Diaphragm excursion and peak oxygen uptake in fibrotic interstitial lung diseases

Background Restrictive ventilatory impairment reduces exercise tolerance in patients with interstitial lung disease (ILD). Studies evaluating the relationship between diaphragmatic function and exercise tolerance in patients with ILD are limited. This study aimed to evaluate diaphragmatic function using ultrasonography and examine its association with exercise tolerance in patients with fibrotic ILD (f-ILD). Patients and Methods Consecutive patients with stable f-ILDs were enrolled. Maximum diaphragmatic excursion (DE max ) during deep breathing was measured using ultrasonography to assess diaphragmatic function. Exercise tolerance was quantified using cardiopulmonary exercise testing (CPET), with peak oxygen uptake (peak VO 2 ) as the primary exercise variable. The association between DE max and peak VO 2 was examined. Results Forty 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 VO 2 (r=0.79, p<0.01). In the multivariable analysis, only DE max remained a significant predictor of peak VO 2 (β=0.65, p<0.001), accounting for 65% of the variance (R 2 =0.66). Conclusions 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.