Oscillation mechanics of the human lung periphery in asthma

Abstract

To more precisely measure the mechanical properties of the lung periphery in asthma, we have developed a forced oscillation technique that applies a broad-band flow signal through a wedged bronchoscope. We interpreted the data from four healthy and eight mildly asthmatic subjects in terms of an anatomically accurate computer model of the wedged segment. There was substantial overlap in impedance between the two groups, with resistance (R) showing minimal frequency dependence and elastance (E) showing positive and negative frequency dependence across subjects. After direct instillation of methacholine, R rose in both groups, but compared with healthy subjects, the asthmatic subjects displayed upward, parallel shifts in their dose-response curves. The baseline frequency-response patterns of E were enhanced after methacholine. Frequency dependencies of R and E were well reproduced in two normal subjects by a computational model that employed rigid airways connected to constant-phase tissue units but were better reproduced in the other two normal and three asthmatic subjects when the model employed heterogeneous, peripheral airway narrowing and compliant airways. To capture the frequency dependencies of R and E in the remaining five asthmatic subjects, the model was modified by increasing airway wall stiffness. These results indicate that the lung periphery of mildly asthmatic subjects is not well distinguished from that of healthy subjects by measurement of mechanical impedance at baseline, but group differences are seen after challenge with methacholine. Modeling of the response suggests that variable contributions of airway narrowing and wall compliance are operative in determining overall mechanical impedance of the lung periphery in humans with asthma, likely reflecting the functional consequences of airway inflammation and remodeling.

What Does Airway Resistance Tell Us About Lung Function?

“…55 In a different study, Kaminsky and colleagues have uniquely demonstrated hyper-responsiveness of the lung periphery in participants with asthma using the FOT. 66 Because interpretation of Z RS depends on lung models, the technique yields information in relation to such models, and therefore is also limited by the properties of the model in use. 67 …”

Airway impedance entropy and exacerbations in severe asthma

“…A variety of measures of airway calibre were derived from the mean values of the 750 data points captured (table 1): 1) R at 20 Hz (R20), which we interpret as a measure of the mean level of airway constriction within the bronchial tree; 2) R at 5 Hz (R5) minus R20 (R5-R20), which we interpret as a measure of the heterogeneity of airway narrowing throughout the bronchial tree [21]; and 3) the area under the curve of the reactance spectrum between 5 Hz and resonant frequency (reactance area; AX), which we interpret as a measure of the heterogeneity of airway closure throughout the bronchial tree [22].…”

Update on the roles of distal airways in asthma

“…This method is particularly attractive in children as it requires only passive cooperation from the subject, who breathes quietly at tidal volume during the test. A predominant increase of Rrs at low frequencies (,10-15 Hz) called frequency dependence has been shown to reflect obstruction in distal airways in various obstructive lung diseases, including asthma [87][88][89][90][91]. Low frequency Rrs were increased in asthmatic children with mild airway obstruction (FEV1 .80% pred and FEF25-75% ,80% pred) [92].…”