Correlation of diaphragmatic mobility and thickening assessed by lung ultrasound with severity of interstitial lung disease

ABSTRACT Background: Studies conducted in interstitial lung disease (ILD) patients to assess diaphragmatic excursion and thickening fraction suggest a weak to strong correlation with pulmonary function parameters. However, diaphragmatic excursion velocity, a novel imaging marker, has not been correlated with pulmonary function and high-resolution computed tomography (HRCT) fibrosis score in ILD patients previously. Methods: We conducted a cross-sectional analytical study in 40 ILD patients during quiet (QB) and deep breathing (DB) to measure diaphragmatic thickening, excursion and excursion velocity using transthoracic ultrasound and correlated them with pulmonary function parameters and HRCT fibrosis score. Results: Most diaphragm parameters in DB correlated more strongly with lung function parameters compared to quiet breathing. Right diaphragmatic excursion, during QB and DB, showed positive correlations with forced vital capacity (FVC) z -score ( r = 0.591, 0.676) and diffusion capacity of the lung for carbon monoxide (DL CO ) z -score ( r = 0.437, 0.438), and negative correlations with HRCT fibrosis score ( r = −0.439, −0.425), respectively. In addition, right diaphragmatic velocity exhibited positive correlations with FVC z -score ( r = 0.388, 0.667) and DL CO z -score ( r = 0.139, 0.412), and negative correlations with HRCT fibrosis score ( r = −0.454, −0.445). Right diaphragm thickening fraction showed positive correlations with FVC z -score ( r = 0.330, 0.460) and DL CO z -score ( r = 0.400, 0.426), and negative correlations with HRCT fibrosis score ( r = −0.199, −0.237). Similarly, right diaphragmatic thickness indicated positive correlations with FVC z -score ( r = 0.526, 0.614) and DL CO z -score ( r = 0.298, 0.298), and negative correlations with HRCT fibrosis score ( r = −0.398, −0.401). Conclusion: Diaphragmatic excursion velocity during DB showed a weak to moderate correlation with pulmonary function parameters and HRCT fibrosis score and may be utilized as a surrogate marker in ILD patients unable to perform pulmonary function tests or undergo sequential HRCT thorax in follow-up.