Abstract:
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Purpose: Exaggerated airway narrowing is arguably the most important and fundamental pathophysiologic abnormality of asthma and has been associated with an increased risk of severe asthma attacks. Lutchen and colleagues and Thorpe and Bates concluded that in the presence of widespread peripheral airway narrowing, lung resistance and elastance were highly sensitive to inhomogeneous narrowing in which a few large airways were highly constricted or nearly closed. This implies that when there is generalised airway narrowing, the added excessive narrowing or closure of one or more large airways leads to a profound increase in lung resistance.
Methods and Materials: A technique has been developed for the safe, effective and highly reproducible assessment of serial and parallel airway heterogeneity using measurement of airway internal volume (Vi) through the use of high resolution, helical multislice computed tomography, together with custom written algorithms for semi-automated image analysis.
Results: We measured heterogeneity of airway narrowing in 4 normal and 7 asthmatic subjects from 1 mm thickness HRCT images obtained before and after methacholine induced airway narrowing. Airway branch points were used as anatomical references for comparisons of changes in airway volumes between parallel airways (arising from the same parent airway) and serial airways (parent/child airways). A threshold method was used to measure the airway lumen area and the airway volume was calculated as the sum of areas from contiguous slices along the whole measurable airway length. Narrowing was expressed as the difference in lumen volume as percent of baseline. Serial and parallel heterogeneity were defined as the differences in percent narrowing between parent and daughter airways, and between sister airways, respectively, with mean differences compared using paired T-tests. The mean change in respiratory resistance and one second forced expiratory volume were 93% and 30% respectively in normals, and 68% and 29% respectively, in asthmatics. In normals and asthmatics, the mean differences in percent narrowing in serial airways were 11+/-2% and 31+/-12%, respectively (p=0.02) and in parallel airways were 11+/-6% and 36+/-13%, respectively (p=0.01).
Conclusion: We conclude that narrowing is more heterogeneous between serial and parallel airways in asthmatic subjects than in normal subjects. Further research is required to determine the clinical significance of such findings.
Magnussen MBBS, PhD, J,
Imaging and Analysis of Airway Heterogeneity in Asthmatics and Normals Using High-Resolution, Multi-Slice Computed Tomography. Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL.
http://archive.rsna.org/2003/3106016.html
