In 1927, the first iron lung (electric respirator) was
installed at Bellevue hospital in New York for the post war polio epidemic. The
first iron lung was developed at Harvard University by Phillip Drinker and
Louis Agassiz Shaw built with two vacuum cleaners.
The iron lung is a negative pressure machine which
surrounds the patient's body except for the head, and alternates a negative
atmospheric pressure with the ambient one, resulting in rhythmic expansion of
the chest cage (and thus inhalation) in response to the negative extra thoracic
pressure. During periods of ambient extrathoracic pressure, the lungs deflate.
Humans, like most animals, breathe by negative pressure
breathing: the rib cage expands and the diaphragm contracts, expanding the
chest cavity. This causes the pressure in the chest cavity to decrease, and the
lungs expand to fill the space. This, in turn, causes the pressure of the air
inside the lungs to decrease (it becomes negative, relative to the atmosphere),
and air flows into the lungs from the atmosphere: inhalation. When the
diaphragm relaxes, the reverse happens and the person exhales. If a person
loses part or all of the ability to control the muscles involved, breathing
becomes difficult or impossible.
The person using the iron lung is placed into the central
chamber, a cylindrical steel drum. A door allowing the head and neck to remain
free is then closed, forming a sealed, air-tight compartment enclosing the rest
of the person's body. Pumps that control airflow periodically decrease and
increase the air pressure within the chamber, and particularly, on the chest.
When the pressure is below that within the lungs, the lungs expand and
atmospheric pressure pushes air from outside the chamber in via the person's
nose and airways to keep the lungs filled; when the pressure goes above that
within the lungs, the reverse occurs, and air is expelled. In this manner, the
iron lung mimics the physiological action of breathing: by periodically
altering intrathoracic pressure, it causes air to flow in and out of the lungs.
The iron lung is a form of non-invasive therapy.
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