Severity of respiratory failure and computed chest tomography in acute COVID-19 correlates with pulmonary function and respiratory symptoms after infection with SARS-CoV-2: An observational longitudinal study over 12 months

Abstract

Introduction: Prospective and longitudinal data on pulmonary injury over one year after acute coronavirus disease 2019 (COVID-19) are sparse. We aim to determine reductions in pulmonary function and respiratory related quality of life up to 12 months after acute COVID-19.

Methods: Patients with acute COVID-19 were enrolled into an ongoing single-centre, prospective observational study and prospectively examined 6 weeks, 3, 6 and 12 months after onset of COVID-19 symptoms. Chest CT-scans, pulmonary function and symptoms assessed by St. Georges Respiratory Questionnaire were used to evaluate respiratory limitations. Patients were stratified according to severity of acute COVID-19.

Results: Median age of all patients was 57 years, 37.8% were female. Higher age, male sex and higher BMI were associated with acute-COVID-19 severity (p < 0.0001, 0.001 and 0.004 respectively). Also, pulmonary restriction and reduced carbon monoxide diffusion capacity was associated with disease severity. In patients with restriction and impaired diffusion capacity, FVC improved over 12 months from 61.32 to 71.82, TLC from 68.92 to 76.95, D_LCO from 60.18 to 68.98 and K_CO from 81.28 to 87.80 (percent predicted values; p = 0.002, 0.045, 0.0002 and 0.0005). The CT-score of lung involvement in the acute phase was associated with restriction and reduction in diffusion capacity in follow-up. Respiratory symptoms improved for patients in higher severity groups during follow-up, but not for patients with initially mild disease.

Conclusion: Severity of respiratory failure during COVID-19 correlates with the degree of pulmonary function impairment and respiratory quality of life in the year after acute infection.

Keywords: COVID-19; Long-COVID; Pneumonia; Post-COVID; Post-acute COVID; Pulmonary function; Pulmonary outcome; Pulmonary restriction; Pulmonary sequelae; Quality of life; SARS-CoV-2.

Graphical abstract

Fig. 1

Pulmonary restriction increased with disease severity. Bodyplethysmography 6 weeks, 3, 6 and 12 months post SARS-CoV-2 infection showed marked differences for FVC and TLV for all time points. Diffusion capacity is reduced in the early reconvalescent phase post COVID-19. DLCO strongly correlates with disease severity in the follow-up phase for all time points, whereas this trend is less remarkably seen for KCO after acute COVID-19. (Abbreviations: ppv – percent predicted value; NOO – no oxygen outpatient; NOH – no oxygen hospitalized, LFO – low-flow oxygen; HFO – high-flow oxygen; IMV – invasive mechanical ventilation; ECMO – extracorporeal membrane oxygenation; ns = P ≥ 0.05; * = P < 0.05; ** = P < 0.01; *** = P < 0.001; **** < P ≤ 0.0001).

Fig. 2

Pulmonary restriction and impaired diffusion capacity improves over time. FVC, TLC, DLCO and KCO during follow up showed improvements in patients with initially reduced pulmonary function test results. Changes in relevant pulmonary function parameters are shown between first follow-up and month 12 follow up for every single individual, represented by a connecting line. (Abbreviations: FFU – first follow-up, M12 – month 12 follow-up).

Fig. 3

a) CT-score as suggested by Pan et al. at time of hospital admission (median 9 days post symptom onset) showed a increase in pulmonary involvement with higher disease severity determined be level of respiratory support. b) Representative CT-chest scans assessed using the 6-point scale of Pan et al. This figure shows left lower lobe involvement of 0% (score 0), <5% (score 1), 5–25% (score 2), 26–50% (score 3), 51–75% (score 4), and >75% (score 5) on axial, coronal, and sagittal CT sections.

Fig. 4

The proportion of pulmonary involvement during acute phase negatively correlates with first pulmonary function test post-acute COVID-19 for TLC, FVC and DLCO. Linear regression analysis reveals for every 10 points increase in CT-score an estimated decrease of 15 %-points TLC and 10 %-points FVC and DLCO post-acute COVID-19.

Fig. 5

Symptom load and patient reported health outcome 6 weeks, 3, 6, and 12 months post-acute COVID: a) Cumulative median SGRQ-Score develops divergently over 12 months for different disease severity groups. Median total SGRQ is higher after HFO, IMV and ECMO treatment initially and decreases until month 12, whereas for LFO, NOH and NOO it remains constant over time of follow-up over 12 months. b) Cumulative symptom load for most frequently reported symptoms (as %) during follow up. Fatigue and respiratory symptoms score highest during follow up over 12 months. The proportion of patients reporting fatigue, pulmonary- and neurocognitive sequelae in our cohort remains high 12 months post-acute COVID-19.