ventilator

Machine that assists or maintains breathing when a patient is unable to breathe normally due to illness or injury. There are two modes of ventilation in medical use: positive pressure and negative pressure. The more widely used is the positive pressure ventilator, sometimes popularly known as a ‘life-support machine’. With this, air is blown through an endotracheal tube down the back of the throat to inflate the lungs; the air is exhaled when the pressure from the ventilator is released. Usually this mode of ventilation is only needed for a short time.

The iron lung is an example of a negative pressure ventilator.

The patient lies encased in it, with only the head exposed. A vacuum is created inside the chamber, causing the chest wall to expand and drawing air into the lungs; as the vacuum is released the chest wall subsides, expelling air from the lungs. This mode of assisted ventilation is suitable for people with chronic breathing difficulties, including some polio victims.