The potential clinical implications of slow vital capacity in patients with idiopathic pulmonary fibrosis

Abstract Idiopathic pulmonary fibrosis (IPF) is a progressive interstitial lung disease with a highly variable clinical course. Forced vital capacity (FVC) is widely used as a marker of disease severity and progression, yet its variability and dependence on patient effort raise concerns regarding its reliability. Given these limitations, we investigated the clinical significance of slow vital capacity (SVC) as a potential alternative measure of lung function in IPF. In a retrospective cohort of 89 IPF patients who underwent pulmonary function testing with concomitant SVC measurements, we observed a strong correlation between FVC and SVC (r = 0.973 at baseline, r = 0.978 at follow-up). However, in 99% of cases, SVC values were equal to or exceeded FVC, and follow-up assessments revealed that FVC exhibited greater variability than SVC. Notably, patients with a decrease in SVC demonstrated worse survival outcomes, whereas FVC decline did not show the same prognostic significance. These findings suggest that SVC may provide a more stable and clinically meaningful measure of disease progression in IPF. Moreover, its less effort-dependent nature could improve reproducibility, particularly in patients with advanced diseases. Our study highlights the potential role of SVC as a valuable metric in clinical practice and as an endpoint in future IPF trials. Prospective validation of these findings could further establish SVC as a superior tool for disease monitoring and therapeutic assessment.