Aim of investigators was to study whether abnormalities of lung diffusing capacity for nitric oxide (DLNO) and carbon monoxide (DLCO) in long COVID may have a clinical impact in relation to exercise intolerance.

Prolonged recovery from acute coronavirus disease 2019 (long COVID) is characterized in about 30% of subjects from breathlessness and fatigue also during daily activities often associated to decreased lung diffusing capacity for carbon monoxide (DLCO) at rest. Aim of investigators was to study whether abnormalities of lung diffusing capacity for nitric oxide (DLNO) and DLCO in long COVID may have a clinical impact in relation to exercise intolerance. Combined DLNO and DLCO were simultaneously measured at rest and immediately after a short bout of treadmill walking in 32 dyspneic subjects ≥3 months after the COVID-19 acute phase. A group of healthy subjects served as a control group.

Inclusion Criteria:

• History of dyspnea, fatigue, and exercise intolerance persisting or occurring at least 3 months after the COVID-19 acute phase and lasting ≥2 months.

Exclusion Criteria:

• History of diseases potentially causing dyspnea or affecting pulmonary gas transport, i.e., bronchial asthma, lung bullous disease, chronic obstructive pulmonary disease, pulmonary interstitial fibrosis or vasculitis, hematological diseases, systemic collagen diseases, congestive heart failure, liver or renal diseases, and morbid obesity.

Caucasian subjects with a history of SARS CoV-2 infection confirmed by nasopharyngeal swab with real-time polymerase-chain reaction. They were referred to our pulmonary function laboratory after being tested negative for SARS-CoV-2, because of dyspnea, fatigue, and exercise intolerance persisting or occurring at least 3 months after the COVID-19 acute phase and lasting ≥2 months.