Rationale Dyspnea is often a persistent symptom after acute coronavirus disease (COVID-19), even if cardiac and pulmonary function are normal. Objectives This study investigated diaphragm muscle strength in patients after COVID-19 and its relationship to unexplained dyspnea on exertion. Methods Fifty patients previously hospitalized with COVID-19 (14 female, age 58 ± 12 yr, half of whom were treated with mechanical ventilation, and half of whom were treated outside the ICU) were evaluated using pulmonary function testing, 6-minute-walk test, echocardiography, twitch transdiaphragmatic pressure after cervical magnetic stimulation of the phrenic nerve roots, and diaphragm ultrasound. Diaphragm function data were compared with values from a healthy control group. Measurements and Main Results Moderate or severe dyspnea on exertion was present at 15 months after hospital discharge in approximately two-thirds of patients. No significant pulmonary function or echocardiography abnormalities were detected. Twitch transdiaphragmatic pressure was significantly impaired in patients previously hospitalized with COVID-19 compared with control subjects, independent of initial disease severity (14 ± 8 vs. 21 ± 3 cm H 2 O in mechanically ventilated patients vs. control subjects [ P = 0.02], and 15 ± 8 vs. 21 ± 3 cm H 2 O in nonventilated patients vs. control subjects [ P = 0.04]). There was a significant association between twitch transdiaphragmatic pressure and the severity of dyspnea on exertion ( P = 0.03). Conclusions Diaphragm muscle weakness was present 15 months after hospitalization for COVID-19 even in patients who did not require mechanical ventilation, and this weakness was associated with dyspnea on exertion. The current study, therefore, identifies diaphragm muscle weakness as a correlate for persistent dyspnea in patients after COVID-19 in whom lung and cardiac function are normal. Clinical trial registered with www.clinicaltrials.gov (NCT 04854863).

Some COVID-19 patients experience dyspnea without objective impairment of pulmonary or cardiac function. This study determined diaphragm function and its central voluntary activation as a potential correlate with exertional dyspnea after COVID-19 acute respiratory distress syndrome (ARDS) in ten patients and matched controls. One year post discharge, both pulmonary function tests and echocardiography were normal. However, six patients with persisting dyspnea on exertion showed impaired volitional diaphragm function and control based on ultrasound, magnetic stimulation and balloon catheter-based recordings. Diaphragm dysfunction with impaired voluntary activation can be present 1 year after severe COVID-19 ARDS and may relate to exertional dyspnea.This prospective case–control study was registered under the trial registration number NCT04854863 April, 22 2021

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