In: Bronchiolitis9 Apr 2014
In our study, air trapping as detected on expiratory HRCT was the best indicator of BO after lung transplantation with a sensitivity of 91%, specificity of 80%, and accuracy of 85%, respectively. We identified air trapping in two patients with BO and BOS, stage 0 (FEV1 >80% baseline). In one of these patients, results of all pulmonary function tests, including early indexes of airway obstruction such as FEF50/FVC ratio and FEF25_Y5, were normal; air trapping on expiratory HRCT was the only demonstrable evidence of early airways disease other than the abnormal transbronchial biopsy specimen.
We did not identify a significant correlation between CT score of air trapping and BOS stage in our 11 patients with documented BO. Using a dynamic CT technique in a series of nine patients with obstructive lung disease, Stem and colleagues showed excellent correlation (r=— 0.92) between extent of air trapping and FEY,. The discrepant results between the two studies likely relate to differences in method. Although all patients in our study were instructed and coached to “blow out all the way and then hold your breath” in an attempt to acquire expiratory images consistently at residual volume, intrapatient and interpatient variations in postexpiratoiy lung volumes and some motion artifact likely contributed to inaccurate estimations of extent of air trapping. More reproducible and consistent postexpiratory lung volumes were likely elicited by Stern et aln who acquired a series of ten 100-ms images over a 6-s period during a forced inspiratory and expiratory vital capacity maneuver on an electron-beam CT scanner.
Our study was limited by the small number of patients included and the heterogeneous nature of the BO study group which included patients with both early and well-established disease. However, despite these limitations and our inability to acquire expiratory images at a consistent lung volume, our results suggest that expiratory HRCT may be a useful technique in the detection of BO in the lung transplant population. Air trapping was found to be the most accurate radiologic indicator of BO, and preceded development of measurable lung dysfunction in one patient with pathologically proved BO. The role of expiratory HRCT in the detection of early, preclinically evident BO remains to be investigated by future prospective studies which optimally would be performed on CT scanners with spiromet-ric gating capabilities.
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