Lung-function trajectories in COVID-19 survivors after discharge: A two-year longitudinal cohort study

Abstract

Background: Data on the long-term trajectories of lung function are scarce in COVID-19 survivors.

Methods: We re-analyzed the data from a prospective longitudinal cohort follow-up study of COVID-19 survivors over 2 years after infection. All participants were divided into scale 3, scale 4 and scale 5-6 groups according to seven-category ordinal scale. The changes of pulmonary function tests (PFTs), the Modified Medical Research Council (mMRC) Dyspnea Scale, 6-min walking test health-related quality of life (HRQoL) across the three serial follow-up visits were evaluated, and compared among three groups. We performed liner regression to determine potential factors that were associated with changes of PFTs and distance walked in 6 minutes (6MWD).

Findings: In this study, 288 participants generally presented an improvement of PFTs parameters from 6 months to 1 year after infection. The scale 5-6 group displayed a significantly higher increase of PFTs compared with scale 3 and scale 4 groups (all p<0.0167), and corticosteroids therapy was identified as a protective factor for the PFTs improvement with a correlation coefficient of 2.730 (0.215-5.246) for forced vital capacity (FVC), 2.909 (0.383-5.436) for total lung capacity (TLC), and 3.299 (0.211-6.387) for diffusion capacity for carbon monoxide (DLco), respectively. From 1-year to 2-year follow-up, the PFTs parameters generally decreased, which was not observed to be associated with changes of 6MWD and HRQoL. Dyspnea (mMRC≥1) generally decreased over time (23.3% [61/262] for 6-month, 27.9% [67/240] for 1-year, 13.4% [35/261] for 2-year), and 6MWD increased continuously (500.0 m vs 505.0 m vs 525.0 m).

Interpretation: Corticosteroids therapy during hospitalization was a protective factor for PFTs improvement from 6 months to 1 year. The relatively fast decline trend of PFTs from 1 year to 2 years needs to be paid attention and further validated in the future follow-up study.

Fundings: This work was supported by Chinese Academy of Medical Sciences Innovation Fund for Medical Sciences (CIFMS 2021-I2M-1-048) and the National Key Research and Development Program of China (2021YFC0864700).

Keywords: COVID-19; Corticosteroids; Long COVID; Lung function; Pulmonary function tests.

Figure 1

The temporal changes in PFTs, dyspnea and 6MWD by severity scales. Note. The temporal changes of the percentage of predicted for FVC (A), TLC (B) and DLco (C) at 6-month, 1-year and 2-year follow-up. Data are mean and error. PFTs=pulmonary function tests. FVC=forced vital capacity. TLC=total lung capacity. DLco=diffusion capacity for carbon monoxide. The temporal changes of the proportion of dyspnea (D) and the median of 6MWD (E). Dyspnea was defined as mMRC≥1. Scale 3: not requiring supplemental oxygen. Scale 4: requiring supplemental oxygen. Scale 5–6: requiring high-flow nasal cannula, non-invasive mechanical ventilation, or invasive mechanical ventilation. *p<0.05.

Figure 2

Post-COVID lung-function trajectories over 2 years after infection. Note. The two trajectories (red-line below: critical; green-line above: moderate-severe) present the Post-COVID lung-function patterns. Moderate-severe with smaller improvement than critical patients from T₁ to T₂ and reach the peak earlier. Period from T₁ to T₂ dominated by an increase in FVC was defined as lung function recovery, and duration between T₂ and T₃ dominated by a decrease in TLC and DLco was defined as lung function decline. The changes in lung function recovery period were significant differed between two trajectories, but no statistics difference been observed in lung function decline period between them. The dotted lines from T₀ to T₁ refer to previous studies (PMID: 32554533, 32381497 and 35018338), and the dotted lines after T₃ refer to the decline rate between T₂ and T₃. FVC=forced vital capacity. TLC=total lung capacity. DLco=diffusion capacity for carbon monoxide.(For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)