Model of a New Generation of Tracheostomy and Endotracheal Tubes

The feasibility of monitoring cannula obstruction was studied by conversion of the electrical resistance of substances that are capable of causing obstruction into audible auditory signals. Copper-nickel-gold electrodes were thermal pressed onto polyimide-based flexible films placed as 1-mm wide strips along the inner surface of tracheostomy and endotracheal tubes. The responses were fed into a resistance-to-frequency converter (IC 555 timer), and the output was frequency selected to generate auditory responses through a piezoelectric beeper. Quantitative estimates of responses from the IC output were computer averaged. Instantaneous obstruction detection was made possible by the immediate responsiveness of the device in the presence of obstruction.