DYNAMIC MEASUREMENT OF TRACHEAL DIAMETER IN DOGS

We describe and validate a new minimally invasive method for continuou s measurement of tracheal diameter in anesthetized dogs. The method is based on measuring displacement of water into and out of a modified e ndotracheal tube cuff placed in the trachea. The system was calibrated to allow tracheal diameter to be calculated from known cuff volume. T he resolution of the method in measuring changes in tracheal diameter is 0.1 mm over a range of similar to 10-25 mm. The apparatus was teste d in five dogs by observing the response of the trachea to four stimul i previously shown to alter tracheal tone: stimulation of nasal mucosa , hyperinflation of the lungs, induction of hypocapnea, and infusion o f atropine. The observed changes in tracheal diameter were generally c onsistent with those of previous studies. The direction and extent of changes in tracheal diameter in response to the test conditions were c onfirmed by fluoroscopy. We conclude that continuous measurement of vo lume changes in the cuff reflects corresponding changes in tracheal di ameter.