Strain analysis based on dynamic ventilation computed tomography in fibrotic interstitial lung disease and its correlation with pulmonary function tests.

Background: Fibrotic interstitial lung disease (fILD) consists of a heterogeneous group of chronic, progressive interstitial lung diseases characterized by reduced lung elasticity and restrictive ventilatory impairment. Strain analysis based on dynamic ventilation computed tomography (DVCT) has emerged as a novel method for quantifying lung deformation during ventilation and thus monitoring the pathophysiological changes in lungs. This study aimed to quantitatively identify abnormal lung motion in patients with fILD through use of strain analysis and to determine the correlation of these values with spirometric indices. Methods: A total of 27 patients with fILD and 20 healthy controls were prospectively recruited. All participants underwent DVCT scanning on a 320-row computed tomography (CT) scanner. Strain metrics across the full respiratory cycle were computed with computational fluid dynamics software at nine axial levels spanning the upper, middle, and lower lungs. In patients, the percentage of fibrotic lung at the corresponding levels was also quantified. Group differences were assessed, and Pearson correlations were used to determine the associations between strain metrics, percentage fibrosis, and pulmonary function parameters. Results: During the respiratory cycle, lung strain exhibited heterogeneous temporal and spatial distributions. There were significant differences in maximum principal strain, mean principal strain, maximum displacement speed, and mean displacement speed between the upper, middle, and lower parts of both lungs, both in patients and controls (P<0.05). In both groups, peaks in strain were observed during the early expiration and mid-inspiration phases. Patients with fILD exhibited a distinct pattern, with consistently lower strain values across all metrics, while those of healthy controls were all significantly higher. The strain-related parameters were significantly correlated with forced expiratory volume at 1 second (r: 0.646-0.769; P≤0.001), forced vital capacity (r: 0.670-0.827; P≤0.001), and total lung capacity (r: 0.625-0.817; P≤0.001), whereas the percentage of lung fibrosis was not associated with any other parameters. Conclusions: DVCT-derived strain represents a quantitative measure of abnormal regional lung motion in patients with fILD and may complement spirometry by capturing local ventilatory mechanics. This technique shows promise for the evaluation of regional mechanical impairment in patients with fibrotic lung disease.