Diaphragm excursion and peak oxygen uptake in fibrotic interstitial lung diseases

Restrictive ventilatory impairment reduces exercise capacity in patients with interstitial lung disease (ILD). A limited number of studies have evaluated the relationship between diaphragmatic function and exercise capacity in patients with ILD. This study aimed to evaluate diaphragmatic function using ultrasonography and examine its association with exercise capacity in patients with fibrotic ILD (f-ILD).

Consecutive patients with stable f-ILD were enrolled. Maximum diaphragmatic excursion (DE_max) during deep breathing was measured using ultrasonography to assess diaphragmatic function. Exercise capacity was quantified using cardiopulmonary exercise testing (CPET), with peak oxygen uptake (peak V'_O2 ) as the primary exercise variable. The association between DE_max and peak V'_O2 was examined.

40 consecutive patients with f-ILD were included (mean age 76.7±6.3 years). DE_max was significantly correlated with forced vital capacity (r=0.54; p<0.01), diffusing capacity of the lung for carbon monoxide (r=0.54; p<0.01), maximum inspiratory pressure (r=0.58; p<0.01) and peak V'_O2 (r=0.79; p<0.01). In the multivariable analysis, only DE_max remained a significant predictor of peak V'_O2 (β=0.65; p<0.001), accounting for 65% of the variance (R²=0.66).

In patients with f-ILD, DE_max measured using ultrasonography was independently associated with exercise capacity assessed using CPET. These findings suggest that DE_max may serve as a useful physiological marker related to exercise performance in this patient population.