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.
BackgroundRecent advances in bronchoscopy, such as transbronchial biopsy (TBB) using endobronchial ultrasonography with a guide sheath (EBUS-GS), have improved the diagnostic yield of small-sized peripheral lung lesions. In some cases, however, it is difficult to obtain adequate biopsy samples for pathological diagnosis. Adequate prediction of the diagnostic accuracy of TBB with EBUS-GS is important before deciding whether bronchoscopy should be performed.MethodsWe retrospectively reviewed 149 consecutive patients who underwent TBB with EBUS-GS for small-sized peripheral lung lesions (≤30 mm in diameter) from April 2012 to March 2013. We conducted an exploratory analysis to identify clinical factors that can predict an accurate diagnosis by TBB with EBUS-GS. All patients underwent thin-section chest computed tomography (CT) scans (0.5-mm slices), and the CT bronchus sign was evaluated before bronchoscopy in a group discussion. The final diagnoses were pathologically or clinically confirmed in all studied patients (malignant lesions, 110 patients; benign lesions, 39 patients).ResultsThe total diagnostic yield in this study was 72.5 % (95 % confidence interval: 64.8–79.0 %). Lesion size, lesion visibility on chest X-ray, and classification of the CT bronchus sign were factors significantly associated with the definitive biopsy result in the univariate analysis. In the multivariate analysis, only the CT bronchus sign remained as a significant predictive factor for successful bronchoscopic diagnosis. The CT bronchus sign was also significantly associated with the EBUS findings of the lesions.ConclusionOur results suggest that the CT bronchus sign is a powerful predictive factor for successful TBB with EBUS-GS.
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.
There is increasing interest in the structural components of the airway wall because of the airway remodeling that is observed in conditions such as asthma and chronic obstructive pulmonary disease and because of their contribution to changes in airway mechanics. This interest has stimulated several groups to make morphometric measurements on airway cross sections, and their results have been reported using a variety of nomenclature. We propose the adoption of a standard system of nomenclature that is based on accepted terms for subdivisions of the airway wall and has been agreed to by several groups working in this field.
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