The tank respirator, commonly known as the iron lung, is a historical medical device designed for prolonged respiratory support. This large, horizontal metal cylinder acts as a mechanical respirator by completely enclosing a patient’s body up to the neck. It provided a means of respiration for individuals who had lost the ability to breathe on their own. The device became a recognized symbol of a public health crisis in the mid-20th century, though its use extended beyond that singular disease.
The Immediate Need for Assisted Breathing
The necessity for a machine like the iron lung was driven by poliomyelitis, or polio, a viral infection that reached epidemic proportions. The poliovirus invades the nervous system, causing paralysis by destroying nerve cells that control muscle movement. In severe cases, the virus affected the motor neurons responsible for respiration.
A specific concern was bulbospinal polio, which paralyzed key breathing muscles, particularly the diaphragm and the intercostal muscles. Without the ability to contract these muscles, patients suffered respiratory failure. Before the iron lung, doctors had few options for long-term, continuous respiratory support, resulting in a high mortality rate. The technology was needed to mechanically perform the work of breathing until the patient recovered the use of their own muscles.
The Genesis of the Iron Lung
The iron lung was first developed in 1928, providing the first solution to the problem of respiratory paralysis. The machine was the creation of two Harvard University researchers: industrial hygienist Philip Drinker and physiologist Louis Agassiz Shaw. Their initial model, known as the Drinker respirator, made its clinical debut at Boston Children’s Hospital that same year.
The device was enormous, often weighing over 1,000 pounds and resembling a large metal tank. It was also expensive, costing around $1,500 in 1939, which limited its availability. Despite its bulk, it was immediately hailed as life-saving technology, initially used for victims of coal gas poisoning before becoming synonymous with the polio epidemic. John Haven Emerson improved the design in 1931, creating a lighter, more reliable, and more affordable version that became the standard in hospitals.
How the Tank Respirator Provided Life Support
The tank respirator operated on the principle of negative pressure ventilation, a method that mechanically mimics the body’s natural breathing process. When a person breathes normally, the diaphragm contracts, lowering the pressure inside the chest cavity to draw air in. The iron lung created this pressure change externally.
The patient’s body was sealed inside the airtight chamber, with only their head protruding through a rubber collar. A motor-driven pump lowered the air pressure inside the tank, creating a slight vacuum around the body. This reduction in pressure forced the chest wall to expand, drawing air into the lungs through the nose and mouth.
The pump then quickly normalized the pressure, allowing the chest and lungs to recoil passively, pushing the air out in a simulated exhalation. This rhythmic cycling kept the patient breathing as long as their respiratory muscles remained paralyzed. The process required the patient to remain immobile inside the bulky cylinder for extended periods, sometimes for years or even decades.
The Iron Lung’s Decline and Replacement
The primary reason for the iron lung’s obsolescence was the Polio vaccine. The widespread use of the Salk vaccine, introduced in 1955, and the later Sabin oral vaccine reduced the number of new polio cases. As the incidence of poliomyelitis declined, the need for mass-produced tank respirators vanished.
Technological advancements also played a significant role in the iron lung’s decline. Beginning in the 1950s, positive-pressure ventilators were developed, which forced air directly into the patient’s lungs through a tube inserted into the airway. These newer machines were smaller, less expensive, and provided better access to the patient for nursing care and medical procedures. The compact, versatile positive-pressure ventilators ultimately replaced the cumbersome iron lung as the preferred method for long-term and acute respiratory support.