very carefully. the nurse spoon-fed them. eating while lying down is uncomfortable but asphyxiating is a lot worse. there are ports on the sides that allowed nurses to reach in and do necessary tasks like washing. patients used a bedpan to go to the bathroom and the nurses cleaned them afterward. it could be opened up completely when necessary but depending on how bad the patient was they would have difficulty breathing or be completely unable to while it was open.
nowadays most people are intubated instead. there are very few iron lungs in use, like in the single digits.
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