Pulmonary hypertension (PH) is characterized by a mean pulmonary artery pressure exceeding 20 mmHg, as measured during heart catheterization. In patients with PH, a pulmonary artery wedge pressure of \<15 mmHg and a pulmonary vascular resistance of \>2 Wood Units indicate the presence of pre-capillary pulmonary hypertension (PubMed ID: 36017548). The current clinical classification for pulmonary arterial hypertension (PAH) associated with congenital heart disease (CHD) comprises four subgroups: Eisenmenger syndrome, left-to-right shunts, coincidental or small defects, and postoperative/closed defects (PubMed ID: 30545968). Prognosis varies based on the type and size of the congenital heart defect, the timing of PAH development, and the response to treatment (PubMed ID:33541620). Adults with PAH associated with CHD exhibit symptoms of dyspnea, cyanosis, chest pain, syncope-presyncope, hemoptysis, decreased exercise capacity, and muscle fatigue (PubMed ID: 34211699). A reduction in exercise capacity is the primary clinical feature of PAH (PubMed ID: 25880178). Compared to other CHD patients, in adults with CHD associated with PAH experience lower exercise tolerance, more severe symptoms, and lower survival rates (PubMed ID: 25896865, 17164490, 21777753). ). The decrease in exercise capacity is linked to the risk of hospitalization or mortality, and exercise intolerance is frequent even in asymptomatic cases (PubMed ID: 16061735). While the benefits of physical activity and exercise in managing chronic diseases are well-established, the therapeutic role of exercise for the CHD-associated PAH population has not been sufficiently investigated (PubMed ID: 32201288). The impact of advanced medical treatment on exercise capacity and quality of life seems to be very limited for this population. Therefore, it is emphasized that additional treatment approaches aimed at improving exercise capacity and quality of life may be necessary for this patient group (PubMed ID: 23041100).

One of the significant symptoms observed in patients with PH is muscle fatigue. In these individuals, adenosine triphosphate is anaerobically produced at lower workloads, leading to early lactic acidosis (PubMed ID: 7856531, 11468205). These changes occur in peripheral muscles may cause to exercise limitation (PubMed ID: 27192047). Elevated lactate levels are associated with anaerobic exercise, this may potentially induced by high pulmonary artery pressure during exercise or deconditioning (PubMed ID: 30464443). Blood lactate concentration stands out as one of the frequently assessed parameters in both clinical exercise testing and performance evaluations of athletes (PubMed ID:19885119). The decrease in physical function has been demonstrated to correlate with a decline in emotional well-being and overall quality of life (PubMed ID: 33660435). Furthermore, a study revealed that maximal isometric forearm muscle strength, assessed with a handgrip in PAH patients, was significantly lower than in their healthy counterparts (PubMed ID: 17689235). Another study comparing PAH patients with healthy individuals reported preserved static balance performance but noted a decrease in dynamic balance performance and balance confidence (PubMed ID: 29251653). In a study conducted by Blok et al., utilizing the Short-form 36 Questionnaire to assess quality of life, it was underscored that the decrease in quality of life serves as a determinant of late-term mortality in patients with CHD-related PAH (PubMed ID: 25911012).

In the guidelines published by the European Society of Cardiology, emphasis is placed on the importance of regular exercise for adults with CHD and CHD associated with PAH. The guidelines encourage patients to engage in regular exercise, receive personalized exercise prescriptions, and maintain an active lifestyle. Structured regular exercise is deemed a safe and effective treatment for most patients with CHD (PubMed ID: 32860412, 32860028). ). In the literature, exercise training programs have been implemented for adults with CHD associated with PAH, both in home- and hospital-based settings, with or without supervision (PubMed ID: 23041100, 20136857). There are studies in the literature have explored the effects of aerobic and resistance training, as well as respiratory muscle training (PubMed ID: 23041100, 19604588, 20136857).

The Otago Exercise Program (OEP) is an evidence-based multimodal exercise regimen developed by Campbell and the Otago Medical School of New Zealand in 1997 (PubMed ID: 9366737). Widely utilized during rehabilitation and the postoperative recovery period, the OEP has been studied in various conditions such as osteoarthritis, rheumatoid arthritis, knee prosthesis postoperative rehabilitation, Parkinson's and Alzheimer's disease, stroke, visual impairment, depression, dementia, and cognitive impairment. Recognized as a safe protocol, it is predominantly applied in the literature as a home exercise program for the geriatric population residing in the community. Moreover, recent studies have adapted it to Kinect technologies, presenting virtual exercises, and implemented it as a telehealth service with a home-based exercise program during the Covid-19 pandemic period (PubMed ID: 31118594, 34289524, 19607686, 20458104, 33225343, 28827207, 29958232, 36339194).

Physical activity recommendations for adults with CHD associated with PAH often advise against vigorous intensity exercise in numerous guidelines. The Otago Exercise Program, chosen as an evidence-based multimodal exercise regimen to establish a safe exercise prescription, aligns with literature recommendations. This upcoming study, focusing in adults with CHD associated with PAH a population known for low exercise capacity with recommendations for further research aims to formulate exercise training strategies beneficial for patients.

Our study will be the first investigation examining the effects of the Otago Exercise Program implemented under physiotherapist supervision. With this study to be conducted in adults with congenital heart disease associated pulmonary arterial hypertension, who are reported to have low exercise capacity and further research is recommended, the aim is to develop exercise training strategies that will benefit patients.