Safety and Effectiveness of Acceleration Training as Cardiac Rehabilitation Immediately After Open Heart Surgery　― A Pilot Study ―

Abstract

Background: We examined the safety and efficacy of acceleration training (AT) in patients immediately after cardiac surgery.

Methods and Results: This randomized controlled study included patients who underwent open-heart surgery using cardiopulmonary bypass. Of these patients, 31 received regular cardiac rehabilitation (CR) and 39 received AT in addition to regular CR (AT group). AT was provided using a vibration platform (Power Plate^® Pro7^TM and Power plate^® personal; Performance Health System, Chicago, IL, USA). The AT group performed 5 static resistance training sessions: squats, wide stance squats, toe stands, banded squats, and front lunges. Each vibration session lasted 30 s. We evaluated the short physical performance battery, anterior mid-thigh thickness, maximum voluntary isometric contraction of the knee extensors, and serum intercellular adhesion molecule (ICAM-1) and vascular cell adhesion molecule (VCAM-1) concentrations as indicators of endothelial function. The observation period was during hospitalization and lasted approximately 20 days. No adverse events occurred during AT. Ultrasound revealed a significantly lower reduction in muscle mass at discharge in the AT group. No significant differences were observed in ICAM-1 and VCAM-1 concentrations between the 2 groups preoperatively, postoperatively, or at discharge.

Conclusions: AT is considered safe and effective for patients immediately after open-heart surgery. AT, along with regular CR, may prevent skeletal muscle mass loss, muscle weakness, and physical function loss immediately after open-heart surgery.

Acceleration training (AT) is a type of whole-body vibration training that uses a piston vibration machine to produce 3-dimensional vibration along the vertical, frontal, and sagittal axes. The vibrations stimulate repetitive muscle spindle reflexes,¹ leading to increased blood flow to the muscles and improved tissue perfusion.² Previous studies reported that AT improves physical function³ and cardiovascular health.⁴ AT is widely used in various fields, including athlete training, general health, and rehabilitation after orthopedic surgery⁵ and stroke.⁶ Meanwhile, AT is safe for patients with cardiovascular diseases because AT has little influence on cardiovascular responses in healthy adults² and patients with hypertension.⁷ Therefore, AT is used for cardiac rehabilitation, and its effectiveness and safety have been reported.⁸ AT also improves vascular endothelial function,^8,9 which is vital for managing cardiovascular risk, including preventing heart failure.¹⁰ Cardiac rehabilitation is essential after open-heart surgery, and the rehabilitation process after open-heart surgery differs significantly from that performed in internal medicine because of the sternotomy, placement of drains and temporary pacemakers, and wound pain. However, there is no evidence that AT has been implemented in cardiac rehabilitation. Therefore, we conducted this study to clarify the safety and usefulness of AT in cardiac rehabilitation after open-heart surgery.

Methods

This study was approved by the Institutional Review Board of Dokkyo Medical University, Japan (September 12, 2021; Reference no. R-50-10J) and performed in accordance with the Declaration of Helsinki. Before inclusion in this study, details of the study were explained to patients and consent was obtained.

Study Protocol

This randomized controlled study included patients who underwent open-heart surgery using cardiopulmonary bypass. The inclusion criteria were age >18 years and having undergone coronary, valvular, or aortic surgeries using cardiopulmonary bypass. Exclusion criteria were an inability to undergo cardiac rehabilitation after surgery, dialysis, or emergency surgery.

Of the patients who underwent heart and vascular surgery at Dokkyo Medical University Hospital between September 2021 and August 2023, 77 were enrolled in this trial. These patients were randomized using a permuted block method, with 37 patients receiving regular cardiac rehabilitation (Regular group) and 40 receiving AT in addition to regular cardiac rehabilitation (AT group). Two patients from the Regular group who were unable to participate in regular cardiac rehabilitation due to severe cerebral complications were excluded. In addition, 1 patient from the AT group and 4 patients from the Regular group were excluded due to insufficient data. Ultimately, 39 patients in the AT group and 31 patients in the Regular group were included in the study and evaluated (Figure 1).

