Diaphragm assessment by multimodal ultrasound imaging in patients with interstitial lung disease: a prospective observational study.

BACKGROUND

The dyspnea experienced by patients with interstitial lung disease (ILD) is partly attributable to diaphragmatic dysfunction. This study aims to quantitatively evaluate diaphragmatic function in ILD patients by measuring different diaphragm ultrasound parameters, seeking to gain a more comprehensive understanding of diaphragmatic characteristics in this population.

METHODS

Forty-four ILD patients and 31 healthy controls were prospectively enrolled and underwent diaphragmatic ultrasound. Parameters measured included diaphragmatic thickness, excursion, and tissue Doppler imaging (TDI)-derived acceleration and velocity. Intra-operator reliability of ultrasound measurements was validated using intraclass correlation coefficient (ICC) and Bland-Altman analysis, and multivariate regression analysis was performed to adjust for confounding factors. Correlations between ultrasound parameters and clinical/pulmonary function indices were analyzed.

RESULTS

Compared with controls, ILD patients had greater diaphragmatic thickness during quiet breathing (QB) (end-expiration 0.21 vs. 0.17 cm, P=0.004), significantly reduced thickening fraction (TF) (46.89% vs. 114.29%, P<0.001), and decreased deep breathing (DB) excursion (3.19 vs. 6.24 cm, P<0.001). TDI showed higher peak relaxation velocity (1.87 vs. 1.60 cm/s, P=0.02), contraction acceleration (3.80 vs. 2.68 cm/s2, P=0.02), and relaxation acceleration (5.27 vs. 3.04 cm/s2, P<0.001) in ILD patients. TF and excursion negatively correlated with St George's Respiratory Questionnaire (SGRQ) scores, modified Medical Research Council Dyspnoea Scale (mMRC) grades, and serum Krebs von der Lungen 6 (KL-6) levels, but positively correlated with pulmonary function. Diaphragmatic acceleration positively associated with SGRQ scores/mMRC grades and negatively with pulmonary function.

CONCLUSIONS

Multimodal ultrasound allows for the evaluation of diaphragmatic function in patients with ILD. ILD patients exhibit diaphragmatic structural and functional abnormalities (thickening, reduced contractility/excursion, increased activation) that correlate with clinical indicators of disease severity. As a non-invasive tool, diaphragmatic ultrasound parameters may provide a reference for assessing respiratory function-related outcomes in ILD patients, though direct evidence linking these parameters to respiratory function is lacking. Given the moderate sample size and cross-sectional design of this study, the clinical utility of these ultrasound parameters requires validation in larger, prospective cohorts.