This study is a prospective physiologic study. The primary study population will be adult invasive tracheal intubated patients with COPD, and investigators will collect relevant demographic data, vital signs, and baseline physiologic parameters of the patients prior to the spontaneous breathing test（SBT).

The participants will be divided into a successful withdrawal group and a failed withdrawal group according to the SBT outcome, and the changes in the above parameters during SBT will be compared between the two groups .

This observational study mainly include participants who had invasive mechanical ventilation for ≥48 h and are assessed to be ready for the SBT trial.The SBT approach is based on the low-level pressure support mode.

Prior to the SBT trial, baseline demographic and physiologic data of the participants will be collected, and the participants will be divided into two groups based on the results of the SBT trial: successful and unsuccessful, and the physiologic changes during the SBT trial will be compared between the two groups, respectively.

Inclusion Criteria:

• Invasive mechanical ventilation for at least 48 hours

Exclusion Criteria:

• neuromuscular disease；Postoperative patients or patients with traumatic brain injury

Patients undergoing weaning from mechanical ventilation；Hemodynamic stability