Respirator

Negative pressure ventilators do not pump air into the lungs. Instead they expand the chest to suck air into the lungs. These respirators come in three types: the tank, the cuirass, and body wrap.

The tank negative pressure respirator is commonly called the iron lung. Familiar during the poliomyelitis epidemic of the 1950s, the tank is a cylindrical container into which the patient is placed with his head protruding from an opening at one end. Air in the tank is sucked out periodically, which expands the patient's chest to force him to inhale. Then the pressure in the tank is normalized and the patient exhales. Of course, the patient in an iron lung is immobile. One side effect of long-term iron lung occupancy is the possibility of so-called tank shock, the pooling of blood in the patient's abdomen, which reduces venous return to the right atrium of the heart.

A more convenient form of negative pressure respirator is called the cuirass, or chest shell. It is a molded, plastic dome that fits closely to the patient's body over the chest. As in the iron lung, the air is pumped out of the cuirass, which forces the chest to expand and air to be pulled into the lungs. When the pressure is normalized the chest relaxes and the patient exhales. The primary problem with the cuirass is that a poorly fitted one can cause pressure sores at the points where the seal is not adequate.

The pulmowrap is an impervious wrapping placed around the patient and connected to a pump. Here again air is removed from the wrap to expand the lungs.