The effect of cardiac rehabilitation exercises on functional capacity and Ejection fraction in patients after coronary artery bypass graft surgery

Cardiovascular diseases (CVDs) are a main reason of mortality in the world and about 12,775,000 deaths are reported annually due to coronary heart diseases. In addition, around 89,000 deaths occur annually because of these diseases in Iran. Studies have shown that cardiovascular diseases affect the cardiovascular health status of patients. Since most of the daily activities of heart patients are usually performed below the maximum level, most researchers and physicians use sub-maximal exercise tests as a substitute for debilitating cardiopulmonary exercise tests to assess cardiopulmonary function. In this regard, the 6-minute walk (6MWT) test is the most common sub-maximal exercise test to measure cardiorespiratory fitness, and functional capacity. This sub-maximal test measures the maximum distance a person is able to walk in 6 minutes. Studies emphasize the need to perform appropriate interventions to increase the recovery process and quality of life of patients after coronary artery bypass graft surgery. Oliveira et al. (2016) reported in their study that a 6-minute walk test leads to an improvement in oxygen consumption, heart rate, and blood pressure in patients with chronic heart failure for 3 months. In the study of Arbs et al. (2003), it was observed that left ventricular function and injection fraction improved in patients with chronic heart failure after six months of moderate-intensity aerobic exercise. Studies demonstrate that different forms of aerobic exercise cause different physiological adaptations Aerobic exercise such as walking with neuromuscular adaptations simultaneously increases cardiovascular strength, and improves cardiovascular fitness, however there is little information to clarify the mechanism of the impact of this exercise on functional capacity, injection fraction and their changes in the body of patients with coronary artery bypass grafting.

The present study is a quasi-experimental and availablility sampling method. It was performed in the cardiopulmonary rehabilitation department of Fatemeh Zahra Medical Center in Sari. Permission was obtained from the hospital management prior to conducting the study. Necessary moral permission was achieved from the Medical Ethics Committee of Mazandaran University of Medical Sciences (Ethics code 1167, 1398) and was registered with a code of IRCT 20191125045496 N1 in the clinical trial system.Statistical sample of the study includes patients who have undergone coronary artery bypass graft surgery and referred to Fatemeh Zahra Medical Center in Sari for clinical examinations after surgery. The availability sampling method was utilized in this study. Written consent was obtained from all subjects. Finally, the patients were randomly divided into two groups of control (n = 8) and experimental (n = 8).In addition to routine care, the intervention group participated in an 8-week aerobic program. Aerobic exercises performed under the control of a sports medicine specialist, exercise physiologist and nurse for eight weeks (three sessions per week) including exercise with 6 to 14 intensity training (RPE) on a treadmill on a Borg pressure scale for 10 to 20 minutes, next exercise with manual ergometer with intensity of 30 to 50 watts for 8 to 10 minutes and then exercise on stationary bike with intensity of 30 to 50 watts for 8 to 10 minutes. The control group only received daily care under the supervision of a physician for 8 weeks. In both groups, functional capacity and discharge fraction were measured before and after 8 weeks of intervention. The 6-minute walk test (6MWT) was utilized to assess functional capacity and an echocardiographic device (vivid model, made in Germany) was used to measure the discharge fraction. This performance was carried out by a cardiologist at Fatemeh Zahra Hospital in Sari.

Dependent t-test was used to evaluate and compare changes within the group. This test showed that both weight level and body mass index had a significant decrease in the post-exercise period compared to the pre-exercise period in the experimental group (p = 0.033; p = 0.034, respectively), while in the control group, both weight level and body mass index had an insignificant increase in the post-exercise period compared to the pre-exercise period (p = 0.74; p = 0.064, respectively). Also, the results of the intragroup study showed that there was a significant difference between changes in weight and body mass index between the two groups (p = 0.01; p = 0.009, respectively).The results of changes in functional capacity and injection fraction in the intragroup showed that the level of functional capacity and injection fraction in the experimental group increased significantly in the post-exercise period compared to the pre-exercise period (p = 0.001; p = 0.011, respectively), whereas in the control group, their changes were not significant in the post-exercise period compared to the pre-exercise period (p=0.790; p = 0.351, respectively). Also, the results of the intergroup study showed that there was a significant difference between the changes in functional capacity and injection fraction between the two groups (p = 0.001; p = 0.014, respectively).

The present study investigated the effect of cardiac rehabilitation intervention in patients after cardiac bypass surgery. The results showed that there was a significant increase in the functional capacity rehabilitation group and injection fraction. Although it was tried to prevent the effectiveness of some factors on the research results partly by selecting almost identical subjects in the present study, the subjects of the present study were coronary artery bypass graft patients who were nutritionally supervised by a physician, so for the sake of ethical considerations in the study, the diet of the subjects was not under the control of the researcher. In addition, the researcher could not control the cost of energy, the amount of activity, rest and sleep in subjects and so, subsequent researchers should consider these issues as limitations in future research to be able to fully control the variables affecting the research results. Totally, the results of this study showed that eight weeks of moderate intensity aerobic exercise can lead to improve functional capacity and injection fraction in patients after coronary artery bypass graft surgery. Therefore, moderate intensity aerobic exercise can be used as an effective factor to improve functional capacity and injection fraction in patients after coronary artery bypass graft surgery.