Analysis of Airstream Inside the Slip Joint of Tracheal Intubation Tube for Breathing Measurement

In a previous study, a flexible thermal flow sensor for detecting respiratory airflow was installed inside the slip joint of an intubation tube system to support its insertion. In this study, the airflow stream distribution in the slip joint is systematically analyzed to determine the optimal placement of the airflow sensor. First, the airflow distribution in both the baby and adult tracheal intubation tubes was analyzed using finite element simulations. Backward flow was discovered near the inside surface of the slip joint during exhalation, with a stronger magnitude in the baby intubation tube in comparison with its adult counterpart. However, no backward flow was observed during inhalation. To clarify the simulated flow profile, the airflow stream inside the slip joint of the baby tracheal intubation tube during exhalation was examined experimentally. A stick-type airflow sensor was proposed and developed using MEMS technology for airflow measurements. The backward airflow was experimentally verified in the vicinity of the inside surface of the slip joint during exhalation, which was in agreement with the simulation results. Consequently, the airflow sensor is found to be optimal when placed around the radial center of the slip joint, which shows a consistent airflow profile under both inhalation and exhalation.