How does iron lung work

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Last updated: April 8, 2026

Quick Answer: The iron lung is a negative pressure ventilator that treats respiratory paralysis by creating pressure changes around the patient's body. It was invented in 1927 by Philip Drinker and Louis Shaw at Harvard University, with the first successful use on a polio patient occurring in 1928. During the 1940s-1950s polio epidemics, over 1,200 iron lungs were in use in the United States alone. Modern positive pressure ventilators have largely replaced iron lungs, though a few patients still use them today.

Key Facts

Invented in 1927 by Philip Drinker and Louis Shaw at Harvard University
First successfully used on a polio patient in 1928 at Boston Children's Hospital
During peak polio epidemics, over 1,200 iron lungs were in use in the United States
Operates by creating negative pressure (typically -15 to -20 cm H₂O) to expand the chest
Only 2-3 patients worldwide still used iron lungs as of 2023

Overview

The iron lung, formally known as a negative pressure ventilator, emerged as a life-saving medical device during the polio epidemics of the mid-20th century. Poliomyelitis, a viral infection that attacks the nervous system, often caused respiratory paralysis by affecting the muscles that control breathing. Before the development of effective vaccines in the 1950s, polio outbreaks paralyzed thousands of children and adults annually, with the United States experiencing its worst epidemic in 1952 with over 57,000 reported cases. The iron lung represented a critical technological response to this public health crisis, allowing patients with paralyzed respiratory muscles to survive what would otherwise be fatal respiratory failure. These large metal cylinders became iconic symbols of both medical innovation and the terror of polio, filling hospital wards during outbreaks. The device's development marked a significant advancement in respiratory therapy, preceding modern positive pressure ventilators that would eventually replace it.

How It Works

The iron lung operates on the principle of negative pressure ventilation. The patient lies inside a sealed metal cylinder with only their head protruding through a rubber neck seal. A pump mechanism rhythmically decreases and increases the air pressure inside the chamber. When the pump creates negative pressure (typically around -15 to -20 cm H₂O), the pressure inside the cylinder drops below atmospheric pressure, causing the patient's chest to expand. This expansion lowers pressure in the lungs, drawing air in through the nose and mouth—simulating inhalation. When the pump releases the negative pressure, the chest naturally recoils, pushing air out of the lungs in exhalation. This cyclical process continues at a rate matching normal breathing (typically 12-20 cycles per minute). The device effectively replaces the function of paralyzed diaphragm and intercostal muscles by using external pressure changes to move the rib cage. Modern versions include controls to adjust pressure levels, breathing rate, and the ratio of inhalation to exhalation time.

Why It Matters

The iron lung's historical significance cannot be overstated—it saved thousands of lives during the polio epidemics and represented a major breakthrough in respiratory support technology. Its development demonstrated how mechanical engineering could address critical medical needs, paving the way for modern intensive care and ventilator technology. While largely replaced by more compact positive pressure ventilators since the 1960s, the iron lung taught valuable lessons about long-term respiratory support and patient care. Remarkably, a few patients worldwide continue using updated iron lungs today, preferring them over modern alternatives for comfort and effectiveness in managing their conditions. The device remains an important case study in medical innovation responding to public health crises, and its legacy continues in the design principles of contemporary respiratory assist devices.