title: Effect of airway smooth muscle tone on airway distensibility measured by the forced oscillation technique in adults with asthma.
abstract: Airway distensibility appears to be unaffected by airway smooth muscle (ASM) tone, despite the influence of ASM tone on the airway diameter-pressure relationship. This discrepancy may be because the greatest effect of ASM tone on airway diameter-pressure behavior occurs at low transpulmonary pressures, i.e., low lung volumes, which has not been investigated. Our study aimed to determine the contribution of ASM tone to airway distensibility, as assessed via the forced oscillation technique (FOT), across all lung volumes with a specific focus on low lung volumes. We also investigated the accompanying influence of ASM tone on peripheral airway closure and heterogeneity inferred from the reactance versus lung volume relationship. Respiratory system conductance and reactance were measured using FOT across the entire lung volume range in 22 asthma subjects and 19 healthy controls before and after bronchodilator. Airway distensibility (slope of conductance vs. lung volume) was calculated at residual volume (RV), functional residual capacity (FRC), and total lung capacity. At baseline, airway distensibility was significantly lower in subjects with asthma at all lung volumes. After bronchodilator, distensibility significantly increased at RV (64.8%, P < 0.001) and at FRC (61.8%, P < 0.01) in subjects with asthma but not in control subjects. The increased distensibility at RV and FRC in asthma were not associated with the accompanying changes in the reactance versus lung volume relationship. Our findings demonstrate that, at low lung volumes, ASM tone reduces airway distensibility in adults with asthma, independent of changes in airway closure and heterogeneity.
authors.affiliation: Department of Medicine, Nursing and Health Sciences, Monash University, Clayton, Victoria, Australia. vjkelly@partners.org
authors.forename: Vanessa J
authors.initials: VJ
authors.lastname: Kelly
authors.forename: Nathan J
authors.initials: NJ
authors.lastname: Brown
authors.forename: Scott A
authors.initials: SA
authors.lastname: Sands
authors.forename: Brigitte M
authors.initials: BM
authors.lastname: Borg
authors.forename: Gregory G
authors.initials: GG
authors.lastname: King
authors.forename: Bruce R
authors.initials: BR
authors.lastname: Thompson
mesh_terms: D000328:Adult; D056151:Airway Remodeling; D000403:Airway Resistance; D000704:Analysis of Variance; D001249:Asthma / Q000175:diagnosis* / Q000188:drug therapy / Q000503:physiopathology; D016085:Bronchoconstrictor Agents / Q000627:therapeutic use; D016022:Case-Control Studies; D005260:Female; D005541:Forced Expiratory Volume; D005652:Functional Residual Capacity; D006801:Humans; D008168:Lung / Q000187:drug effects / Q000503:physiopathology*; D008170:Lung Compliance; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D009130:Muscle, Smooth / Q000187:drug effects / Q000503:physiopathology*; D010991:Plethysmography; D011237:Predictive Value of Tests; D012044:Regression Analysis; D012129:Respiratory Function Tests; D013147:Spirometry; D014109:Total Lung Capacity; D014739:Victoria
chemical_list: D016085:Bronchoconstrictor Agents