AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Influence of Morphometry and Airway Constriction on Response to Inhaled Methacholine
MICHAEL OLDHAM, Rodney Clinkenbeard, Owen Moss, University of California, Irvine
Abstract Number: 527 Working Group: Health Related Aerosols
Abstract For some individuals, the degree of response to inhaled allergens or efficacy of inhaled pharmaceuticals may be influenced by their lung morphometry and normal state of airway constriction. Such a relationship was investigated by obtaining lung images before and after human subjects were exposed to a bronco-constrictor.
Fourteen healthy, non-smoking subjects received a computed tomograph (CT) scan just prior to performance of a methacholine challenge. Following the methacholine challenge and bronchodilation all subjects received a second CT scan. CT scans were reconstructed for the first six tracheobronchial airway-generations and airway length, diameter, branch angle and inclination to gravity dimensions were obtained. A typical path airway model of the first six tracheobronchial airway generations was used to calculate airway circumference and surface area. The product of airway circumference and surface area was incorporated into an airway volume factor, inversely proportional to the fractional decrease in airway circumference due to deposited methacholine.
Comparison of airway dimensions from the two CT scans indicated all subjects started the study with each airway generation having some degree of constriction (2% to 33%). Six subjects did not respond to the methacholine challenge while 8 subjects responded with a greater than 3% decrease in their forced expiratory volume in one second. Compared to the non-responders, these responders had smaller airway volume factors (about the same in airway generation 1 to 36% smaller in airway generation 5). They also entered the study with a greater degree of airway constriction (The largest difference was in airway generation 5; 28% compared to 13% constricted in the non-responsive).
All subjects entered the study with upper airway constriction. Eight subjects showed responses that reflected lung morphometry and airway surface dose effects; and six subjects with the smallest normal state of airway constriction and the largest airways did not respond to inhaled methacholine.