Pressure Support Ventilation use Expiratory triggering sensitivity (Esense) to transfer inspiration to expiration, the value of Esense is fixed. That may lead to asynchrony between humans and ventilators, making people uncomfortable and prolonging weaning time. Furthermore，trigger delay or inffective trigger happens frequently during insppiratory triggering. The ventilators have a compunter drived funcation of automatic adjustmen of inspiratory triger and cycling-off based on waveform, IntelliCycleTM 2.0. It will make the transforming more synchrony with humans. The objectibe of the present study is to detect the effect of automatic adjustmen of inspiratory triger and cycling-off based on waveform on patient-ventilator interation.

This is a physiological cross-over study. Enrolled patient with different baseline respiratory mechanics, for example ARDS patients with low compliance, COPD patient with high airway resistance and postoperative patients with almost normal compliance and airway resistance. Patients are ventilated with PSV+ Automatic adjustmen of inspiratory triger and cycling-off based on waveform, PSV with fixed inspiratory and expiratory and NAVA in two different levels of support. The demographic characteristics, diagnosis, formerly medical history, Ventilator indications, Ventilator data, other respiratory treatments, patient-ventilator interation, work of breathing, Eadi, will be recorded.

Inclusion Criteria:

Postoperation patients

1. receiving invasive mechanical ventilation due to operation
2. abdominal surgery, orthopedic surgery or gynecological surgery
3. without respiratory system Comorbidity
4. able to sustain PSV more than 1 h with inspiratory support ≤ 15 cmH2O.

COPD and ARDS patients

1. receiving invasive mechanical ventilation due to acute respiratory failure
2. able to sustain PSV more than 1 h with inspiratory support ≤ 15 cmH2O.

Exclusion Criteria:

1. age < 18 or >85 years,
2. tracheostomy at time of inclusion,
3. contra-indication for nasogastric tube insertion (e.g. history of esophageal varices, gastro-esophageal surgery in the previous 12 months or gastro-esophageal bleeding in the previous 7 days, INR ratio > 1.5 , APTT > 44 s, history of leukemia),
4. neuromuscular disease affecting spontaneous breathing (e.g. history of acute central or peripheral nervous system disorder or neuromuscular disease with irregular spontaneous rhythm),
5. hemodynamic unstable (heart rate > 140 beats/min, vasopressors required with ≥ 5 μg.kg-1.min-1 dopamine/ dobutamine, or ≥ 0.2 μg.kg-1.min-1 norepinephrine),
6. sedation level Richmond Agitation-Sedation Scale (RASS) ≤ -2 or ≥ 2,
7. lack of informed consent and patients included in other intervention study.