The sensitivity of different lung function metrics to detect airways disease

Sensitive metrics to diagnose airways disease are lacking. Spirometry is widely used, yet is relatively insensitive to detect early disease. The NOVELTY ADpro study aims to phenotype airways disease using ¹²⁹Xe-MRI, spirometry, airwave oscillometry (AOS), lung clearance index (LCI), body plethysmography and TLco, in patients with asthma and/or COPD. ¹²⁹Xe ventilation MRI is highly sensitive to early disease and here is used as a reference to compare against the sensitivities of common metrics to detect lung abnormality (defined as a value <lower or >upper limit of normal). Of 143 patients (51.7% = female, mean [SD] age = 58.9 (12.8) years), evidence of airways disease was present in 72.0% based on abnormal ¹²⁹Xe-MRI ventilation defect percent (VDP), in 46.9% on FEV1/FVC and in 20.3% on FEV1. In comparison, LCI was abnormal in 69.2%, AOS in 55.2% and 18.9% for both RV/TLC and TLco. From AOS, the resistance (R) at 5Hz was abnormal in 37.1%, 39.2% for R5-R20, 38.5% for reactance (X) at 5Hz and 43.4% for reactance area (AX). Of 67 patients with abnormal FEV1/FVC, 16 had normal AOS and of 79 patients with abnormal AOS, 28 had normal spirometry. When combined, AOS and spirometry detected airways disease in 66.4% of patients. Traditional spirometric measures showed poor sensitivity for significant ventilation abnormalities on ¹²⁹Xe-MRI in patients with asthma and/or COPD. LCI gives similar high sensitivity to ¹²⁹Xe-MRI VDP but is a complex specialist test reserved for tertiary centres. AOS requires only tidal breathing, is portable, quick to perform and offers complimentary diagnostic information to spirometry; the two tests could be combined when screening for airways disease.