[Effect of connecting airbag in different filling state at the front end of piezometric tube in noninvasive ventilation circuit on man-machine synchronization]

Objective: To investigate the effect of connecting airbag in different filling state at the front end of piezometric tube in the noninvasive ventilation circuit on pressure transmission and human-machine synchronization. Method: In test 1, the airbag was connected to a piezometric tube which was placed in a closed container, the filling state of the airbag was regulated, and the pressure inside the container was changed to observe the corresponding pressure change in the piezometric tube. In test 2, the airbag in different filling state was connected at the front end of piezometric tube in noninvasive ventilation circuit. Twelve subjects were connected to the ventilator such that dynamic changes in the pressure inside the mask (Pmask) and piezometric tube (Ptube) could be measured. Data with normal distribution was analyzed by t test, while data with abnormal distribution was analyzed by K-W test. Results: In test 1, the pressure inside the container changed between 0 and 50 cmH(2)O(1 cmH(2)O=0.098 kPa), when the big airbag was filled at 1/5, 2/5, 3/5, 4/5, the medium-sized airbag was filled at 3/5, 4/5, 5/5, and the small airbag was filled at 4/5, the pressure inside the piezometric tube changed synchronously with the pressure inside the container with no statistically significant difference(P>0.05). In a state of no filling in the small airbag and the medium-sized airbag, and filled at 1/5 in the small airbag, the pressure inside the piezometric tube no longer changed with the pressure in the container when the pressure reached a certain level .When the small airbag was filled at 1/5, 2/5, 3/5, 5/5, the medium-sized airbag at 1/5, 2/5, and the big airbag at 5/5, and all the airbags were in the state of no filling , the difference in the pressure between the piezometric tube and the container was statistically significant. In test 2, respiratory ventilation parameters were set on 10/4 cmH(2)O-30/14 cmH(2)O , and the connecting airbag at the front end of piezometric tube in noninvasive ventilation circuit. The platform pressure in the mask was slightly higher than that in the piezometer tube, and the baseline pressure in the mask was slightly lower than that of the piezometer tube. When the big airbag was filled at 1/5, 2/5, 3/5, 4/5 and medium-sized airbag at 2/5, 3/5, 4/5, the pressure difference between Pmask and Ptube was less than 0.5 cmH(2)O, which was acceptable clinically. When the big airbag was filled at 1/5, 2/5, 3/5 and the medium-sized airbag at 2/5, 3/5, there was no significant difference in trigger work before and after connecting the airbag at the front end of the piezometric tube(P>0.05). Conclusion: Connecting the airbag at the front end of the piezometric tube could avoid the forming of condensate in piezometric tube. The airbag showed good properties of pressure conductivity under ideal size and filling state.