USING ACOUSTIC REFLECTOMETRY TO DETERMINE BREATHING TUBE POSITION ANDPATENCY

A new technique to guide and determine the patency of tubes placed wit hin the human body was developed using the principles of time domain a coustic reflectometry. An audible sound pulse is introduced into the p roximal end of the tube or catheter and the sonic reflections from the tube lumen and body cavity are analyzed to provide patency and positi on information, respectively. The information can be used to initially place the tube and monitor its position and patency thereafter. A ded icated instrument was developed for use with breathing tubes, known as endotracheal tubes (ETT), that are necessary for the mechanical venti lation of patients. The incident sound pulse is generated and it is me asured along with the resulting reflections in a small wave tube conne cted to the ETT. When the ETT is properly placed in the trachea below the vocal folds, a characteristic reflection from the airways is measu red and the timing between the incident pulse and this reflection is u sed to determine ETT position or movement. The reflection from the dis continuity between the distal ETT tip and the airway is used to estima te the diameter of the airway at this point. In addition, reflections from the ETT lumen are used to generate a profile of the lumen area ov er the length of the tube. This information allows reliable differenti ation between proper and erroneous tube placement, quantification of m ovement over time, and provides the location and degree of obstruction s within the lumen. (C) 1995 Academic Press Limited.