“Most people used the iron lung for a few weeks or months depending on the intensity of the polio attack. However, those with chest muscles permanently paralyzed by the disease need it for their lifetime.”

I am not any kind of medical professional so I can’t personally vouch for it, but here’s where I got the quote

https://www.medicinenet.com/how_long_can_you_live_in_an_iron_lung/article.htm