Figure 1.

Study flow diagram. CPB, cardiopulmonary bypass.

AT was performed after patients were transferred to a general ward and were able to stand up with regular cardiac rehabilitation. Patients in the AT group underwent both AT and regular cardiac rehabilitation. Regular cardiac rehabilitation was performed for approximately 1 h on weekdays. AT was performed thrice weekly during regular cardiac rehabilitation hours, as described below. All data were collected prospectively. The clinical data recorded included age, sex, height, weight, body mass index, left ventricular ejection fraction, comorbidity, preoperative risk, surgical procedure, operative time, cardiopulmonary bypass time, blood transfusion volume, operative complications, serum concentrations of intercellular adhesion molecule (ICAM-1) and vascular cell adhesion molecule (VCAM-1) as markers of endothelial function, B-type natriuretic peptide (BNP), creatinine, estimated glomerular filtration rate (eGFR), albumin, and total protein. A physical examination was performed before surgery and on the day of discharge. Blood tests were performed before and after surgery and at discharge.

AT Interventions

AT was performed using a vibration platform (Power plate^® pro7^TM and Power plate^® personal; Performance Health System, Chicago, IL, USA). In patients with heart failure, exercises of the quadriceps and other lower limb muscles are important.^8,11 All patients were instructed to perform 5 static resistance training exercises, as follows:

• squats – standing with knees bent at 70–80° flexion (Figure 2A)

Figure 2.

Five static resistance training exercises in the acceleration training protocol. (A) Squats; (B) wide stance squats; (C) toe stands; (D) banded squats; (E) front lunges.

• wide stance squats – standing with feet twice shoulder-width apart and knees bent at 70–80° flexion (Figure 2B)

• toe stands – standing on tiptoes (Figure 2C)

• banded squats (hip abduction) – standing with knees bent at 70–80° flexion and a TheraBand fastened around the thighs, which resulted in a resistance load of 2.1 kg when the band was extended to twice its length (Figure 2D)

• front lunges – standing with one foot forward and the other back as far as possible, with the front knee bent to 70–80° flexion (Figure 2E).

Patients were prohibited from wearing shoes when performing the static resistance exercises to eliminate cushioning effects. The vibration platform parameters were as follows: vertical vibrations, a frequency of 30 Hz, and a peak-to-peak amplitude of 3 mm. Each vibration session lasted 30 s, with a 120-s rest interval between sessions. Accordingly, the exercise time with AT was approximately 10 min. Patients undertook AT thrice weekly until discharge. Patients were closely monitored by a physical therapist and instructed to report adverse reactions during AT.

Measurement of the Short Physical Performance Battery (SPPB)

The SPPB was used to assess physical function. The SPPB consists of 3 physical tests, each scored from 0 to 4 for a composite total score of 0–12, namely a balance test, a 4-m walk test, and 5 repeats of the chair stand test. The SPPB can be measured within a few minutes without using special measuring equipment.¹² An association between preoperative SPPB performance and the reacquisition of postoperative walking ability and prognosis has been reported in patients undergoing cardiac surgery.^13,14

Measurement of Maximum Voluntary Isometric Contraction of the Knee Extensors

Maximum voluntary isometric contraction of the knee extensors was determined using a digital handheld dynamometer (#Tas MT-1; ANIMA Co., Ltd., Tokyo, Japan), as described previously.^15,16 Patients performed 2 trials with an interval of at least 2 min between them, with the highest score used in analyses.

Ultrasound Measurement of Muscle Thickness

Ultrasound evaluation of quadriceps muscle thickness was performed at the midpoint of the thigh length using a real-time linear electronic scanner with a 10.0-MHz scanning head and an ultrasound probe (L4-12t-RS Probe; GE Healthcare Japan) and LOGIQ e ultrasound (GE Healthcare Japan), as described previously.^15,16 The scanning head was coated with water-soluble transmission gel to provide acoustic contact without depressing the dermal surface. The subcutaneous adipose tissue–muscle and muscle–bone interfaces were identified from the ultrasound images. The perpendicular distance from the adipose tissue–muscle interface to the muscle–bone interface was considered to represent quadriceps muscle thickness. Anterior thigh muscle thickness was measured in the supine position, twice on each side of the thigh, with the mean value used in analyses.

