HRCT imaging of airway responsiveness: Effects of anesthetics

The noninvasive imaging method, high resolution computed tomography (HRCT), has been developed in animal models and applied to humans with obstructive lung disease for assessing regional and individual airway responsiveness. The ability to directly view airway responses during provocations such as t racheal intubation in an asthmatic could greatly enhance our understanding and treatment of airway hyperresponsiveness. HRCT uses increased kilovoltag e peak (kVp) and milliamperage (mAs) settings, thin slices, high spacial fr equency reconstruction algorithms, and small fields of view to resolve stru ctures as small as 200 mum. Therefore, airways as small as 1-2 mm in diamet er can be viewed and measured. HRCT is a more sensitive technique for resol ving airway caliber changes than clinical or research methods of pulmonary function tests. HRCT allows direct in vivo measurement of airway responsive ness to pharmacological and physiological stress that induces bronchoconstr iction or bronchodilation. Using HRCT, we are able to measure airway dilati on at baseline airway tone with inhalation anesthetics, differentiate the b ronchodilating properties of inhalational agents in airways with tone, asse ss bronchodilating agents commonly used as premedications prior to anesthes ia, and measure airway heterogeneity at baseline tone and their response to a variety of stimuli. This ability of HRCT to measure airway caliber and r esponse heterogeneity in vivo noninvasively will dramatically improve our u nderstanding of pulmonary physiology in general and the effects of anesthet ics on the airways specifically.