Effect of a Waterproof Device in the Noninvasive Ventilation Circuit on patient-machine Synchronization

Objective: Investigate the effect of connecting a waterproof device at the front end of the piezometric tube on pressure transmission and patient-machine synchronization during the noninvasive ventilation. Method: In test 1, the waterproof device was connected to the piezometric tube and put into a closed container, the pressure inside the container was varied to observe the corresponding pressure change in the piezometric tube. In test 2, a waterproof device was connected in front of the piezometric tube during noninvasive ventilation.12 subjects were received noninvasive ventilator so that dynamic changes of the pressure inside the mask (Pmask) and piezometric tube (Ptube) could be measured. Results: In test 1, when the pressure in the container was gradually increased to 50 cmH2O and then decreased to 0, the pressure inside the piezometric tube changed synchronously with the pressure inside the container, with no statistically significant difference between the pressures (0.009 ± 0.138) cmH2O. In test 2, there was no significant increase in triggering time, pressure, and power after connecting the waterproof device at the front end of the piezometric tube. There was no significant difference in the platform pressure and baseline pressure as measured by Pmask, before and after connecting the waterproof device. Finally, there was no significant difference in the platform pressure and baseline pressure between Pmask and Ptube after connecting the waterproof device. Conclusion: Connecting the waterproof device at the front end of the piezometric tube can prevent condensate from entering the tube without affecting pressure transmission . DOI : COMING SOON Corresponding author: Zheng Zeguang , First Affiliated Hospital of Guangzhou Medical University (State Key Laboratory of Respiratory Disease), Guangzhou Institute of Respiratory Disease, Guangzhou, Guangdong 510120, China


Introduction
Noninvasive positive pressure ventilation (NPPV) has been widely used in clinical and family rehabilitation. Since being developed, noninvasive ventilation has played an important role in treating acute and chronic respiratory failure [1][2][3][4] . Compared with invasive mechanical ventilation, it has the advantage of being implemented at any time according to the requirements of the disease. In addition, ventilator-associated pneumonia and other serious complications are significantly reduced. [5,6] However, poor patient-machine synchronization is one of the major reasons why patients are reluctant to undergo noninvasive ventilation [7,8] , which affects clinical application of the technique. There are many factors that affect patient-machine synchronization, but the factors with clinical significance are patient factors, ventilator performance, respiratory parameters, ventilation mode, and leakage [9][10][11] .
However, in clinical practice, patient-machine asyn-

Results
Test 1: The pressure difference between the piezometric tube and the container was (0.009 ± 0.138) cmH 2 O, and there was no significant difference between the two (P> 0.01) (Fig. 5).   (Table 1).
(2)There were no significant statistical differences in platform and baseline pressures measured via the mask, before and after connecting the waterproof valve at the front end of the piezometric tube (Table 1).
(3)There were no significant statistical differences in platform and baseline pressures between Pmask and Ptube , after connecting the waterproof valve at the front end of the piezometric tube (Table 1).

Discussions
In the over 10 years of development, The patient-machine synchronization of noninvasive ventilation is mainly manifested in three aspects: inspiratory trigger, pressure support level and inspiratory-expiratory switching [13,14] , which is realized through a piezometric tube in the noninvasive  prolonged triggering, increased triggering pressure, enhanced triggering powers and unstable gas supply [15] .
Therefore, we developed a waterproof device that connected at the front end of piezometric tube which is made of waterproof breathable membrane, and the membrane part is a hydrophobic material. It can prevent the condensate from entering piezometric tube without obstructing conduction of pressure.
From the results of test 1, we see that the pressure change is always consistent between piezometric tube and inside container after a waterproof device is connected at the front end of piezometric tube, and comparison between the two is not statistically significant (Fig. 5). The results of Test 2 show that in noninvasive ventilation, the pressure of Ptube and Pmask always remains synchronized changing at different pressure support levels (the inspiratory pressure increased from 10cmH 2 O to 30cmH 2 O, and the expiratory pressure increased from 4cmH 2 O to 14cmH 2 O), with a waterproof device connected at the front end of piezometric tube. With a waterproof device connected at the front end of piezometric tube, the ventilator's gas supply is stable .There is no significant difference in Pmask with a waterproof device connected at the front end of piezometric tube comparing that situation with no waterproof device, and there is no significant difference in the triggering time, pressure and power.

In summary
In this study connecting a waterproof device at the front end of piezometric tube can prevent condensate from entering piezometric tube, which does not affect the pressure conduction and patient-machine synchronization of noninvasive ventilation.