Decreases in lung volume and lung height among ankylosing spondylitis patients with pulmonary function impairment: a 3D CT investigation.

Background: Respiratory compromise among ankylosing spondylitis (AS) patients is characterized by restrictive pulmonary function, leading to the need for a meticulous assessment of lung volume. Compared with conventional pulmonary function tests (PFTs), CT-based lung volume measurements have superior accuracy and are crucial for understanding functional limitations in AS. This study investigated the correlation between CT lung volume and PFT parameters in AS patients, with a focus on changes in CT parameters and lung volume in patients with compromised pulmonary function.

Methods: A total of 79 AS patients were included, and their full-length radiographs, thoracic CT scans, and PFT data were analysed. Specialized software was used to estimate the total and lobar lung volumes from the CT scans. The relationship between lung volume and PFT results was examined, and a multiple linear regression model was constructed to determine the influence of radiographic and CT parameters on total lung volume (TLV). Patients were classified into normal or impaired pulmonary function groups based on PFT outcomes, thus facilitating comparative analyses of radiographic and CT parameters and lung volumes between these groups.

Results: Among the 79 AS patients, 19 had normal function, 4 had mixed dysfunction, and 56 experienced restrictive dysfunction. PFT parameters, including FVC, FEV1, TLC, FEV1%, and TLC%, showed varying correlations with TLV and individual lobe volume. Patients with compromised pulmonary function exhibited more pronounced spinal kyphosis and experienced a decline in TLV. Multiple regression analysis revealed that lung height and horizontal and vertical lung diameters independently influenced TLV. Notably, a decrease in lung height was observed in patients with impaired pulmonary function, whereas the horizontal and vertical diameters of the lungs remained stable.

Conclusions: In AS patients, TLV was found to be correlated with pulmonary function, particularly parameter such as FVC, FEV1, and TLC. A significant reduction in TLV was observed in those with impaired pulmonary function, with the primary contributing factor being a decrease in lung height.