The RETORNUS Study: Dual Training to Restore the Function of Respiratory Muscles in Stroke Patients

Stroke is a major cause of morbidity and mortality worldwide. It determines a substantial socioeconomic burden. Stroke can lead to varying degrees of oropharyngeal dysphagia (25-85% of patients) and respiratory muscle dysfunction associated with an increase in medical complications such as bronchoaspiration pneumonia, malnutrition and death. The respiratory muscle dysfunction is a common functional abnormality in chronic respiratory diseases such as chronic obstructive pulmonary disease (COPD), heart failure, multiple sclerosis in which it has been shown to modify the expected survival. Dysphagia is present in a significant proportion of patients admitted to Rehabilitation (up to 85% depending on series) in the subacute phase of stroke. There is no drug able to restore the swallowing function and inspiratory and expiratory muscle function in these patients. Consequently, neurological rehabilitation is the mainstay of treatment of these disorders.

Amino acids (AA) are essential for proper protein synthesis. Skeletal muscle represents the largest reserve of body AA, which may be used according to metabolic needs. Within this group of compounds, the most involved in muscle metabolism are glutamate, aspartate, asparagine, valine, leucine and isoleucine. A pathobiological association between decrease in muscle glutamate and diaphragm dysfunction in patients with chronic respiratory diseases has been demonstrated in chronic respiratory patients. Moreover, glutamate levels of the diaphragm can be restored as a result of muscle training, playing a decisive role as a precursor of certain AA (glutamine and alanine), and glutathione in patients with COPD. Other studies have defined that glutamine may be a biomarker of training response in healthy individuals. Several publications have reflected the decrease of glutamine and glutamate as a result of different diseases and in some cases have tried to supplement this deficit.

Muscle dysfunction is defined as a function impairment (decrease in strength and/or resistance) of muscles whose main consequence is muscle fatigue. Although exercise training has been used successfully to restore function in patients with some chronic illnesses and frailty, there is little evidence of the beneficial effects of an overall muscle training in stroke patients. Regarding peripheral muscles, a high-intensity training improves strength and endurance of lower limbs muscles (paretic and non paretic) in stroke patients. Dysfunction of the diaphragm and other respiratory muscles has important clinical implications. It associates with susceptibility to hypercapnic ventilatory failure, ineffective cough, and even higher incidence of repeated hospital admissions and mortality. Therefore, respiratory muscle weakness described in some stroke patients justifies the need to train respiratory muscles because there is no general exercise (bicycle, legs, arms) able to induce an overload enough to achieve training effect on respiratory muscles.