Statistical Analysis

Continuous variables are presented as the mean±SD and categorical variables are presented as numbers and proportions. All continuous variables were checked for normal distribution using the Shapiro-Wilk test and a normal probability plot. For univariate analyses, normally distributed variables were compared using Student’s t-test or Welch’s t-test, as appropriate. Non-normally distributed variables were compared using the Mann-Whitney U test, and categorical variables were compared using Chi-squared analysis or Fisher’s exact test, as appropriate. Statistical significance was set at two-tailed P values <0.05. All statistical analyses were performed using EZR (Saitama Medical Center, Jichi Medical University, Saitama, Japan), a graphical user interface for R (R Foundation for Statistical Computing, Vienna, Austria). EZR is a modified version of the R commander designed to add statistical functions frequently used in biostatistics.¹⁷

Results

Patient Characteristics

The baseline characteristics of the 39 patients in the AT group and the 31 patients in the Regular group are presented in Table 1. There were no significant differences between the 2 groups in age, sex, body surface area, comorbidity, serum concentrations of total protein, albumin, creatinine, and BNP, eGFR, or Japan SCORE.¹⁸ There were no cases of reoperation in either group.

Table 1.

Preoperative Patient Characteristics

	AT group (n=39)	Regular group (n=31)	P value
Age (years)	69.2±9.7	68.2±9.2	0.503
Male sex	26 (66.7)	21(67.7)	0.999
Body weight (kg)	60.8±15.3	62.0±12.6	0.716
Body surface area (m2)	1.64±0.23	1.64±0.20	0.978
Hypertension	29 (74.4)	24 (77.4)	0.999
Dyslipidemia	26 (66.7)	16 (51.6)	0.228
Diabetes	13 (33.3)	6 (19.3)	0.280
Chronic kidney disease	21 (53.8)	17 (54.8)	0.999
COPD	2 (5.1)	0 (0)	0.499
ABI <0.9	6 (15.4)	2 (6.5)	0.287
Atrial fibrillation	6 (15.4)	7 (22.5)	0.541
NYHA Class III or IV	2 (5.1)	1 (3.2)	0.333
Creatinine (mg/dL)	0.97±0.31	1.02±0.37	0.478
eGFR (mL/min/1.73 m2)	59.0±15.5	57.4±13.5	0.651
Total protein (mg/dL)	7.15±0.68	6.95±0.53	0.185
Albumin (mg/dL)	4.16±0.37	4.00±0.39	0.086
BNP (pg/mL)	207.6±374.1	255.4±368.0	0.601
Left ventricle ejection fraction (%)	56.1±13.4	55.9±13.7	0.947
Japan SCORE (%)	2.98±2.83	2.27±2.11	0.355

Unless indicated otherwise, data are given as the mean±SD or n (%). ABI, ankle-brachial artery pressure index; AT, acceleration training; BNP, B-type natriuretic peptide; COPD, chronic occlusive pulmonary disease; eGFR, estimated glomerular filtration rate; NYHA, New York Heart Association; Regular, regular cardiac rehabilitation.

Operative and clinical outcomes are presented in Table 2. There were no significant differences in operative procedures, operation time, aortic cross-clamp time, bleeding, or blood transfusion between the 2 groups. All patients who underwent coronary artery bypass grafting had one or more great saphenous veins harvested. In addition, the postoperative courses of both groups were similar, and the length of hospital stay in both groups was approximately 20 days.

Table 2.

