Negative pressure ventilator

When negative pressure is released, the chest naturally contracts, compressing the lungs, causing exhalation.

Different researchers and clinicians have made varying assessments, over time, about the primary positive and negative aspects of NPVs.

[11] 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.

[2] They result in a greater vulnerability of the airway to aspiration, such as inhalation of vomit or swallowed liquids, than with intermittent positive pressure ventilation.

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.

Iron lung 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)