Heterogeneity of bronchoconstriction does not distinguish mild asthmatic subjects from healthy controls when supine.
Heterogeneity is a fundamental property of airway constriction; however, whether it is a distinguishing feature of mild asthma is not clear. We used computerized tomography and the forced oscillation technique to compare lung heterogeneity between 18 mildly asthmatic and 19 healthy control subjects at similar levels of bronchoconstriction while subjects were supine. We also assessed the effects of deep inhalation and albuterol on supine lung mechanics. Measures of heterogeneity included lung attenuation, from which we derived a novel index of air-space size, and the frequency dependence of respiratory system resistance between 1 and 20 Hz. We found that asthmatic subjects had airways hyperresponsiveness to methacholine in the sitting position compared with controls, but both groups had similar falls in forced expiratory volume in 1 s after inhaling methacholine while supine. There were no baseline differences between the groups in the frequency dependence of resistance, or lung attenuation, before methacholine, and both groups responded similarly with an increase in air-space size (+9.2% vs. +3.4%), air-space size heterogeneity (+9.8% vs. +4.2%), and frequency dependence of resistance (+76% vs. +86%) after methacholine. Deep inhalation did not affect resistance in either group, but albuterol significantly reduced resistance in both groups. We conclude that both computerized tomography and the forced oscillation technique demonstrate increased heterogeneity of airway narrowing during induced bronchoconstriction while supine and that this heterogeneity is equivalent between subjects with mild asthma and healthy controls when bronchoconstricted to the same degree. Thus heterogeneity appears to be a fundamental feature of bronchoconstriction and is not unique to mild asthma.
Kaminsky
David A
DA
Vermont Lung Center, University of Vermont College of Medicine, Burlington, Vermont 05405, USA. david.kaminsky@uvm.edu
Irvin
Charles G
CG
Lundblad
Lennart K A
LK
Thompson-Figueroa
John
J
Klein
Jeffrey
J
Sullivan
Michael J
MJ
Flynn
Frank
F
Lang
Sherburn
S
Bourassa
Lorraine
L
Burns
Stephanie
S
Bates
Jason H T
JH
D000293:Adolescent; D000328:Adult; D000403:Airway Resistance / Q000187:drug effects; D000420:Albuterol / Q000494:pharmacology; D001249:Asthma / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000503:physiopathology; D016535:Bronchial Hyperreactivity / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000503:physiopathology; D001985:Bronchial Provocation Tests; D016084:Bronchoconstriction / Q000187:drug effects; D016085:Bronchoconstrictor Agents; D001993:Bronchodilator Agents / Q000494:pharmacology; D016022:Case-Control Studies; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D001239:Inhalation; D008297:Male; D016210:Methacholine Chloride; D012129:Respiratory Function Tests; D012720:Severity of Illness Index; D013147:Spirometry; D016683:Supine Position; D014057:Tomography, X-Ray Computed
D016085:Bronchoconstrictor Agents; D001993:Bronchodilator Agents; D016210:Methacholine Chloride; D000420:Albuterol