Post-discharge chest CT findings and pulmonary function tests in severe COVID-19 patients

Abstract

Purpose: To evaluate chest computed tomography (CT) and pulmonary function test (PFT) findings in severe COVID-19 patients after discharge and correlate CT pulmonary involvement with PFT results.

Methods: COVID-19 patients admitted to our hospital between February 25 and May 2, 2020, were retrospectively included according to the following criteria: (a) COVID-19 defined as severe based on the WHO interim guidance (i.e., clinical signs of pneumonia plus respiratory rate > 30 breaths/min, severe respiratory distress, and/or SpO₂ < 90 % on room air); (b) chest radiograph in the acute setting; (c) post-discharge unenhanced chest CT; and (d) post-discharge comprehensive PFT. Imaging findings were retrospectively evaluated in consensus by two readers, and volume of abnormal lung was measured on CT using 3D Slicer software. Differences between demographics, comorbidities, acute radiographic findings, PFT, and post-discharge clinical and laboratory data of patients with normal and abnormal CT findings were assessed by Mann-Whitney or Fisher tests, and the compromised lung volume-PFT association by Pearson correlation after removing possible outliers.

Results: At a median of 105 days from symptom onset, 74/91 (81 %) patients had CT abnormalities. The most common CT pattern was combined ground-glass opacity and reticular pattern (46/74, 62 %) along with architectural distortion (68/74, 92 %) and bronchial dilatation (66/74, 89 %). Compromised lung volume had a median value of 15 % [11-23], was higher in dyspneic patients, and negatively correlated with the percentage of predicted DLCO, VA, and FVC values (r = -0.39, -0.5, and -0.42, respectively). These PFT parameters were significantly lower in patients with CT abnormalities. Impairment of DLCO and KCO was found in 12 (13 %) cases, possibly implying an underlying pulmonary vasculopathy in this subgroup of patients.

Conclusions: Most severe COVID-19 survivors still had physiologically relevant CT abnormalities about three months after the disease onset, with an impairment of diffusion capacity on PFT. A pulmonary vasculopathy was suggested in a minor proportion of patients.

Keywords: COVID-19; Lung diseases; Respiratory function tests; Severe acute respiratory syndrome coronavirus 2; Survivors; Tomography.

Fig. 1

Participant flow diagram.

Fig. 2

Lung abnormality quantification on chest CT in a 61-year-old man who suffered severe COVID-19. (A) Unenhanced chest CT scan acquired 85 days after the disease onset shows residual bilateral lung abnormalities (white arrowheads). (B) The semiautomated segmentation performed by 3D Slicer software highlights the residual lung abnormalities (yellow) and normally aerated lung (blue). (C) 3D volumetric representation of both lungs illustrates the distribution of parenchymal abnormalities (yellow) and normally aerated lung (blue). The percentage of compromised lung volume was quantified as 20.7 %.

Fig. 3

Images from unenhanced chest CT scan of an 89-year-old man who suffered severe COVID-19. The examination was performed 96 days after the disease onset. Axial images show bilateral ground-glass opacity with superimposed reticulation (white arrowheads, A and B), parenchymal bands (black arrowheads, A) and subpleural curvilinear opacities (gray arrowhead, B).

Fig. 4

Unenhanced chest CT scan of a 58-year-old man who suffered severe COVID-19. The examination was performed 88 days after the disease onset. Axial image shows pure faint ground-glass opacity in the right upper and lower lobes (white arrowheads).

Fig. 5

Unenhanced chest CT scan of an 82-year-old man who suffered severe COVID-19. The examination was performed 98 days after the disease onset. Axial image shows central bronchial dilatations (white arrowheads) and scissural distortion (empty arrowhead). Reticulation coexisted in both lungs.

Fig. 6

Associations between pulmonary involvement on CT and dyspnea intensity and pulmonary function test findings in 74 COVID-19 survivors. (A) Distribution of compromised lung volume on CT by the mMRC dyspnea score: p values denote significance in overall and pairwise differences assessed by Kruskal-Wallis and Wilcoxon test, respectively. (B-D) Linear regression of compromised lung volume on DLCO, FVC, and VA % predicted. R denotes Pearson's correlation coefficient, with the pertinent p-value. Abbreviations: mMRC = modified Medical Research Council, DLCO = diffusion capacity for carbon monoxide, FVC = forced vital capacity, VA = alveolar volume.

Fig. 7

Unenhanced chest CT scan of a 59-year-old man who suffered severe COVID-19. The examination was performed 84 days after the disease onset. Axial image shows lower lobe predominant ground-glass opacity admixed with reticulation (white arrowheads) and relative sparing of the subpleural lung, suggesting a non-specific interstitial pneumonia pattern.