Michaelides et al, draining of pleural fluid leads to a decrease in physiological dead space.[21] In the present study, effective diaphragm movement and coordination of surrounding muscles resulting from SCME reduced ventilation-perfusion mismatching. Among the patients with VE/VCO2 slope above 34, 10 out of 16 SCME patients (62.5%) and 4 out of 21 CCPT patients (19.0%) experienced a decrease in VE/VCO2 slope value to below 34.
Although descriptive trends suggested improved heart rate response in the SCME group, no statistically significant interaction effect was observed. Practicing proper diaphragmatic breathing enhances autonomic function by decreasing sympathetic nervous system activity and boosting baroreflex sensitivity.[22] In the SCME group, the heart rate response of 6 out of 16 individuals (37.5%) changed from <14 to >14, whereas in the CCPT group, 6 out of 21 participants (28.6%) experienced this increase. This indicates enhanced autonomic regulation with SCME, attributed to slow, consistent breathing, which activates the parasympathetic nervous system and leads to a stable heart rate and bodily state.
SCME demonstrated superior pulmonary efficacy compared to CCPT, indicated by large effect sizes for improvements in FVC, FEV1, and MVV from post-op day 1 to post-op day 7. The post hoc analysis result was: post-op day 1 < post-op day 7 < pre-op. The decrease in respiratory volume can be explained by decreased lung compliance due to the accumulation of extracellular fluid and increased vascular volume, as well as closure associated with cell collapse.[23] Mismatch and decrease in thoracic movement contribute to these restrictive changes. Respiratory function is closely related to the coordination between respiratory and peripheral muscle movements, and inefficient coordination between the diaphragm and surrounding muscles reduces respiratory function. Mechanical changes in the lungs, decreased functional residual capacity, and changes in surfactant production occur after open-heart surgery.[24] These factors, combined with a lack of movement, result in an irregular breathing pattern that does not allow for full lung capacity, leading to collapse of lung cells. SCME improves lung expansion in the compromised lungs (caused by fluid in the pleural space) by selectively activating the diaphragm and associated breathing muscles to promote coordination between breathing and movement. This helps with the faster removal of secretions or blood from the pleural space and chest tubes, expatiating the early recovery of cardiopulmonary function. In contrast, CCPT is performed only under the direction of a therapist in static situations and do not consider the coordination between peripheral and surrounding muscles during breathing.
The handgrip strength test revealed no significant differences between the 2 groups before and after exercise. Despite notable improvements in aerobic capacity following the 1-week exercise program, peripheral muscle power exhibited minimal enhancements, indicating the insufficiency of the exercise duration for its development.
The FDQ survey, assessing upper extremity and trunk performance following cardiothoracic surgery pain, showed significant changes with SCME. Approximately 49% patients reported severe pain at rest, 78% had severe pain while coughing, and 62% experienced severe pain during exercise.[25] The most severe pain was related to coughing, movement, turning around, getting out of bed, and deep breathing activities.[26] FDQ, a suitable measure for evaluating functional outcomes specific to the thoracic region, demonstrated the positive impact of SCME on functional thoracic and upper limb mobility issues following open cardiac surgery.
4.1. Study limitations
The present study had some shortcomings that should be considered for future research. First, difference in surgical methods (valvular vs CABG) may have affected the outcome due to unexpected pulmonary edema in the valvular surgical procedure. Nevertheless, randomized sampling and baseline data comparing the valvular and CABG procedures ensured homogeneity.[27] Second, the high-risk surgery led to a notable dropout rate (CCPT 12.5%, SCME 20%), which lowered the sample size and associated type 1 error. However, initial oversampling mitigated this concern. Third, different chest tube removal timings could have affected the cardiopulmonary function and recovery rate during hospitalization. Guizilini et al reported that FVC decreased by 44.87% after surgery in patients with lateral chest tube insertion.[28] This shows that tube insertion can affect the patient’s respiratory function. However, this was beyond control during the respiratory function evaluation. In addition, the relatively small sample size may have limited the power to detect interaction effects for certain CPET-derived indices.
4.2. Clinical perspectives
This study demonstrated the effectiveness of SCME in restoring cardiopulmonary function and functional movement disabilities after acute open-heart surgery. SCME was associated with significant improvements in VO2 peak, METs, pulmonary capacity, and functional thoracic mobility compared with conventional therapy. It is a considerable advancement in physical therapy, focusing on the coordination between the respiratory and peripheral muscles and surpassing the existing CCPT. Thus, our findings have great clinical implications for cardiopulmonary rehabilitation in patients undergoing open-heart surgery.
Author contributions
Conceptualization: Jeong Jae Lee.
Data curation: Jeong Jae Lee.
Formal analysis: Jeong Jae Lee.
Investigation: Jeong Jae Lee.
Project administration: Jeong Jae Lee.
Validation: Jeong Jae Lee.
Writing—original draft: Jeong Jae Lee.
Methodology: Joshua (Sung) H. You.
Supervision: Joshua (Sung) H. You.
Writing—review & editing: Joshua (Sung) H. You.
Abbreviations:
- ANOVA
- analysis of variance
- ATS
- American Thoracic Society
- avO2 difference
- arteriovenous oxygen difference
- CABG
- coronary artery bypass graft
- CCPT
- conventional cardiopulmonary physical therapy
- CPET
- cardiopulmonary exercise testing
- ECG
- electrocardiogram
- ERS
- European Respiratory Society
- FDQ
- functional difficulties questionnaire
- FEV1 =
- forced expiratory volume in 1 second
- FVC
- forced vital capacity
- HR
- heart rate
- HRR
- heart rate reserve
- HRR1min
- heart rate recovery at 1 minute
- ICU
- intensive care unit
- METs
- metabolic equivalents
- MVV
- maximal voluntary ventilation
- PFT
- pulmonary function test
- PHS
- post–open-heart surgery
- Post-Op
- postoperative
- Pre-Op
- preoperative
- SCME
- specialized core mobilization exercise
- SV
- stroke volume
- VE/VCO2
- minute ventilation/carbon dioxide production slope
- VO2 HR
- oxygen pulse
- VO2 peak
- peak oxygen consumption
This work was supported by the National Research Foundation of Korea (NRF), funded by the Korean government (MSIT; grant no. RS-2025-24534569). This research was also supported by the Regional Innovation System & Education (RISE) program through the Gangwon RISE Center, funded by the Ministry of Education (MOE) and Gangwon State (G.S.), Republic of Korea (grant no. 2025-RISE-10-006). In addition, this study was supported by the Assistive Technology Commercialization R&D Project for Independent Living for People with Disabilities and Older Adults, funded by the Ministry of Health and Welfare, Republic of Korea (grant no. RS-2025-02634726).
The authors have no conflicts of interest to disclose.
The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.
Supplemental Digital Content is available in the online version of this article (http://dx.doi.org/10.1097/MD.0000000000048313).
How to cite this article: Lee JJ, You J(S)H. Therapeutic effectiveness of specialized core mobilization exercise on cardiopulmonary function in open-heart surgery patients: A randomized control trial with single-blind study. Medicine 2026;105:19(e48313).
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