High-resolution Computed Tomography (HRCT) Evaluation of Airway Distensibility in Lung Transplant Recipients

Chest CT imaging will be obtained in the radiology department at UTMB. After the initial screening visit, subjects will visit the pulmonary function laboratory where they will undergo spirometry and measurement of lung volumes by whole body plethysmography. Within two hours of pulmonary function testing, subjects will undergo an initial HRCT scan. After the initial HRCT, subjects will inhale a standard dose of ipratropium bromide (0.5 mg) using a hand held nebulizer. Thirty minutes after ipratropium bromide administration, spirometry will be measured followed by a second HRCT scan.

Spirometry measurements will be performed in triplicate with the subjects in a seated position using a portable Koko spirometer (PDS, Louisville, CO). After the spirometry measurements, lung volumes will be measured in a body plethysmograph (MedGraphics, St. Paul, MN) with the subjects in a seated position with a nose clip. Subjects will be instructed to pant against the closed shutter at a frequency of 1-3 Hz. Lung volume measurements will be obtained prior to inital chest CT. Subjects will undergo high resolution computed tomography (HRCT) scanning within 30 minutes of initial lung volume measurements.

After the initial HRCT of the chest, subjects will inhale a dose of nebulized ipratropium bromide (0.5 mg) by standard nebulizer after which spirometry and lung volume measurements will be repeated in the pulmonary function laboratory. Spirometry and lung volume measurements will be performed in the same manner. Lung volume measurements will be obtained to account for changes in lung volumes after bronchodilator administration. Changes in lung volumes will be used to account for any changes noted on HRCT scans.

HRCT scanning will begin 6 cm above the top of the dome of the diaphragm, at TLC and moved caudally. Images will be reconstructed with the use of a high-spatial frequency (resolution) algorithm that enhanced edge detection, at a window level of -450 Hounsfield units and a window width of 1,350 Hounsfield units. We will consider the airway diameters after maximum bronchodilation with ipratropium to be a function principally of the structural characteristics of airways. The TLC measurements after ipratropium will be the best reflection of intrinsic structure. CT airway measurement analysis will be performed by VIDA Diagnostics. We have entered into a collaboration with VIDA Diagnostics that will allow accurate and reliable CT airway measurements. Subject's CT images obtained at UTMB will be deidentified and electronically transmitted to a research collaborator at VIDA Diagnostics located in Coralville, IA. The CT images will have a code assigned, known only to the PI. Using a proprietary software platform, airway measurements will be performed and the data electronically transmitted to the PI at UTMB.

Inclusion criteria

• lung transplant recipients >18 years of age
• at least 12 months or greater from time of transplantation

Exclusion criteria

• hemodynamic instability
• hypoxemia
• pneumonia
• moderate or large pleural effusion
• clinical evidence of acute rejection