Negative pressure ventilator

A negative pressure ventilator (NPV) is a type of mechanical ventilator that stimulates an ill person's breathing by periodically applying negative air pressure to their body to expand and contract the chest cavity. 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. Another form of NPV device (such as the Pulmotor) is placed at the patient's airway, and alternates negative pressure with positive pressure to pump air into their lungs (inhale under positive pressure), then suck it back out (exhale under negative pressure). 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. However, researchers and clinicians still find some uses for NPVs, owing to their specific advantages. Research and developments in artificial ventilation, both negative-pressure and positive-pressure, result in evolving assessments of the benefits and hazards of negative-pressure ventilators (NPVs). Different researchers and clinicians have made varying assessments, over time, about the primary positive and negative aspects of NPVs. A sampling includes: Generally, NPVs are best with patients who have neuromuscular diseases, but normal lung compliance (a measure of the lungs' ability to expand and contract).(1988: Grum & Morganroth, Journal of Intensive Care Medicine) They are effective for various conditions, especially neuromuscular and skeletal disorders, particularly for long-term night-time ventilation.