Copyright © 2018 American Academy of Pediatrics. From: P Red Book® 2015, 2015 Figure Legend: The physician is shown here examining a tank respirator, also known as an iron lung, during a polio epidemic. The iron lung encased the thoracic cavity externally in an air-tight chamber. The chamber was used to create a negative pressure around the thoracic cavity, thereby causing air to rush into the lungs to equalize intrapulmonary pressure. Courtesy of Centers for Disease Control and Prevention Date of download: 3/6/2018 Copyright © 2018 American Academy of Pediatrics. All rights reserved.