Tomographic assessment of airways in subjects without respiratory disorders

Abstract

Objectives: Airway remodeling is found in many respiratory disorders and it probably has an influence on clinical presentation and natural history of those diseases. Epithelium, smooth muscle and extracellular matrix may be abnormal in airways of subjects with asthma and chronic obstructive pulmonary disease (COPD). The "gold standard" method to diagnose remodeling is histopathology, but it is too invasive to be used frequently in research or clinical practice. Quantitative computed tomography (CT) assessment is much safer and may provide information concerning anatomic abnormalities of the airways. Many researchers have shown correlations between quantitative CT measurements, pulmonary function tests and clinical aspects of diseases like asthma, COPD and cystic fibrosis. Those studies often encompass control groups (healthy subjects) but there are no well established normal values for airway quantitative CT findings, unlike what exists regarding induced sputum and spirometry. The aims of this study are to assess if airway CT parameters conform to a normal distribution, to establish reference values for our population and to create a "historical control" group to be used in further research in our institution. METHODS: We have a database that comprises records of all patients who underwent CT and spirometry at Ribeirão Preto Medical School Hospital, University of São Paulo and the dates of each evaluation during the years 2012 and 2013 (601 patients).We will select the cases in which time between spirometry and CT was less than 4 weeks and study the medical reports of those, selecting patients between 18 and 60 years old with no respiratory symptoms, who had smoked less than 10 pack-years and were non-smokers by the time of the evaluations and had had no respiratory infections during 4 weeks before radiologic and spirometric assessments (many patients undergo the assessments according to specific protocols, without any sign of respiratory disorders).Quantitative CT analysis will be performed using Yacta, a software installed at the Radiology Center of our Institution. Even old images may be downloaded and analyzed: the software segmentates the airways and measures total diameter, lumen area, wall thickness, percentual wall thickness, maximum attenuation of wall (in Hounsfield units) of different generations of airways. We will use Kolmogorov-Smirnoff test to evaluate the goodness of fit to normal distribution of each CT parameter. We will then obtain the proper central tendency and dispersion measurements based on the distribution we will find.