Negative pressure ventilator

Negative pressure ventilator
Intervention
An Emerson iron lung. The patient lies within the chamber, which when sealed provides an effectively oscillating atmospheric pressure. This particular machine was donated to the Centers for Disease Control and Prevention Museum by the family of poliomyelitis patient Barton Hebert of Covington, Louisiana, who had used the device from the late 1950s until his death in 2003.
ICD-9-CM	93.99
MeSH	D015919
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A negative pressure ventilator, often referred to colloquially as an iron lung, is a form of medical ventilator that enables a person to breathe when normal muscle control has been lost or the work of breathing exceeds the person's ability. Examples of the device include both the Drinker respirator and the Both respirator. The negative form of pressure ventilation has been almost entirely superseded by positive pressure ventilation or biphasic cuirass ventilation.

Humans, like most mammals, 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.