What is this study about? This research aims to test a new ultrasound technology called speckle tracking to measure how much the lining of your lungs (pleura) stretches during breathing, especially if you're on a breathing machine (ventilator). Doctors want to see if this technology can help them adjust ventilator settings more safely, reducing the risk of lung damage. Why is this important? Lung protection: Patients on ventilators, especially those with severe lung problems (like ARDS or pneumonia), need careful settings. Too much pressure from the ventilator can harm the lungs. Better monitoring: Current tools can't easily measure lung stretching at the bedside. This ultrasound method might offer a simple, painless way to check lung health in real time. Who can join? Included: Adults (18+ years) in the ICU with serious illness (assessed by a standard score called APACHE II \>8), whether on a ventilator or not. Excluded: People with recent chest surgery, broken ribs, nerve/muscle diseases, or pregnancy (to avoid risks and ensure accurate measurements). What will happen during the study? Ultrasound scans: A small probe will be placed gently on your chest for 5-10 minutes. The machine will record videos of your lung movements during breathing. This is painless and uses no radiation. Measurements: Doctors will repeat the scan twice (10 minutes apart) to check consistency. For ventilator patients, scans will be done at different pressure settings to see how lung stretching changes. How will this help me or others? Direct benefit: You'll receive detailed monitoring of your lung function, which may help doctors personalize your care. Future benefit: If successful, this technology could help doctors worldwide adjust ventilators more safely, reducing complications for ICU patients. Is my information safe? All data (scans, medical records) will be anonymized and stored securely. Participation is voluntary, and you can withdraw anytime without affecting your treatment. Who is conducting the study? Led by Dr. Xu Qiancheng and the ICU team at Yijishan Hospital, Wannan Medical College. Experts in ultrasound and critical care will ensure the study is safe and scientifically rigorous.