Improvement in oxygen dynamics after 3 months of home-based respiratory muscle rehabilitation in a patient with complex severe pulmonary hypertension: A case report

A 26-year-old woman with congenital heart disease, postatrial septal defect repair, postarterial catheter ligation, hypoxia-associated pulmonary hypertension, and reduced right heart function, which manifested as a severe decrease in activity tolerance, chest tightness and shortness of breath, and easy fatigue of breathing, was treated with oxygen, targeting medications such as anisentan, tadalafil, remodulin, and diuretic potassium supplementation to enhance cardiac function, and then her symptoms were slightly improved compared with the previous ones. She was guided with in-hospital respiratory training to the extent that the patient could tolerate it and then was discharged from the hospital to have a home-based respiratory rehabilitation for a period of 3 months. The training plan was as follows: (i) Respiratory muscle function test: the patient's resting maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) were assessed by the respiratory trainer equipment, and the respiratory muscle weakness/invulnerability was defined as a measured maximal pressure value less than 80 cmH₂O according to the ERS guidelines.¹ (ii) Respiratory muscle training impedance progression: first month, 30% of the MIP and MEP of this test, 30 repetitions/day, 5–7 days/week for 1 month; second month, reassessment of respiratory muscle strength with impedance of 35% of the MIP and MEP of this test, 30 repetitions/day, 5–7 days/week for 1 month; and month 3, reassessment of respiratory muscle strength with impedance of MIP and 40% of MEP, 30 times/day, 5–7 days/week for 1 month. During the period of home respiratory rehabilitation, this patient did not experience any adverse hazardous events. (1) After 3 months of training, this patient's respiratory muscle strength improved, including a significant increase in MIP from 43 to 53 cmH₂O and a slight increase in MEP from 53 to 57 cmH₂O; peak inspiratory flow rate decreased from 2.77 to 3.50 L/s, and peak expiratory flow rate decreased from 3.01 to 2.57 L/s. (2) This patient's oxygen saturation improved with oxygen (91% vs. 94%) and her heart rate decreased significantly without oxygen (102 vs. 90 bpm) compared to before training (91% vs. 94%). Additionally, her heart rate was significantly lower (102 vs. 90 bpm), and oxygen saturation was significantly better (83% vs. 89%) without oxygen than it was 3 months prior. (3) Subjective symptoms improved, with the patient initially completing a training session with a Borg score of up to 12/20. After training, she completed the same session with a Borg score of 9–10/20. (4) Weakness improved. Before training, the patient experienced more than moderate shortness of breath with minimal activity and needed a wheelchair while in an oxygenated state. After the training, she could go up and down three staircases or walk on the flat ground for 3–4 min with much less perceived dyspnea.

Respiratory muscle weakness is common in patients with pulmonary arterial hypertension;² patients with respiratory muscle weakness are prone to increased respiratory muscle work, which causes respiratory muscle fatigue, alters respiratory responses, and ultimately leads to exercise intolerance. Respiratory muscle training can increase inspiratory muscle strength and endurance. The abnormal performance associated with respiratory muscle weakness can be partially counteracted, thus improving exercise capacity. In addition to exercise rehabilitation in the conventional sense, more rehabilitation modalities have been shown to improve exercise tolerance in patients with cardiovascular disease, and respiratory muscle rehabilitation can be an important modality for home rehabilitation due to its simplicity and ease of implementation.³

We have seen significantly improved respiratory muscle strength, functional capacity, as well as dyspnea and fatigue in this complex pulmonary arterial hypertension patient after 3 months of respiratory muscle rehabilitation training, which is consistent with the findings of Saglam M et al.⁴ In addition to this, this patient had increased peripheral oxygen saturation and decreased heart rate after training compared to pretraining. Although both MIP and MEP improved in this patient, the respiratory muscle strength was still lower than the normal expected value, which indicated that the patient still had residual inspiratory muscle weakness, which may be related to the fact that sarcopenia is common in patients with pulmonary arterial hypertension, where respiratory muscle damage can be more severe than skeletal muscle damage, making it more difficult to improve the respiratory muscle strength.^4-7 Also, the increased oxygen saturation and decreased heart rate in patients may be related to the fact that respiratory muscle training improves the efficiency of the patient's respiratory muscle⁶ and results in a decrease in the cardiac output required to do the work of breathing to maintain ventilation under the same conditions and some improvement in oxygen kinetics.^{4, 8, 9} It has also been shown that increasing inspiratory muscle strength increases the ventilatory load required for the onset of metabolic reflexes,^{10, 11} which can increase peripheral muscle blood flow and oxygenation during exercise in patients with heart failure,¹⁰ thus potentially delaying the onset of fatigue, which may also contribute to the improvement in exercise capacity and subjective symptoms in this patient. Although the guidelines suggest cardiac rehabilitation in patients with pulmonary arterial hypertension, including a variety of rehabilitation modalities, it is not possible to carry out a wide range of rehabilitation therapies in the clinical reality of dealing with critically ill patients. Therefore, it is particularly important to choose the appropriate rehabilitation introduction technique to provide a starting point for a more comprehensive rehabilitation treatment and to suggest confidence in the patient's recovery. We are in the process of relevant research to clarify exactly which rehabilitation treatment can be used as this initial rehabilitation treatment. This patient's results are in line with our research expectations, and respiratory muscle rehabilitation may be an option as an introduction therapy.

Low oxygen saturation is an important cause of patients' quality of life, which is also an important indicator of the impact of disease risk stratification. This type of respiratory muscle rehabilitation, which can be implemented under home conditions, can help patients to improve their oxygen saturation even when their respiratory muscle strength is not elevated, with the aim of improving their quality of life and reducing the risk stratification of the disease.

Xinxin Yan and Ya Song reviewed the literature and wrote the manuscript; Xinxin Yan and Ya Song supervised and revised the manuscript. All authors read and approved the final manuscript.

The authors declare no conflict of interest.

Approved by the Institutional Review Board and Ethics Committee of FuWai Hospital (Approval No. 2022-1686, Approval Date: 2022-3-8), and informed consent have been properly documented.