Use of negative pressure ventilators peaked in the 1950s with the polio_epidemic. Negative pressure ventilators, or body ventilators, operated on the principle of increasing lung volumes by intermittently applying negative pressure to the entire body below the neck or just to the upper region of the chest. The negative pressure was transmitted across the chest wall, into the pleural space, and into the intraalveolar space. The resulting increase in transpulmonary pressure caused air to enter the lungs. Exhalation was simply passive and depended on the elastic recoil of the lung and chest wall.

 

The first successful negative pressure ventilator, known as the iron lung, was designed in 1928 by engineer Phillip Drinker and Dr. Charles McKhann. It consisted of a large, metal cylinder that enclosed the patient's entire body below the neck, leaving the head protruding through an airtight rubber neck seal. A simpler and less expensive version of this tank device, developed by J .H. Emerson in 1931, became the ventilator that was predominantly used to treat people paralyzed by polio. The chest cuirass, or shell ventilator are other negative pressure ventilators.