Oscillometry and pulmonary magnetic resonance imaging in asthma and COPD

Developed over six decades ago, pulmonary oscillometry has re‐emerged as a noninvasive and effort‐independent method for evaluating respiratory‐system impedance in patients with obstructive lung disease. Here, we evaluated the relationships between hyperpolarized (3)He ventilation‐defect‐percent (VDP) and respiratory‐system resistance, reactance and reactance area (A(X)) measurements in 175 participants including 42 never‐smokers without respiratory disease, 56 ex‐smokers with chronic‐obstructive‐pulmonary‐disease (COPD), 28 ex‐smokers without COPD and 49 asthmatic never‐smokers. COPD participants were dichotomized based on x‐ray computed‐tomography (CT) evidence of emphysema (relative‐area CT‐density‐histogram ≤ 950HU (RA (950)) ≥ 6.8%). In asthma and COPD subgroups, MRI VDP was significantly related to the frequency‐dependence of resistance (R (5‐19); asthma: ρ = 0.48, P = 0.0005; COPD: ρ = 0.45, P = 0.0004), reactance at 5 Hz (X (5): asthma, ρ = −0.41, P = 0.004; COPD: ρ = −0.38, P = 0.004) and A(X) (asthma: ρ = 0.47, P = 0.0007; COPD: ρ = 0.43, P = 0.0009). MRI VDP was also significantly related to R (5‐19) in COPD participants without emphysema (ρ = 0.54, P = 0.008), and to X (5) in COPD participants with emphysema (ρ = −0.36, P = 0.04). A(X) was weakly related to VDP in asthma (ρ = 0.47, P = 0.0007) and COPD participants with (ρ = 0.39, P = 0.02) and without (ρ = 0.43, P = 0.04) emphysema. A(X) is sensitive to obstruction but not specific to the type of obstruction, whereas the different relationships for MRI VDP with R (5‐19) and X (5) may reflect the different airway and parenchymal disease‐specific biomechanical abnormalities that lead to ventilation defects.