Abstract
PURPOSE: Symptoms often persistent for more than 4 weeks after COVID-19-now commonly referred to as 'Long COVID'. Independent of initial disease severity or pathological pulmonary functions tests, fatigue, exertional intolerance and dyspnea are among the most common COVID-19 sequelae. We hypothesized that respiratory muscle dysfunction might be prevalent in persistently symptomatic patients after COVID-19 with self-reported exercise intolerance. METHODS: In a small cross-sectional pilot study (n = 67) of mild-to-moderate (nonhospitalized) and moderate-to-critical convalescent (formerly hospitalized) patients presenting to our outpatient clinic approx. 5 months after acute infection, we measured neuroventilatory activity P(0.1), inspiratory muscle strength (PI(max)) and total respiratory muscle strain (P(0.1)/PI(max)) in addition to standard pulmonary functions tests, capillary blood gas analysis, 6 min walking tests and functional questionnaires. RESULTS: Pathological P(0.1)/PI(max) was found in 88% of symptomatic patients. Mean PI(max) was reduced in hospitalized patients, but reduced PI(max) was also found in 65% of nonhospitalized patients. Mean P(0.1) was pathologically increased in both groups. Increased P(0.1) was associated with exercise-induced deoxygenation, impaired exercise tolerance, decreased activity and productivity and worse Post-COVID-19 functional status scale. Pathological changes in P(0.1), PI(max) or P(0.1)/PI(max) were not associated with pre-existing conditions. CONCLUSIONS: Our findings point towards respiratory muscle dysfunction as a novel aspect of COVID-19 sequelae. Thus, we strongly advocate for systematic respiratory muscle testing during the diagnostic workup of persistently symptomatic, convalescent COVID-19 patients.