Introduction: Sarcoidosis is physiologically heterogeneous, frequently manifesting with obstruction or isolated impairments in gas exchange rather than restriction. We hypothesize that respiratory oscillometry, which captures ventilation heterogeneity, lung compliance, and small airways disease, may be a more sensitive single marker of physiologic impairment than forced vital capacity (FVC).

Objectives: To characterize the frequency and clinical characteristics of isolated impaired oscillometry and assess the discriminative ability of oscillometry for impaired health-related quality of life (HrQOL) as compared to conventional pulmonary function tests (PFTs). 

Materials and Methods: Participants with biopsy-proven sarcoidosis on immunosuppression in a prospective cohort underwent oscillometry and spirometry testing according to ATS/ERS guidelines. Associations between oscillometric parameters and HrQOL measures (St. George’s Respiratory Questionnaire [SGRQ], modified Medical Research Council [mMRC], and King’s Sarcoidosis Questionnaire [KSQ]) were tested in multivariable linear regression (ordinal logistic regression for mMRC), adjusted for gender, race, disease duration, and Charlson Comorbidity Index (CCI). Participants were classified into pulmonary function phenotypes using Global Lung Function Initiative-defined lower limit of normal, categorized as normal, obstruction, restriction, isolated reduced DLCO, and isolated impaired oscillometry (at least one abnormal oscillometry parameter). Area under the receiver operating curve for discrimination of mMRC<2 and SGRQ<25 was calculated for oscillometry, spirometry, and DLCO. 

Results: The demographic and clinical characteristics of the cohort are shown in Table 1. Four participants with isolated oscillometry impairment had a shorter disease duration[EC1.1] and similar HrQOL to other PFT-defined categories. Oscillometry parameters, but not FVC, were significantly associated with impaired SGRQ and mMRC (Table 2). No parameter was associated with KSQ. Discrimination of impaired HrQOL by AUROC was similar for oscillometry as for conventional PFTs.  

Conclusions: Respiratory oscillometry demonstrated discriminative accuracy for HrQOL comparable to conventional PFTs. In some cases, respiratory physiology may be impaired in sarcoidosis even in the setting of normal PFTs, and may therefore be useful for early disease detection.