you can see the large airways in silhouette because the smaller airways are full of fluid and inflammatory cells. The 1918 patients were described as drowning and that is why. It is impossible to ventilate this patient because the lungs are so stiff. We use ECMO - an artificial heart and lung which is inserted for 2 weeks to keep the patient alive while the lungs recover. In influenza of this sort the illness goes from 0-60 in a few days then gets better within a week. We remove the machine and over 80% of young people survive.
There is much more air in the lungs than the severe flu patient. However the gas exchange deficit is just as bad and the lungs are also unexpectedly stiff. We think in many patients there is not just inflammation in the airway but that the pulmonary arteries are also full of clot because of the hyper coagulation state which is also taking out the heart, brain and kidneys in some patients. Unlike the flu these patients are taking weeks to recover and then for many the lungs seem irretrievably scarred.
I remember seeing one patient with similar lung physiology and that turned out to be cancer in the smallest lung blodd vessels. I don't remember seeing this due to infection but if it happened ince a year and i wasn't on the ward that week then i wouldn't see it.