Persistence of Diffusion Capacity Impairment and Its Relationship with Dyspnea 12 Months after Hospitalization for COVID-19.

Background: Dyspnea is a common persistent symptom after acute coronavirus disease 2019 illness (COVID-19). One potential explanation for post-COVID-19 dyspnea is a reduction in diffusion capacity. This longitudinal study investigated diffusion capacity and its relationship with dyspnea on exertion in individuals previously hospitalized with COVID-19. Methods: Eligible participants had been hospitalized for the treatment of acute COVID-19 and were assessed at 6 weeks, 6 months, and 12 months after discharge. Pulmonary function testing, diffusion capacity of carbon monoxide (DLCO), blood gas analysis and the level of dyspnea (Borg scale; before and after a 6 min walk test [6 MWT]) were performed. Participants were divided into subgroups based on the presence or absence of dyspnea during the 6 MWT at 12 months after hospitalization. Results: Seventy-two participants (twenty-two female, mean age 59.8 ± 13.5 years) were included. At 12 months after discharge, 41/72 participants (57%) had DLCO below the lower limit of normal and 56/72 (78%) had DLCO < 80% of the predicted value. Individuals with exertional dyspnea had significantly lower DLCO than those without exertional dyspnea (p = 0.001). In participants with DLCO data being available at three timepoints over 12 months (baseline, 6 months, and 12 months) after discharge (n = 25), DLCO improved between 6 weeks and 6 months after hospital discharge, but not thereafter (p = 0.017). Conclusions: About 2/3 of the post-COVID individuals in this study had impaired diffusion capacity at 12 months after hospital discharge. There was an association between persisting dyspnea on exertion and significantly reduced DLCO. Impaired diffusion capacity improved over the first 6 months after hospitalization but not thereafter.

GLI-12 Reference Values versus Fixed 0.7 Ratio for the Detection of Airflow Obstruction in the Presence of Lung Hyperinflation.

Introduction: Airflow obstruction (AO) is evidenced by reduced forced expiratory volume in 1 s/forced vital capacity (FEV1/FVC) with the threshold for diagnosis often being set at <0.7. However, currently the ATS/ERS standards for interpretation of lung function tests recommend the lower limit of normal (LLN), calculated by reference equations of the Global Lung Initiative from 2012 (GLI-12), as a threshold for AO diagnosis. The present study aims to investigate phenotypes, with focus on hyperinflation, which influence AO prevalence defined by FEV1/FVC < LLN when compared to the fixed 0.7 threshold. Methods: Data from 3,875 lung function tests (56.4% men, aged 18-95) including 3,824 body plethysmography recordings performed from July 2021 to June 2022 were analysed. The difference between both classifiers was quantified, before and after stratification by sex, age, and hyperinflation. Results: AO diagnosis was significantly less frequent with the LLN threshold (18.2%) compared to the fixed threshold (28.0%) (p < 0.001) with discordance rate of 10.5%. In the presence of mild or moderate hyperinflation, there was substantial agreement (Cohen's kappa: 0.616, 0.718) between the classifiers compared to near perfect agreement in the presence of severe hyperinflation (Cohen's kappa: 0.896). In addition, subgroup analysis after stratification for sex, age, and hyperinflation showed significant differences between both classifiers. Conclusion: The importance of using the LLN threshold instead of the fixed 0.7 threshold for the diagnosis of AO is highlighted. When using the fixed threshold AO, misdiagnosis was more common in the presence of mild to moderate hyperinflation.