Negative pressure ventilator

cylinder (black), patient head exposed through sealed opening. Diaphragm (yellow) mechanically extends, and then retracts, varying cylinder air pressure and causing the patient's chest to expand (top), and then contract (bottom) In most NPVs (such as the iron lung in the diagram), the negative pressure is applied to the patient's torso, or entire body below the neck, to cause their chest to expand, expanding their lungs, drawing air into the patient's lungs through their airway, assisting (or forcing) inhalation. When negative pressure is released, the chest naturally contracts, compressing the lungs, causing exhalation. In some cases, positive external pressure may be applied to the torso to further stimulate exhalation. ==Usage==

Negative pressure ventilators, while widely used in the early-to-mid 20th century (particularly for victims of the polio epidemics), are now largely replaced by positive-pressure airway ventilators, which force air (or oxygen) directly into the patient's airway. Continuous external negative pressure ventilation (CENPV) was found in a 2015 study to "[improve] oxygenation under [a greater number of] physiological conditions", concurrent with lower "airway," "transpulmonary," and "intra-abdominal" pressures, than experienced with continuous positive pressure ventilation (CPPV), in study of adult respiratory distress syndrome (ARDS) patients, possibly reducing high ARDS mortality. Disadvantages NPVs do not work well if patient's lung compliance is decreased, or their lung resistance is increased. ==Types of NPVs==

There are several types of NPVs, including: • jacket ventilator, also known as a poncho or raincoat ventilator; Exovent The exovent is a modern device similar to the cuirass ventilator, but developed in 2020, in response to the COVID-19 pandemic. Positive-and-negative pressure ventilator Pulmotor The Pulmotor is a device developed in the early 1900s which was the forerunner of modern mechanical ventilators. It used pressure from a tank of compressed oxygen to operate a valve system that alternately forced air into and out of a person's airway, using alternating positive and negative air pressure. Although portable, and able to be used by lay persons and non-medical emergency responders, some medical personnel criticized it as dangerous (in part due to the risks of barotrauma or vomiting) and inefficient. == References ==