The iron lung was one of the most important life-support machines of the 20th century. It helped many people with paralytic polio survive when the muscles used for breathing became too weak to move air in and out of the lungs. The device shows how engineering, pressure, and human biology can work together to solve a medical emergency.
It also marks an important step in the history of intensive care and mechanical ventilation.
An iron lung works by changing the air pressure around a patient’s chest while the head remains outside the sealed chamber. When pressure inside the chamber drops below atmospheric pressure, the chest expands and air flows into the lungs. When the pressure rises again, the chest relaxes and air flows out.
Modern ventilators usually use positive pressure, which pushes air into the lungs through a mask or tube, but both systems are designed to support gas exchange when the body cannot breathe effectively on its own.
Key Facts
- The iron lung is a negative-pressure ventilator that surrounds the body but leaves the head outside the chamber.
- Air flows from higher pressure to lower pressure, so pressure differences drive breathing.
- During inhalation, chamber pressure decreases and the patient’s chest expands.
- During exhalation, chamber pressure increases and the patient’s chest recoils.
- Pressure difference can be written as ΔP = Poutside - Pinsidethechamber.
- Modern positive-pressure ventilators push air into the lungs, while iron lungs pull the chest outward by lowering pressure around the body.
Vocabulary
- Iron lung
- An iron lung is a sealed mechanical respirator that helps a person breathe by changing the air pressure around the body.
- Negative pressure
- Negative pressure means a region has lower pressure than its surroundings, causing air or tissue to move toward that region.
- Ventilation
- Ventilation is the movement of air into and out of the lungs.
- Polio
- Polio is a viral disease that can damage motor nerves and sometimes paralyze the muscles needed for breathing.
- Diaphragm
- The diaphragm is a dome-shaped muscle below the lungs that contracts to help draw air into the body.
Common Mistakes to Avoid
- Thinking the iron lung pumps air directly into the lungs. It actually changes the pressure around the chest so the patient’s own lungs fill and empty.
- Confusing negative-pressure ventilation with positive-pressure ventilation. Negative pressure pulls the chest outward, while positive pressure pushes air into the airway.
- Assuming the iron lung cured polio. It supported breathing while the patient’s nervous system was affected, but it did not destroy the virus or repair nerve damage.
- Ignoring the role of pressure difference. Air movement depends on a pressure gradient, not simply on the machine being turned on.
Practice Questions
- 1 An iron lung lowers the chamber pressure from 101.3 kPa to 100.5 kPa while the patient’s airway remains at 101.3 kPa. What is the pressure difference driving inhalation?
- 2 A respirator runs at 12 breaths per minute. How many breathing cycles does it complete in 3 hours?
- 3 Explain why an iron lung can help a patient with paralyzed breathing muscles even though it does not place a tube into the lungs.