Diaphragmatic Physiology Similarity Index May Titrate HFNC Flow Setting: A Prospective Observational Study

Feasibility and reproducibility：adult ICU patients Methodology for diaphragmatic motion synchrony:healthy adults and adult ICU patients Between-group comparisons and flow-titration study Inclusion Criteria: 1. Age ≥18 years old. 2. Clear diagnosis of respiratory failure requiring respiratory support. 3. Expected duration of respiratory support ≥24 hours or (high-flow/non-invasive ventilation) ≥48 hours. 4. Voluntary participation in this study and signed informed consent. If the participant is unable to read or sign the informed consent form due to incapacity (e.g., unconsciousness), the legal guardian must act as a proxy in the informed consent process and sign the form. If the participant cannot read the consent form (e.g., illiterate participants), a witness must observe the informed consent process and sign the form. Exclusion Criteria: 1. Severe chest wall deformities or diaphragmatic paralysis. 2. End-stage disease with a predicted life expectancy of less than 24 hours. 3. Inability to acquire STE (strains and echoes) images (e.g., severe subcutaneous emphysema, position limitations). 4. Vulnerable groups other than critically ill patients/elderly/illiterate individuals, including those with mental disorders, cognitive impairments, pregnant women, etc.