Operative Characteristics, Clinical Outcomes, and Laboratory Data at Discharge

	AT group (n=39)	Regular group (n=31)	P value
Operative procedures			0.275
Valvular	23 (59.0)	20 (59.0)
Coronary artery bypass grafting	12 (30.8)	5 (16.1)
Thoracic aorta	4 (10.3)	6 (19.4)
MICS	14 (35.9)	11 (35.5)	0.948
Operation time (min)	338.4±75.4	359.3±123.8	0.937
Cardiopulmonary bypass time (min)	182.4±57.4	193.3±72.8	0.822
Aorta cross clamp time (min)	134.0±51.1	147.9±82.5	0.808
Intraoperative bleeding (mL)	1,318.1±776.3	1,519.0±1,112.7	0.535
Red blood cells transfusion (units)	6.8±3.47	8.3±4.67	0.271
Fresh frozen plasma transfusion (units)	11.3±6.65	11.6±7.85	0.814
Platelet concentrates transfusion (units)	15.8±6.92	25.8±15.05	0.051
Complication	1 (2.6)	3 (9.7)	0.310
Reoperation for bleeding	1 (2.6)	2 (6.4)
Pacemaker implantation	0 (0)	1 (3.2)
Intensive care unit stay (days)	2.33±1.87	2.13±2.01	0.435
Hospital stay (days)	20.8±17.3	20.0±10.9	0.720
Left ventricle ejection fraction (%)	53.6±13.5	53.3±10.8	0.918
Creatinine (mg/dL)	0.95±0.38	0.96±0.36	0.864
eGFR (mL/min/1.73 m2)	62.0±16.8	61.5±19.8	0.910
Total protein (mg/dL)	6.46±0.61	6.20±0.34	0.076
Albumin (mg/dL)	3.36±0.33	3.20±0.31	0.040
SBP at prior rehabilitation (mmHg)	106.8±15.8	112.6±14.9	0.113
DBP at prior rehabilitation (mmHg)	68.4±13.1	66.8±11.8	0.595
HR at prior rehabilitation (beats/min)	80.3±11.9	76.8±12.8	0.239
Body weight at discharge (kg)	58.5±14.7	58.8±12.2	0.924

Unless indicated otherwise, data are given as the mean±SD or n (%). CABG, coronary artery bypass grafting; DBP, diastolic blood pressure; MICS, minimally invasive cardiac surgery; SBP, systolic blood pressure. Other abbreviations as in Table 1.

Safety of AT for Post-Cardiovascular Surgery Patients

All patients who underwent AT performed the scheduled training thrice weekly until discharge. No significant changes in vital signs were recorded during AT. Blood pressure and pulse rate after AT were within ±10% of the pre-AT values. No complications related to AT were observed during the follow-up period. There were no complaints of wound pain associated with AT. Patients did not complain of delayed-onset muscle soreness.

Physical Function, Muscle Function, and Muscle Morphological Assessments

The results of physical function, muscle function, and muscle morphological assessments are presented in Table 3. SPPB scores decreased from the preoperative period to discharge in both groups for all parameters (i.e., 4-m walk, chair stand, and balance tests). The 4-m walk score at discharge tended to be higher in the AT than Regular group, although the difference was not statistically significant. There were no significant differences in other SPPB scores. In addition, maximum voluntary isometric contraction of the knee extensors and muscle thickness measured by ultrasound decreased from the preoperative period to discharge in both groups, with no significant differences between the 2 groups.

Table 3.

Short Physical Performance Battery, Functional, and Morphological Assessments

	AT group (n=39)	Regular group (n=31)	P value
SPPB score
Total SPPB score
Preoperative	11.7±0.6	11.3±1.1	0.105
At discharge	11.3±1.0	10.8±2.0	0.170
4-m walk score
Preoperative	3.85±0.37	3.68±0.60	0.244
At discharge	3.72±0.56	3.74±0.58	0.753
Chair stand score
Preoperative	3.85±0.37	3.84±0.45	0.823
At discharge	3.67±0.62	3.39±0.95	0.318
Balance score
Preoperative	3.97±0.16	3.81±0.54	0.100
At discharge	3.92±0.35	3.68±0.70	0.0639
Functional assessment: knee extension (kg)
Preoperative	27.3±12.0	24.3±11.0	0.280
At discharge	23.6±11.0	20.9±8.1	0.275
Morphological assessment: muscle thickness (cm)
Preoperative	2.40±0.55	2.48±0.64	0.603
At discharge	2.27±0.56	2.08±0.59	0.201

Unless indicated otherwise, data are given as the mean±SD. SPPB, Short Physical Performance Battery. Other abbreviations as in Table 1.

