An iron lung is a large machine that enables a person to breathe when normal muscle control has been lost or the work of breathing exceeds the person's ability. It is a form of medical ventilator. Properly, it is called a negative pressure ventilator.
In 1931, inveterate tinkerer John Haven "Jack" Emerson unveiled a less expensive iron lung. Drinker and Harvard promptly sued Emerson for patent violations, which proved unwise. In the subsequent legal battles Emerson demonstrated that every aspect of Drinker's patents had been patented by others at earlier times. Emerson won the case, and Drinker's patents were declared invalid.
Entire hospital wards were filled with rows of iron lungs at the height of the polio outbreaks of the 1940s and 50s. With the success of the worldwide polio vaccination programs which have virtually eradicated new cases of the disease, and the advent of modern ventilators that control breathing via the direct intubation of the airway, the use of the iron lung has sharply declined.
The iron lung now has a marginal place in modern respiratory therapy. Most patients with paralysis of the breathing muscles use modern mechanical ventilators that push air into the airway with positive pressure. These are generally efficacious and have the advantage of not restricting patients' movements or caregivers' ability to examine the patients as significantly as an iron lung does. However, negative pressure ventilation is a truer approximation of normal physiological breathing and results in more normal distribution of air in the lungs. It may also be preferable in certain rare conditions, such as Ondine's curse, in which failure of the medullary respiratory centers at the base of the brain result in patients having no autonomic control of breathing. At least one reported polio patient had a spinal deformity that caused the use of mechanical ventilators to be contraindicated. Thus, there are patients who today still use the older machines, often in their homes, despite the occasional difficulty of finding the various replacement parts. Joan Headley of Post-Polio Health International stated to CNN that there are approximately 30 patients in the USA still using an iron lung
The iron lung was shown in a short scene in the film The Big Lebowski in full use.