Comparison of Idiopathic Interstitial Pneumonia and Connective Tissue Disease Related Interstitial Lung Disease by Physiologic and Functional Testing Parameters

Document Type

Conference Proceeding

Publication Date


Publication Title

Am J Respir Crit Care Med


Introduction: Pulmonary function tests (PFTs) and six minute walk tests(6MWTs) in Idiopathic Interstitial Pneumonias (IIP) and Connective Tissue Disease related Interstitial Lung Disease (CTD-ILD) provide a baseline for longitudinal care and functional assessment. This retrospective, cross-sectional study was designed to characterize differences in physiologic and functional parameters among patients with IIP or CTD-ILD. Methods: Electronic medical records were used to identify patients evaluated in the Henry Ford Hospital Pulmonary Clinics for ILD (identified via International Classification of Diseases 9 code for ILD) and had undergone forced vital capacity (FVC) and diffusing capacity of carbon monoxide (DLCO) between January 1st, 2010 and August 31st, 2015. Patients who did not have a 6MWT within 90 days of a selected PFT and an echocardiogram within 180 days of a matched pair of PFT and 6MWT were excluded. Patients with echocardiographic features of pulmonary hypertension or systolic dysfunction were also excluded. Demographic variables and results from diagnostic testing (PFT and 6MWT performed according to ATS criteria) and echocardiogram were collected. Mean values and percentages were calculated for linear and categorical variables. Two-sample t-tests were performed for continuous variables comparing the IIP and CTD-ILD groups. Linear regression analysis of %predicted DLCO adjusted for hemoglobin (%pred adjDLCO) with degree of desaturation on 6MWT by group was performed. Results: Forty-two of the 438 ILD patients who underwent PFTs, 6MWT and echocardiogram met full inclusion criteria: 24 with IIP and 18 with CTD-ILD. Patients with IIP were older (mean age 63 years) than those with CTD-ILD (mean age 50 years). The majority of patients with IIP were male (75%) while only 33.3% of the CTD-ILD group were male. Despite similar mean %pred adjDLCO, more patients with IIP (45.8%) required supplemental oxygen, compared to 22.2% of CTD-ILD patients. There were no significant differences in mean %predicted FVC, baseline Borg dyspnea or fatigue scores, or degree of desaturation on 6MWT between the two groups. There was no significant correlation of %pred adjDLCO with change in oxygen saturation during 6MWT for the IIP or CTD-ILD groups, after control for amount of supplemental oxygen worn. Conclusions: In this single center cohort of IIP and CTD-ILD patients, the %pred adjDLCO did not correlate with the degree of desaturation during 6MWT, despite a higher percentage of patients with IIP requiring supplemental oxygen. Small sample size and use of supplemental oxygen during 6MWT in about 1/3 of the patients may have influenced our findings.

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