Respiratory muscle training with an app-based device improves persistent shortness of breath in patients after SARS-CoV-2 Infection – a randomized controlled trial

Background: Post-acute sequelae of SARS-CoV-2 infection (PASC) is defined as persistent or newly experienced symptoms after the disease. Shortness of breath is a common symptom reported by individuals with PASC. Respiratory muscle training (RMT) to strengthen respiratory muscles (e.g diaphragm, intercostal muscles) can improve symptoms in various diseases. The aim of the study therefore was to investigate the effectiveness of RMT for the reduction of PASC-related shortness of breath by a daily home-based app-guided training intervention. Methods: Sixteen patients (age 32.0±16.1 years (Mean±SD), female N=9) suffering from persistent shortness of breath after SARS-CoV-2 infection were randomized to either an Intervention-first-group (IfG) starting with RMT immediately or an Intervention-second-group (IsG) receiving RMT after a control period of one month. RMT was conducted using a commercially available training device and daily app-based RMT instructions. Severity of respiratory symptoms was measured using the St. Georges Respiratory questionnaire (SGRQ). Ventilation parameters and peak oxygen consumption (V˙ O2peak) were assessed by cardio pulmonary exercise testing (CPET). Results: Fifteen patients completed the study. The RMT intervention led to a significant improvement of subjective symptoms (SGRQ reduction: -11.41±8.28, p<0.001, d=-1.38, 95% CI [-0.65, -2.08], Subjective health: 12.43±11.51%, p=0.001, d=1.08, 95% CI [0.40, 1.73]) and improved maximum ventilation (8.94±9.23 l/min, p=0.003, d=0.97, 95% CI [0.31, 1.59]). Exercise capacity and V˙ O2peak significantly increased in a subgroup of patients with low VO2peak values at study inclusion (relPmax: 0.24±0.26 W/kg, p=0.022, d=0.95, 95% CI [1.13, 1.72]), relVO2peak: 2.98±5.79 ml/min*kg, p=0.013, d=1.10 95% CI 0.21,1.89]). During the control period (only IsG) symptoms, maximum power output and VO2peak remained unchanged with only maximum ventilation significantly decreasing. Conclusions: Patients with persistent shortness of breath after SARS-CoV-2 infection benefit from intense, regular RMT over one month. Patients reported an increase in overall health status and an improvement in V˙O2peak and exercise capacity was reached in those with low VO2peak values at the beginning.