A Retrospective Observational Study of Pulmonary Impairments in Long COVID Patients

Abstract

Background/Objective: Pulmonary impairments have been identified as some of the most complex and debilitating post-acute sequelae of SARS-CoV-2 infection (PASC) or long COVID. This study identified and characterised the specific forms of pulmonary impairments detected using pulmonary function tests (PFT), chest X-rays (CXR), and computed tomography (CT) scans in patients with long COVID symptoms. Methods: We conducted a single-centre retrospective study to evaluate 60 patients with long COVID who underwent PFT, CXR, and CT scans. Pulmonary function in long COVID patients was assessed using defined thresholds for key test parameters, enabling categorisation into normal, restrictive, obstructive, and mixed lung-function patterns. We applied exact binomial (Clopper-Pearson) 95% confidence intervals to calculate the proportions of patients falling below the defined thresholds. We also assessed the relationships among spirometric indices, lung volumes, and diffusion capacity (DLCO) using scatter plots and corresponding linear regressions. The findings from the CXRs and CT scans were categorised, and their prevalence was calculated. Results: A total of 60 patients with long COVID symptoms (mean age 60 ± 13 years; 57% female) were evaluated. The cohort was ethnically diverse and predominantly non-smokers, with a mean BMI of 32.4 ± 6.3 kg/m². PFT revealed that most patients had preserved spirometry, with mean Forced Expiratory Volume in 1 Second (FEV1) and Forced Vital Capacity (FVC) above 90% predicted. However, a significant proportion exhibited reductions in lung volumes, with total lung capacity (TLC) decreasing in 35%, and diffusion capacity (DLCO/TLCO) decreasing in 75%. Lung function pattern analysis showed 88% of patients had normal function, while 12% displayed a restrictive pattern; no obstructive or mixed patterns were observed. Radiographic assessment revealed that 58% of chest X-rays were normal, whereas CT scans showed ground-glass opacities (GGO) in 65% of patients and fibrotic changes in 55%, along with findings such as atelectasis, air trapping, and bronchial wall thickening. Conclusions: Spirometry alone is insufficient to detect impairment of gas exchange or underlying histopathological changes in patients with long COVID. Our findings show that, despite normal spirometry results, many patients exhibit significant diffusion impairment, fibrotic alterations, and ground-glass opacities, indicating persistent lung and microvascular damage. These results underscore the importance of comprehensive assessment using multiple diagnostic tools to identify and manage chronic pulmonary dysfunction in long COVID.

Keywords: alveolar gas exchange; chest CT scan; diffusion impairment; ground-glass opacities; long COVID; pulmonary function; restrictive pattern.

Figure 1

Proportion of patients with normal and restrictive lung-function patterns (N = 60). Percentages are shown with exact (Clopper–Pearson) 95% confidence intervals.

Figure 2

(a) spirometric flow diagram showing a relationship between PEF and FVC; (b) spirogram flow curves illustrate the relationship between FEV1 and FVC; (c) the relationship between FVC and TLC; (d) the relationship between RV and TLC; (e) the relationship between RV/TLC ratio and TLC. The black dots represent individual patient data points. The green line represents the linear regression line of best fit, demonstrating the correlation between the variables in each panel.

Figure 3

Chest X-ray of Long COVID Patients showing pulmonary abnormalities. Percentages denote the proportion of patients with each chest imaging finding. Clear lung fields indicate no radiological abnormalities. Opacities/infiltrates represent areas of increased attenuation consistent with inflammatory changes. Atelectasis indicates partial or complete lung collapse, while fibrotic changes reflect imaging features suggestive of pulmonary fibrosis. Images are schematic and not to scale.

Figure 4

Chest CT Scan Findings in Long COVID Patients. GGOs were seen in most CT scans: 30% widespread, 20% localised, 15% residual. Fibrosis occurred in 55% of cases: interstitial (25%), localised (17.5%), and diffuse (12.5%).