Investigation of the correlation between the change in the projected lung area and forced vital capacity using biphasic chest dynamic digital radiography: a cross-sectional study.

Background: Chest dynamic digital radiography (DDR) is used as a supplementary tool for the routine pulmonary function test (PFT); however, its potential as a novel standard PFT method has yet to be explored. Therefore, the present study aimed to investigate the correlation between the change in the projected lung area (ΔPLA) and forced vital capacity (FVC) using chest DDR, and to establish a DDR-FVC estimation model and a predictive value model for the ΔPLA. Methods: In total, 139 participants who underwent chest DDR and the PFT in the same period at The First Affiliated Hospital of Guangzhou Medical University from April 2022 to February 2023 were prospectively included in the study. The patients' age, gender, height, and weight measurements were recorded. Additionally, the ΔPLA was measured, and the IWS workstation software was used for automated outlining and calculation. Subsequently, a correlation analysis and regression analysis models were employed to examine the relationship between the ΔPLA, FVC, and individual physiological characteristics. Additionally, an independent sample Results: The 139 participants were grouped according to the results of the ratio of measured/predicted FVC values (FVC%pred); those with an FVC%pred ≥80%, were allocated to the normal FVC group, and those with an FVC%pred <80% were allocated to the abnormal FVC group. The correlation coefficient was >0.8 in the full sample; the ΔPLA showed a significant linear correlation with the measured FVC value [r=0.81, 95% confidence interval (CI): 0.75-0.86, P<0.001]. There was a significant difference in the ΔPLA between the normal and abnormal FVC groups. With the ΔPLA, age, gender, height, and weight as predictor variables, the following DDR-FVC estimation model was established: DDR-FVC estimation model = -0.997 + 1.35×10 Conclusions: There was a linear correlation between the ΔPLA measured by biphasic chest DDR and the FVC. A model for estimating the FVC was established based on the ΔPLA, which allows the FVC to be assessed by the ΔPLA measured by biphasic chest DDR. A predictive value model for the ΔPLA was also established to provide ΔPLA reference values for assessment and comparison.