Inclusion Criteria:

• Age: Age ≥ 18 years.
• Mechanical Ventilation Duration: Receiving invasive mechanical ventilation for ≥ 24 hours.
• Weaning Readiness: The attending physician has determined that the patient meets the criteria for weaning assessment and plans to conduct a Spontaneous Breathing Trial (SBT) under Pressure Support Ventilation (PSV) mode.
• Hemodynamic Stability: Hemodynamically stable prior to the SBT, defined as a mean arterial pressure (MAP) ≥ 65 mmHg, or requiring only low-dose vasopressor support.
• Oxygenation Criteria: Oxygenation status permits an SBT, typically defined as FiO2 ≤ 0.60 and PEEP ≤ 10 cmH2O, or meeting the standard weaning assessment criteria of the participating institution.

Exclusion Criteria:

• Known or highly suspected phrenic nerve injury, or unilateral/bilateral diaphragmatic paralysis.
• Neuromuscular diseases causing severely restricted spontaneous breathing capacity, as judged by the investigator to be unsuitable for RDSI analysis.
• Recent chest or upper abdominal surgery, open trauma, skin infection, or extensive dressing coverage that prevents obtaining a reliable diaphragm ultrasound window.
• Significant agitation or severe patient-ventilator asynchrony that prevents the acquisition of continuous and stable respiratory cycles.
• Undrained pneumothorax, or conditions deemed unsuitable for ultrasound examination as judged by the attending physician.
• Pregnant patients.
• The patient or their legally authorized representative refuses to participate in the study.