The iron lung, formally known as the negative pressure ventilator or tank respirator, stands as a powerful symbol of 20th-century medicine. Invented in 1927 by Philip Drinker and Louis Agassiz Shaw at Harvard, this machine became the primary method of life support for thousands during the devastating Polio epidemics. While its use is rare today, the device provided a solution for patients who had lost the ability to breathe on their own. This large, cylindrical apparatus bridged the gap between respiratory failure and survival for those afflicted by paralyzing illnesses.
How the Machine Mimics Natural Breathing
The iron lung operates on the principle of negative pressure ventilation, a method that closely mirrors the body’s natural breathing mechanism. When a person inhales normally, the diaphragm contracts and the rib cage expands, creating a negative pressure, or slight vacuum, inside the chest cavity that draws air into the lungs. The tank respirator simply externalizes this process.
The patient is sealed inside the airtight metal cylinder with a rubber gasket around the neck, leaving only the head exposed to the ambient air. An electric motor powers a pump or bellows that cyclically lowers the air pressure inside the tank. This drop in pressure forces the chest wall and diaphragm to rise, pulling air into the lungs through the patient’s nose and mouth.
When the pump reverses or the pressure is allowed to equalize with the outside atmosphere, the elasticity of the chest and lungs naturally pushes the air out, resulting in exhalation. This rhythmic alternation of pressure creates a continuous cycle of artificial respiration, sustaining life for those whose own muscles are paralyzed. The process is non-invasive, which was a significant advantage for long-term use.
The Polio Crisis and Respiratory Paralysis
The iron lung gained prominence due to the massive scale of the Poliomyelitis outbreaks that swept through developed nations, particularly in the 1940s and 1950s. The Polio virus, an enterovirus, typically caused mild, flu-like symptoms, but in approximately one percent of cases, it invaded the central nervous system. This invasion often led to paralytic polio, where the virus destroyed the motor neurons in the spinal cord.
The most feared manifestation was bulbar polio, which targeted the brain stem, or the “bulb,” a region controlling automatic functions like breathing and swallowing. When the virus attacked the motor neurons of the phrenic nerve, it caused paralysis of the diaphragm and other respiratory muscles, making it impossible for the patient to inhale. Without mechanical assistance, death from suffocation was inevitable within hours.
During the epidemic peaks, entire hospital wards were filled with rows of these respirators, as they were the only technology available to sustain life for the severely paralyzed. Patients who entered an iron lung faced dire odds, as some outbreaks saw mortality rates as high as 70% for those requiring respiratory support. For those who survived the acute phase, the device served as a lifeline, buying time for the body to potentially recover partial muscle function.
Daily Life and Long-Term Care for Iron Lung Users
For patients requiring long-term care, life inside the metal tank presented immense physical and psychological challenges. The design meant the patient was fully encased, complicating daily living and medical care. Nurses and doctors had to utilize air-sealed portholes, often equipped with long gloves, to reach inside the tank and perform necessary tasks like administering medicine or adjusting linens.
To facilitate communication and reduce isolation, mirrors were often positioned above the patient’s head, allowing them to see the room and interact with visitors and caregivers. For hygiene, the patient could sometimes be briefly wheeled out of the machine on a sliding bed, a process that required holding their breath or receiving temporary manual ventilation. This brief window outside the tank was stressful, as the patient’s life depended on the swiftness of the care team.
Many patients learned to adapt to this confined existence, developing techniques like “frog breathing” (glossopharyngeal breathing) to take in sips of air and spend short periods out of the iron lung. The burden of constant dependency on the rhythmic “whoosh” of the machine was profound, yet some long-term users managed to pursue education, careers, and a degree of independent living. These individuals often formed deep bonds with the device, describing it as a natural extension of their own body’s breathing process.
The Shift to Modern Ventilatory Support
The primary reason for the iron lung’s obsolescence was the development and widespread distribution of the Polio vaccine. The introduction of the Salk injectable vaccine in 1955 and the Sabin oral vaccine soon after led to a dramatic and nearly complete eradication of wild poliovirus in industrialized nations. With new cases of paralytic polio virtually disappearing, the demand for the tank respirator vanished.
Simultaneously, medical technology shifted toward a fundamentally different mechanism for respiratory assistance: positive pressure ventilation (PPV). Modern ventilators work by actively pushing air into the lungs through a tube inserted into the trachea or via a non-invasive mask. This approach proved more portable, versatile, and allowed for much easier patient access for nursing and medical procedures.
While PPV became the new standard of care, it can carry risks, such as lung injury from high pressure. This is why the less invasive negative pressure approach is still considered more physiological. Today, the iron lung is rarely used, but a few long-term survivors of the Polio epidemic continue to rely on their well-maintained machines, finding the rhythmic, external pressure more comfortable and effective than modern alternatives.