Influence of Morphometry and Airway Patency on Response to Inhaled Methacholine

Abstract

For some individuals, the degree of response to inhaled allergens or the efficacy of inhaled pharmaceuticals may be influenced by their lung morphometry. Fourteen healthy, nonsmoking subjects received a high-resolution computed tomography (HRCT) scan just prior to performance of a methacholine challenge. Following the methacholine challenge, subjects were given a bronchodilator and received a second HRCT scan. HRCT scans were reconstructed and measurements of airway length, diameter, branch angle, and inclination to gravity were made for the first six tracheobronchial airway generations. The average length (L) and diameter (d) of each airway generation were used to calculate the average airway generation circumference (πd) and surface area (πLd). The product of airway circumference and surface area was incorporated into an airway volume factor (Ld2 ), inversely proportional to the fractional decrease in airway circumference due to deposited methacholine. Ld2 was used to compare methacholine challenge resp...