We evaluated relative changes in each group between admission and discharge, with results shown in Figure 3. There were no significant differences in relative reductions in SPPB and maximum voluntary isometric contraction of the knee extensors between the 2 groups. In contrast, ultrasound revealed a significantly lower reduction in muscle mass at discharge in the AT group than in the Regular group.

Figure 3.

Relative changes in Short Physical Performance Battery, knee extension, and muscle thickness in the acceleration training (AT) and regular cardiac rehabilitation (Regular) groups from admission to discharge (SD).

Endothelial Function

Results of endothelial function evaluations summarized in Table 4. There were no significant differences in ICAM-1 and VCAM-1 concentrations between the AT and Regular groups preoperatively, postoperatively, or at discharge. In both groups, each parameter tended to increase after surgery using cardiopulmonary bypass and did not decrease by the time of discharge.

Table 4.

Endothelial Function

	AT group (n=39)	Regular group (n=31)	P value
ICAM-1 (ng/mL)
Preoperative	306.6±89.4	345.1±151.8	0.897
Postoperative	398.6±238.0	365.4±109.2	0.594
At discharge	405.3±92.2	434.1±108.2	0.762
VCAM-1 (ng/mL)
Preoperative	747.5±190.4	1,035.5±519.6	0.274
Postoperative	927.5±238.5	1,221.4±483.4	0.274
At discharge	943.6±325.2	1,195.0±560.3	0.131

Unless indicated otherwise, data are given as the mean±SD. ICAM-1, intercellular adhesion molecule-1; VCAM-1, vascular cell adhesion molecule-1. Other abbreviations as in Table 1.

Discussion

In the present study, AT was performed in patients who underwent cardiac or vascular surgery using cardiopulmonary bypass immediately after they could stand for postoperative cardiac rehabilitation. The most important findings of this study are that: AT could be performed safely after open-heart surgery; no patients dropped out due to discomfort from the vibration; and AT resulted in a lower reduction in muscle mass at discharge after open-heart surgery compared with Regular cardiac rehabilitation.

Safety of AT for Patients After Open-Heart Surgery

There are many insertions immediately after open-heart surgery, such as pericardial drains, temporary pacemakers, and central venous catheters. AT uses plates that vibrate at a high speed of 30 Hz, but the effects of this vibration on these insertions are not known. Lung transplantation is one of the most invasive thoracic surgeries. A report on the use of AT for rehabilitation immediately after lung transplantation showed no adverse events or accidental removal of insertions.¹⁹ However, patients must be closely monitored while stepping onto and off the vibrating plates to avoid accidental removal of the inserted object.

Moderate-to-high-intensity resistance training has been found to contribute to muscle strength and increased quality of life in patients with chronic heart failure.²⁰ However, moderate-to-high-intensity resistance training can result in excessive abdominal muscle pressure, increased blood pressure, and an increased pulse rate. AT is effective for maintaining a prescribed posture on a vibrating plate. That is, AT can be performed with less abdominal muscle pressure than resistance training, and training can be performed without causing excessive increases in blood pressure or pulse rate. This suggests that AT benefits patients prone to hemodynamic changes after open-heart surgery.

Less Discomfort Due to Vibration With AT for Patients After Open-Heart Surgery

Generally, vibrations at 5 Hz and below causes severe discomfort, impair visual acuity, and negatively affect manual tracking capability, reaction time, monitoring, and pattern recognition.²¹ AT should be performed at a fast vibration of 30 Hz to avoid adverse events. AT is widely used in various fields, including athlete training, general health, and rehabilitation after orthopedic surgery⁵ and stroke.⁶ However, there are no reports of AT performed early after open-heart surgery. Therefore, it is important to determine whether vibration discomfort makes AT impossible to perform in this group of patients. When introducing AT, patients placed one foot on the vibrating plate to feel the vibration, get used to it, and get a feel for the training vibrations. This enabled smooth AT for the first time, and no patient dropped out of this study due to discomfort from the vibration.

