Investigation of changes in lung function test parameters following coronavirus disease (COVID-19) infection and associated factors

<p>The novel coronavirus infection (COVID-19: coronavirus disease 2019), which has caused a global pandemic since 2019, has been reported to have a significant impact on the respiratory system, particularly resulting in restricted ventilation impairment and decreased pulmonary diffusion capacity. However, there are no reports on lung function tests (LFTs) in Japan. In this study, we investigated changes in LFT results over time and normal factors after COVID-19 infection. LFTs were performed at 3, 6, and 9–12 months in 50 patients (33 in the normal group: forced vital capacity % predicted (%FVC) ≥ 80% and diffusing capacity of the lung for carbon monoxide % predicted (%DL_CO) ≥ 80% and 17 in the decreased group: %FVC < 80% or %DL_CO <80%) after discharge from the hospital. The results showed that the decreased group had higher severity, longer hospital stays, and more residual symptoms. Although the total lung capacity (TLC) was improved in the decreased group 9–12 months after treatment, the measured %TLC was lower than that in the normal group, indicating potential residual fibrosis or inflammation, which was caused by interstitial pneumonia. The factor most strongly associated with the decreased group was %DL_CO, but its longitudinal changes were limited. Diffusion impairment was speculated to persist for a long time and could be observed at 3 months after discharge, indicating its involvement in long-term lung dysfunction. The decreased group in this study demonstrated restrictive ventilation impairment and decreased lung diffusion capacity, indicative of long-term lung dysfunction. Furthermore, %DL_CO at 3 months after discharge was identified as a factor associated with normal or decreased LFT parameters following COVID-19 infection.</p>