, according to a prospective study that compared 100 COVID-19 survivors who had persistent symptoms and 106 healthy control persons.
“Something is going on in the distal airways related to either inflammation or fibrosis that is giving us a signal of air trapping,” noted senior author Alejandro P. Comellas, MD, in a press release. The study was stimulated by reports from University of Iowa clinicians noting that many patients with initial SARS-CoV-2 infection who were either hospitalized or were treated in the ambulatory setting later reported shortness of breath and other respiratory symptoms indicative of chronic lung disease.
Investigators classified patients (mean age, 48 years; 66 women) with post-acute sequelae of COVID-19 according to whether they were ambulatory (67%), hospitalized (17%), or required treatment in the intensive care unit (16%). They then compared CT findings of patients who had COVID-19 and persistent symptoms with those of a healthy control group.
COVID-19 severity did not affect the percentage of cases of lung with air trapping among these patients. Air trapping occurred at rates of 25.4% among ambulatory patients, 34.6% in hospitalized patients, and in 27.3% of those requiring intensive care (P = .10). The percentage of lungs affected by air trapping in ambulatory participants was sharply and significantly higher than in healthy controls (25.4% vs. 7.2%; P < .001). Also, air trapping persisted; it was still present in 8 of 9 participants who underwent imaging more than 200 days post diagnosis.
Qualitative analysis of chest CT images showed that the most common imaging abnormality was air trapping (58%); ground glass opacities (GGOs) were found in 51% (46/91), note Dr. Comellas and coauthors. This suggests ongoing lung inflammation, edema, or fibrosis. These symptoms are often observed during acute COVID-19, frequently in an organizing pneumonia pattern, and have been shown to persist for months after infection in survivors of severe disease. The mean percentage of total lung classified as having regional GGOs on chest CT scans was 13.2% and 28.7%, respectively, in the hospitalized and ICU groups, both very much higher than in the ambulatory group, at 3.7% (P < .001 for both). Among healthy controls, the GGO rate on chest CT was only 0.06% (P < .001).
In addition, air trapping correlated with the ratio of residual volume to total lung capacity (r = 0.6; P < .001) but not with spirometry results. In fact, the investigators did not observe airflow obstruction by spirometry in any group, suggesting that air trapping in these patients involves only small rather than large airways and that these small airways contribute little to total airway resistance. Only when a large percentage, perhaps 75% or more, of all small airways are obstructed will spirometry pick up small airways disease, the authors observe.
The findings taken together suggest that functional small airways disease and air trapping are a consequence of SARS-CoV-2 infection, according to Dr. Comellas. “If a portion of patients continues to have small airways disease, then we need to think about the mechanisms behind it,” he said. “It could be something related to inflammation that’s reversible, or it may be something related to a scar that is irreversible, and then we need to look at ways to prevent further progression of the disease.” Furthermore, “studies aimed at determining the natural history of functional small airways disease in patients with post-acute sequelae of COVID-19 and the biological mechanisms that underlie these findings are urgently needed to identify therapeutic and preventative interventions,” Dr. Comellas, professor of internal medicine at Carver College of Medicine, University of Iowa, Iowa City, concluded.