The etiology of long COVID/Post-COVID Condition (PCC) remains an enigma. Recent studies consider multiple causes which remain under investigation. Additional questions remain whether invasive ventilation increases the incidence or severity of symptoms. Many COVID-19 survivors report dyspnea that cannot be explained by routine clinical diagnostic measures, including pulmonary function tests and cardiac evaluation. This study investigated 50 patients previously hospitalized with COVID-19 (14 female, age 58±12 years), half were treated with mechanical ventilation and the remaining outpatients using pulmonary function testing, 6-minute walk test, echocardiography, twitch transdiaphragmatic pressure following cervical magnetic stimulation of the phrenic nerve roots, and diaphragm ultrasound. Diaphragm function data were compared with values from a healthy control group. Testing evaluated both voluntary and involuntary (magnetic phrenic nerve stimulation) measurements of inspiratory and expiratory power at FRC. Dyspnea was equally experienced between survivors who required invasive ventilation (including ECMO) and those managed without. Diaphragmatic inspiratory strength reflected in voluntary and magnetically induced twitch pressures generated at functional residual capacity (FRC) and diaphragmatic thickening noted on ultrasound were reduced. Expiratory values similarly measured showed minimal disruption of expiration. The study demonstrated diaphragm muscle weakness underlying otherwise unexplained exertional dyspnea in patients previously hospitalized for COVID-19 and suggested specific interventions, such as inspiratory muscle training, could be an effective approach to mitigate COVID-19 exertional dyspnea.

https://www.atsjournals.org/doi/pdf/10.1164/rccm.202206-1243OC