Novel Advanced Impedance Metrics on Impedance-pH Testing Predict Lung Function Decline in Idiopathic Pulmonary Fibrosis

Abstract

Introduction: Gastroesophageal reflux has been associated with idiopathic pulmonary fibrosis (IPF). Mean nocturnal baseline impedance (MNBI) is a marker of esophageal mucosal integrity, whereas postreflux swallow-induced peristaltic wave (PSPW) index reflects esophageal chemical clearance. Both metrics offer novel ways to assess reflux burden on multichannel intraluminal impedance-pH testing (MII-pH), but their role in extraesophageal reflux remains unclear. We aimed to evaluate the relationship between these novel metrics and lung function decline in patients with IPF.

Methods: Adults with IPF undergoing prelung transplant MII-pH were enrolled. All patients completed pulmonary function testing (PFT) at the time of MII-pH and at the 1-year follow-up. MNBI was calculated by averaging baseline impedance at three 10-minute intervals (1 AM/2 AM/3 AM). PSPW index was the proportion of all reflux episodes, followed by a peristaltic swallow within 30 seconds. Univariate (Student t-test/Pearson correlation) and multivariable (general linear regression) analyses were performed.

Results: One hundred twenty-five subjects (mean age = 61.7 years, 62% men) were included. Forced expiratory volume in one second and forced vital capacity declined more significantly over 12 months in subjects with lower distal MNBI, proximal MNBI, and PSPW index (all P < 0.05). On multivariable analyses adjusting for age, sex, proton pump inhibitor use, and baseline lung function, distal MNBI (β = -10.86, P = 0.024; β = -8.03, P = 0.045), proximal MNBI (β = -13.5, P = 0.0068; β = -9.80, P = 0.025), and PSPW index (β = -18.1, P = 0.010; β = -12.55, P = 0.050) remained predictive of greater forced expiratory volume in one second and forced vital capacity decline.

Discussion: Low distal MNBI, proximal MNBI, and PSPW index independently predicted more severe lung function decline over 1 year in patients with IPF. These impedance metrics may have prognostic value and support a role for reflux in IPF pathogenesis.