ASA 127th Meeting M.I.T. 1994 June 6-10

4pEA9. Determination of breathing tube position and patency using acoustic reflectometry.

Jeffrey P. Mansfield

George R. Wodicka

School of Elec. Eng., Purdue Univ., West Lafayette, IN 47907-1285

A new technique for determining the position and patency of tubes placed within the body using acoustic reflectometry was developed. The technique was used to guide and monitor endotracheal tubes (ETT) in four canines requiring breathing assistance during surgery. An incident sound pulse, generated by a small speaker in a tube, was injected into the proximal end of the ETT. The pulse then traveled down the ETT, was emitted into the airways, and the resulting reflections were measured by a microphone as they propagated back up the tube toward the speaker. A characteristic inverted reflection from the airways was measured and its timing was used to determine ETT position or movement. In addition, the reflection from the distal end of the ETT was used to estimate the diameter of the intubated airway. The location and degree of obstruction in the ETT was also estimated. The information provided by the device insured proper tracheal placement, patency, and accurate detection of ETT movement. [Work supported by NSF.]