Test procedure
CAVITY
Before the test, all participants were given an explanation of the test procedure to ensure their understanding. The participants rested for 10 minutes before the start of the experiment to achieve a physiological steady state. During the study, the participant calmly sat in a vertical position with their mouth closed breathing through their nose (oxygen concentration of inhaled gas 21%, temperature 36 °C, and relative humidity 100%). A handheld digital manometer (AZ8252; AZ Instrument Corp., Taiwan, China) was used to measure the EEP and end-inspiratory pressure (EIP). One end of an anesthetic catheter (Henan Tuoren Medical Device Co., Ltd., Xinxiang, Henan, China) was inserted into the nasal cavity to a depth of 4 cm, and the other end was connected to the handheld digital manometer through the adapter. A previous study showed that the pressure does not increase at a nasal depth beyond 3 cm [Flowchart