Human airway narrowing measured using high resolution computed tomography.

Exaggerated airway narrowing in response to bronchoconstricting stimuli is a characteristic feature of asthmatic subjects. It is unknown whether the site of airway narrowing differs in asthmatic subjects from that observed in normal subjects. Increased airway wall thickness has been suggested as a contributing cause for airway hyperresponsiveness in asthma, based on histologic measurements. We measured airway wall thickness and the site and magnitude of airway narrowing in response to inhaled methacholine in normal subjects and in patients with mild to moderate asthma using high resolution computed tomography (HRCT). After a comparable decrease in FEV1, there were no differences in the site or magnitude of airway narrowing for any category of airway size in asthmatic subjects and normals. However, the results show that the smaller airways of the asthmatic subjects are significantly thickened and that the airway wall area does not change after bronchoconstriction whereas it decreases in normal subjects. We conclude that airway wall thickening and the lack of a change in airway wall dimensions following bronchoconstricting stimuli could contribute to exaggerated airway narrowing in asthma.

Airway narrowing in excised canine lungs measured by high-resolution computed tomography.

The exact site of airway narrowing in asthma and chronic obstructive pulmonary disease is unknown. High-resolution computed tomography (HRCT) is a sensitive noninvasive imaging technique that can be used to measure airway dimensions. After determining the optimal computed tomographic parameters using a phantom, we measured lobe volume and airway dimensions of isolated canine lung lobes at a transpulmonary pressure of 25 cmH2O. These measurements were repeated after deflation and administration of aerosolized saline and carbachol (256 mg/ml). Lobe volume decreased with all treatments. The maximal lobar volume change was 26% at 6 cmH2O after carbachol. Average airway lumen area decreased with all treatments. After carbachol, at transpulmonary pressures of 25, 15, 10, 8, and 6 cmH2O, lumen area decreased by 7.3 +/- 4.1, 62.0 +/- 4.9, 77.5 +/- 3.0, 31.9 +/- 9.0, and 95.2 +/- 1.0% (SE), respectively. When the airways were divided into four categories on the basis of initial lumen diameter (less than 2, 2-4, 4-6, and greater than 6 mm), the greatest decreases in luminal area after carbachol were seen in intermediate-sized airways (2-4 mm, 56 +/- 4%; 4-6 mm, 59 +/- 3%). HRCT can be used to make accurate measurements of airway dimensions and airway narrowing in excised lungs. HRCT may allow measurement of airway wall thickness and determination of the site of airway narrowing in asthma.