Efficacy of Muscle Thickness Maintenance After Open-Heart Surgery

To evaluate the effect of AT, we measured the thickness of the quadriceps muscles because several studies have reported that quadriceps assessment correlates with activities of daily living in elderly patients.^22,23 We measured the thickness of the quadriceps only in the relaxed state, because many elderly patients have difficulty maintaining muscle contraction during ultrasound examinations and a previous study showed that the thickness of the quadriceps in the relaxed state is useful for evaluation of sarcopenia and activities of daily living.²⁴ We noticed that the maximum voluntary isometric contraction of the knee extensors and muscle thickness decreased after open-heart surgery in both the Regular and AT groups, which may have been associated with decreased SPPB scores as an assessment of physical function.

The decrease in muscle mass early after cardiac surgery in both groups could be related, in part, to proteolysis of the skeletal muscle induced by postoperative elevation of inflammatory cytokine production²⁵ and short-term bed rest. The AT group maintained significantly higher muscle mass than the Regular group. Knee extension strength and SPPB scores tended to be maintained in the AT group. These results suggest that AT is helpful for cardiac rehabilitation after open-heart surgery.

Endothelial Function

Although the findings of the present study suggest the safety and muscle mass maintenance of AT, no improvement in endothelial function was observed in the AT group. Endothelial injury occurring during cardiopulmonary bypass is a significant contributing factor to the development of organ dysfunction, leading to many postoperative complications during cardiac surgery. Counteracting inflammation and endothelial dysfunction during cardiopulmonary bypass is crucial for improving the clinical outcomes of cardiac surgery.²⁶ It has been reported that endothelial function improves immediately after AT or within a few weeks.^8,27 In our study, endothelial function tests could not be performed immediately or several weeks after AT, which would have resulted in no differences between the AT and Regular groups. A more extended training period may have been necessary to improve vascular endothelial function with AT. In addition, functional evaluation using flow-mediated dilatation (FMD) or reactive hyperemia peripheral arterial tonometry may have been necessary to more accurately assess endothelial function.

Study Limitations

The present study has several limitations, primarily due to the short observation period and the small sample size. Although this was a pilot study and could not incorporate a large number of patients, the safety of AT was confirmed; however, its effectiveness should be verified further through future randomized controlled trials. Because FMD correlates with ICAM-1 and VCAM-1,²⁸ we used blood sampling to evaluate endothelial function rather than FMD, which is difficult to perform immediately after open-heart surgery. It is possible that FMD would have been appropriate for a more accurate assessment of endothelial function. Although we demonstrated short-term results of AT in this study, the effects of AT may be more pronounced after long-term training.

Conclusions

AT is considered safe and effective for patients immediately after open-heart surgery. AT, in addition to regular cardiac rehabilitation, may prevent the loss of skeletal muscle mass, muscle weakness, and declines in physical function immediately after open-heart surgery.

Acknowledgments

The authors would like to thank Editage (www.editage.com) for English language editing.

Sources of Funding

This study was supported, in part, by JSPS KAKENHI (Grant no. 21K1127C to S.S.). The funding sources for this study had no role in study design, data collection, analysis, or interpretation. All opinions expressed are those of the authors. No additional external funding was received for the study.

Disclosures

The authors declare that there are no conflicts of interest.

IRB Information

This study was conducted in accordance with the Declaration of Helsinki and was approved by the Ethics Committee of Dokkyo Medical University (Approval no. R-50-10J, September 12, 2021). Informed consent was obtained from all subjects involved in the study. Written informed consent was obtained from the patient for the publication of images in this paper.

Data Availability

The deidentified participant data will be shared on a request basis. Please contact the corresponding author directly to request data sharing. The entire dataset used will be available, including the study protocol. Data will be shared as soon as it is approved by the Institutional Review Board of Dokkyo Medical University, and the data will be available between 9 and 36 months after the publication of this paper. The data will be shared with anyone wishing to access it. Any analyses of the data will be approved, and the data will be shared as an Excel file via email.

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