Reduced Diffusion Capacity in COVID-19 Survivors

Clinicians and researchers are increasingly recognizing lasting sequelae of coronavirus disease 2019 (COVID-19) among survivors of the disease. Among a wide range of symptoms reported by patients in the months after COVID-19, shortness of breath is common and persistent in many. Therefore, it is essential to understand the trajectory of pulmonary function after COVID-19. This will allow further study of mechanisms of lung injury, therapeutic approaches, and prognostication for patients experiencing post-COVID impairment in pulmonary function. To date, several studies have reported the results of pulmonary function tests performed early in the course of COVID-19 pneumonia, including prior to hospital discharge or in the early post–acute care period up to 3 months after discharge.^{1, 2}

Given this context, Méndez and colleagues sought to describe the pulmonary function of patients in the months following hospitalization for COVID-19. They recruited 239 consecutive patients from a single hospital in Spain following acute care hospitalization—215 patients ultimately were included in the study, as they attended follow-up and completed acceptable pulmonary function tests (PFT). The median time to follow-up was approximately 3 months. At that time, full pulmonary function tests were performed. The authors report the results of these tests along with a linear regression model that sought to estimate the association between patient factors (demographics, severity of illness, lab values) and the diffusing capacity for carbon monoxide (DLCO) measurement.

The authors report that (DLCO) measurement was reduced to less than 80% predicted among 24.7% of patients at the time of their follow-up. In multivariable linear regression, female sex, smoking history, intensive care unit (ICU) admission, and greater peak D-dimer value were all most strongly associated with reduced DLCO. Only 4.7% and 8.8% of patients had FVC and FEV₁ reduced to less than 80% predicted, respectively.

This study provides further evidence of altered pulmonary function following COVID-19 pneumonia. Importantly, one must then ask: how unique is this finding to COVID-19? Is this change expected in the months following any pneumonia severe enough to require hospitalization, cause hypoxemia, and warrant ICU admission in many patients? In fact, data prior to the COVID-19 pandemic, from populations ranging from those with mild H1N1 influenza to acute respiratory distress syndrome, commonly describe diffusion impairments in the months to years after illness.^{3, 4} Therefore, these impairments do not appear to be unique to COVID-19 in the early post-acute illness period, although the long-term trajectory of patients remains to be seen. Future studies should obtain repeated longitudinal data from patients during the course of recovery to better understand the trajectory of lung function. It will also be important to incorporate patient-centered measures, such as measures of breathlessness and quality of life. This will allow us to better understand what impact these impairments in pulmonary function have on the lives of patients, and if the dyspnea that is increasingly described by patients after COVID-19 is associated with these measurable impairments.

References

1. Mo X, Jian W, Su Z, et al. Abnormal pulmonary function in COVID-19 patients at time of hospital discharge. Eur Respir J. 2020;55(6):2001217. https://erj.ersjournals.com/content/55/6/2001217.long
2. Frija-Masson J, Debray MP, Gilbert M, et al. Functional characteristics of patients with SARS-CoV-2 pneumonia at 30 days post-infection. Eur Respir J. 2020;56(2):2001754. https://erj.ersjournals.com/content/56/2/2001754.long
3. Herridge MS, Tansey CM, Matté A, et al. Functional disability 5 years after acute respiratory distress syndrome. N Engl J Med. 2011;364(14):1293-1304. https://www.nejm.org/doi/full/10.1056/nejmoa1011802
4. Liu W, Peng L, Liu H, Hua S. Pulmonary function and clinical manifestations of patients infected with mild influenza A virus subtype H1N1: a one-year follow-up. PLoS One. 2015;10(7):e0133698. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0133698