RESULTS: With increasing saline: (1) The trigger time: TItri (Pmask), TItri (Ppro) and TItri (Pdis) increased (from 0.093±0.053 to 0.278±0.120s, from 0.108±0.056 to 0.255±0.129s, and from 0.094±0.048 to 0.212±0.117s respectively). The trigger pressure TPtri (Pmask), TPtri (Pro) and TPtri (Pdis) increased (from 0.269±0.216 to 2.730±1.548cm H2O, from 0.284±0.227 to 2.679±1.529cm H2O and from 0.274±0.214 to 2.573±1.994 cm H2O respectively). The pressure-time product (PTP) increased (from 0.031±0.038 to 0.717±0.842 cm H2O*S, from 0.038±0.045 to 0.747±0.908cm H2O*S, and from 0.031±0.039 to 0.467±0.262cm H2O*S respectively). (2) Ineffective triggering rate increased from 0to8 times/min; Spurious triggering rate from 0 to 33 times/min. (3) The plateau pressure of Pmask and Ppro is exceed preset parameter, increased significantly compare with 0ml, from 10.108±0.207 to 17.744±1.915cm H2O and from 10.115±0.220 to 17.72±1.947cm H2O. The chang of plateau pressure of Pdis is not significantly (from 10.169±0.193 to 10.858±0.351cm H2O). The baseline pressure of Pmask, Ppro and Pdis changed from 3.902±0.299 to 10.454±1.893cm H2O, from 3.897±0.307 to 10.465±1.866 cm H2O and from 3.919±0.146 to 4.475±1.063cm H2O respectively. (4) The pressure fluctuation of platform and baseline indicated the pressure support is instability. (5) The time when the pressure of the Pdis began to change was delayed to Pmask and Ppro, delayed 0.099±0.087S comparaed with 0 ml.