Oscillometry and pulmonary magnetic resonance imaging in asthma and COPD

Abstract

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 3He ventilation‐defect‐percent (VDP) and respiratory‐system resistance, reactance and reactance area (AX) 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 AX (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). AX 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. AX 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.

Applications of oscillometry in clinical research and practice

“…41 Heterogeneous ventilation of the lung correlates with parameters of oscillometry, in particular with the frequency dependence of resistance and the area under the reactance curve (A X ) and, interestingly, also demonstrates some correlation with patient reported outcomes. 18,19 In a recent abstract, it was reported that lung density also appears to be closely correlated to A X , 42 thus lending further support to the notion that heterogeneity, lung density and self-perceived lung health are somehow linked. It would thus appear that regionalization of lung diseases and both the degree and heterogeneity of narrowing in the small airways may be captured using the oscillometry approaches.…”

“…Indeed, there is a great correlation between measures of lung volume and elastance in mouse lungs 13 that corresponds to similar findings in human lungs with ventilation defects, as imaged with MRI and measures of the reactance-area (A X ), defined later in the paper. 18,19 The phenomenon of heterogeneous ventilation of the inflamed human lung has been described previously 20,21 but the novelty discussed at this symposium was that measures of respiratory impedance can correlate with patient reported outcomes. 18 While oscillometry has, thus far, mostly been used in preclinical and clinical research, it is now gaining ground in clinical practice too, with the promise to improve early diagnosis and disease monitoring.…”

“…The difference between R 5 and R 20 is the heterogeneous component of R rs , and the heterogeneity can arise from central or peripheral airways. However, since in most cases of asthma and chronic obstructive pulmonary disease (COPD), these manifest more in the small airways, at least once obstruction is sufficient to increase R rs , and small airway heterogeneity is more commonly the source of R [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] . As a result, the difference between Resistance at 5 Hz (R 5 ) and Resistance at 20 Hz (R 20 ) can pertain to the resistance of the smaller airways.…”

“…As a result, the difference between Resistance at 5 Hz (R 5 ) and Resistance at 20 Hz (R 20 ) can pertain to the resistance of the smaller airways. 13,15,23,[26][27][28] While there has been some debate regarding the interpretations of R [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] in the past, the accumulated evidence is now supportive of interpreting R [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] as reflecting changes in the smaller airways. In a recent publication, using computational modeling and patient data, we show that R 5-20 is a direct measure of airway narrowing and that this correlated with asthma control and quality of life when patients were treated.…”

“…Current data suggest that reported measures of small airways dysfunction such as R [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] are primarily promoted by narrowing within the small airways (more so than by central airways disease) and that heterogeneity is also an important determinant of the measures. 8,40 Furthermore, a quantitative imaging biomarker study suggests that reversal of the normal ventilation gradient in the lung is an important determinant of R [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] . 41 Heterogeneous ventilation of the lung correlates with parameters of oscillometry, in particular with the frequency dependence of resistance and the area under the reactance curve (A X ) and, interestingly, also demonstrates some correlation with patient reported outcomes.…”