Impairment of Inspiratory Muscle Function after COVID-19

Background: Persistent symptoms after acute coronavirus-disease-2019 (COVID-19) are common, and there is no significant correlation with the severity of the acute disease. In long-COVID (persistent symptoms >4 weeks after acute COVID-19), respiratory symptoms are frequent, but lung function testing shows only mild changes that do not explain the symptoms. Although COVID-19 may lead to an impairment of the peripheral nervous system and skeletal muscles, respiratory muscle function has not been examined in this setting. Methods: In this study, we assessed the severity of dyspnea (NYHA-function class) in long-COVID patients and analyzed its association with body mass index (BMI), FEV1, forced vital capacity, other parameters of body plethysmography, diffusing capacity for carbon monoxide (DLCO), arterial blood gases, and inspiratory muscle function, assessed by airway occlusion pressure (P0.1) and maximal inspiratory pressure (PImax) in two respiratory clinics in Germany between Oct 2020 and Aug 2021. Results: A total of 116 patients were included in the study. The mean age was 50.2 ± 14.5 years; BMI, 26.7 ± 5.87 kg/m2; NYHA class I, 19%; II, 27%; III, 41%; and IV, 14%. While lung function values and computed tomography or conventional X-ray of the chest were in the normal range, inspiratory muscle function was markedly impaired. P01 was elevated to 154 ± 83%predicted and PImax was reduced to 41 ± 25%predicted. PImax reduction was strongly associated with the severity of dyspnea but independent of BMI, time after acute COVID-19 and most of the other parameters. Conclusions: This study shows that in long-COVID patients, respiratory symptoms may be mainly caused by reduced inspiratory muscle strength. Assessment of PImax and P0.1 might better explain dyspnea than classical lung function tests and DLCO. A prospective study is needed to confirm these results.