Iron lung

The iron lung emerged in 1928 at Harvard not because Philip Drinker was brilliant, but because polio epidemics were paralyzing children's respiratory muscles faster than hospitals could respond. By the late 1920s, severe poliomyelitis was crippling thousands. Respiratory failure killed within hours. Drinker and Louis Agassiz Shaw needed a way to breathe for patients whose diaphragms had stopped working.

The solution exploited negative pressure. The iron lung was an airtight metal cylinder enclosing the patient's body from the neck down. Air pumps cycled pressure inside the chamber: negative pressure expanded the chest, drawing air into the lungs through the patient's mouth; positive pressure compressed the chest, forcing exhalation. The patient's head remained outside, allowing them to see, speak, and eat while the machine breathed for them.

This represents exaptation: the repurposing of biological respiratory principles—chest expansion through external pressure—into medical technology. What the iron lung constructed was not an ecological niche but technological path-dependence. Hospitals built around iron lung wards, manufacturers tooled for production, doctors trained in negative pressure ventilation. Institutions locked in around one solution.

The first clinical test came on October 12, 1928, at Boston Children's Hospital. An eight-year-old girl, nearly dead from respiratory failure, was placed inside the chamber. Within one minute, she revived. The dramatic recovery convinced skeptics. By 1939, around 1,000 iron lungs operated across the United States.

But the iron lung revealed its fatal flaw in Copenhagen in 1952. The Blegdam Hospital faced a polio epidemic overwhelming capacity. Mortality rates hit 87%. Patients in iron lungs drowned in their own saliva—the machine breathed for them, but paralyzed swallowing muscles allowed fluids to pool in their airways. Fatality rates reached 80-90%. The iron lung's descendants aren't iron lungs—they're the opposite.

Danish anesthetist Bjørn Ibsen proposed the alternative: tracheostomy and positive pressure ventilation. Instead of pulling air into the lungs by expanding the chest from outside, blow air directly into the airways through a tube inserted in the throat. The method came from operating rooms, where anesthetists had used positive pressure to maintain breathing during surgery.

The intervention required 1,400 medical students working in shifts, manually squeezing breathing bags to ventilate patients around the clock. Mortality dropped from 87% to 25%, then to 11%. The overwhelming manpower demand forced innovation: adapt the positive-pressure machines from operating rooms for continuous use. This created the modern intensive care unit.

The iron lung exhibited niche construction in reverse—its inadequacies created selection pressure for a replacement. This is competitive-exclusion in medical technology: when a superior solution emerges, the inferior technology can't coexist. Positive pressure ventilation, enabled by endotracheal tubes with high-volume, low-pressure cuffs, made iron lungs obsolete by the 1960s.

Today, ICUs worldwide use positive pressure ventilation for respiratory failure from any cause. The conditions created the technology; the technology's failure created the conditions for its replacement. Path-dependence can be broken when mortality rates force reexamination of first principles.

A handful of polio survivors still use iron lungs in 2026, unable to transition to modern ventilators after decades of adaptation. These machines, built in the 1950s and maintained through scavenged parts, represent the endpoint of a technological lineage that its own success rendered obsolete. The polio vaccine eliminated the disease; positive pressure ventilation eliminated the iron lung. Both solved the problem more directly than the cylindrical chambers that bought time while better solutions emerged.