As doctors treat more patients who are severely ill from COVID-19, they’re noticing differences in how their lungs are damaged. Some patients coming to the hospital have very low oxygen levels in their blood, but you wouldn’t necessarily know it from talking to them. They don’t seem starved of oxygen. They may be a little confused. But they aren’t struggling to breathe. When doctors take pictures of their lungs -- either with a CT scanner or an X-ray machine -- those also look fairly healthy. The lungs may have a few areas of cloudiness and crazing, indicating spots of damage...