The iron lung, officially known as a tank respirator, is a large, horizontal, airtight cylinder designed to provide mechanical breathing assistance. Invented in the late 1920s, this device represented a breakthrough in life support technology. It became one of the most recognizable medical machines of the 20th century, offering survival for patients whose ability to breathe had been lost. Its creation was a direct response to a public health crisis that demanded an immediate mechanical solution.
The Medical Crisis: Respiratory Paralysis from Polio
The necessity for the iron lung stemmed from the devastating effects of poliomyelitis, a viral infection that reached epidemic proportions in the early 1900s. While most infections caused mild or no symptoms, a small percentage progressed to the paralytic form. The poliovirus specifically targets and destroys motor neurons within the central nervous system, which control muscle movement.
The most severe form, known as bulbospinal polio, involved the destruction of motor neurons in the spinal cord and the brain stem. This led to the paralysis of the muscles responsible for breathing, primarily the diaphragm and the intercostal muscles. Patients afflicted with this condition, often conscious and alert, suddenly became unable to draw a single breath.
Before the invention of the tank respirator, there were no effective methods for prolonged mechanical ventilation for these patients. Treatments like manual resuscitation were temporary at best, and fatality rates reached 80 to 90 percent for those with acute respiratory paralysis. A device was required to keep the respiratory system functioning until the patient could potentially recover.
Designing the Solution: Mechanics of Negative Pressure Ventilation
The solution was first developed in 1928 by industrial hygienist Philip Drinker and physiologist Louis Agassiz Shaw at Harvard University. Their invention, the Drinker respirator, was a large metal box operating on the principle of external negative pressure ventilation. This mechanism was designed to mimic the natural process of breathing.
Normal inhalation occurs when the diaphragm contracts, expanding the chest cavity and creating negative pressure inside the lungs. This pressure difference causes air to rush in. The iron lung replicated this physiological process externally, forcing the body to breathe by manipulating the air pressure surrounding the patient.
When a patient was sealed inside the chamber, a motorized pump mechanism began its rhythmic work. The pump periodically drew air out of the sealed tank, creating negative pressure around the patient’s chest and abdomen. This drop in external pressure forced the lungs to expand, pulling in air through the mouth and nose.
The pump would then reverse, allowing air back into the chamber to equalize the pressure, causing the patient to exhale passively. This regulated cycle provided the necessary rhythm of respiration. The initial Drinker model was soon improved upon by John Haven Emerson, whose design was lighter, quieter, and included access ports for patient care.
Peak Use and Transition to Modern Respiratory Care
The iron lung became a common sight in hospital wards across the world during the height of the polio epidemics in the 1940s and 1950s. At its peak, thousands of individuals relied on these devices to survive the acute phase of the disease or for long-term support. The sight of entire rooms filled with the cylindrical machines, each with a patient’s head protruding from the collar, symbolized the widespread impact of the infectious disease.
The widespread deployment of the iron lung began to decline sharply due to two major medical advancements. The first was the successful development and mass distribution of the polio vaccines: the inactivated Salk vaccine (1955) and the oral Sabin vaccine (1961). These vaccines dramatically reduced the incidence of poliomyelitis, eliminating the primary cause of respiratory paralysis.
The second factor was the simultaneous emergence of more advanced respiratory support technology, particularly the positive pressure ventilator. Unlike the iron lung, which pulls air into the lungs, positive pressure ventilators work by pushing air directly into the airway, often through a tube inserted into the windpipe (tracheostomy). This new approach, pioneered during a polio outbreak in Copenhagen in 1952, allowed for better management of secretions and was more effective for patients with complex bulbar polio symptoms. Positive pressure technology also led to the creation of smaller, more portable, and less invasive devices, ultimately rendering the massive tank respirator obsolete for standard medical care.