*Ever since the development of positive pressure nasal and face interfaces, negative pressure is not used commonly.*

Negative pressure ventilation works of the mechanism of delivering pressure which is sub-atmospheric resulting in the expansion of the chest and air being drawn into the lungs through the nose and mouth. When the pressure which is around the chest wall returns to normal pressure of the atmosphere there shall be passive expiration. Negative pressure ventilation endeavors to mimic normal breathing mechanics.

Methods for providing negative pressure ventilation include iron lung which was used primarily in the epidemic of polio in the era of 1950's.Curiass/shell is a shell or a cage which surrounds the chest and is then connected to a portable ventilator.

Raincoat or Poncho is a tight fitting suit which is connected through the means of hoses to a portable ventilator. Rocking bed is another method for providing negative pressure ventilation which induces diaphragmatic motion by placement of the patient on a bed which rocks rapidly flat to upright while the contents of abdomen shift. A pneumobelt is a belt with a bladder which can inflate and deflate with air in a cyclic pattern. The diaphgram moves in response to changes in the intraabdominal pressure. Another form of negative pressure ventilation is a pneumowrap.

Indications for negative pressure ventilation include chronic respiratory failure secondary to neuromuscular disease- polio, muscular dystrophy. Generally used for nocturnal ventilatory support, with the patient breathing spontaneously during the day. Negative pressure ventilation has also been used in acute respiratory failure, there are 2 different studies which examined the use of the iron lung and poncho wrap (respectively) in COPD patients with acute respiratory failure. Both studies demonstrated the effectiveness of negative pressure ventilation to correct CO2 retention.

Drawbacks encountered with negative pressure ventilation are worsening of obstructive sleep apnea, problems with correct fitting as well as portability issues. Attendants are often required for the application and removal of the device making the process troublesome for the patients. For the use of negative pressure ventilation the patients must sleep in supine position only making it difficult to use.
