A cough assist device is a machine that helps clear secretions from the lungs for people with a weak cough. It works by using a rapid change in air pressure, first applying positive pressure to inflate the lungs and then negative pressure to quickly pull air out, which mimics and strengthens a natural cough. This mechanical insufflation-exsufflation is used for conditions like neuromuscular disorders, spinal cord injuries, or severe fatigue, and is applied through a mask, mouthpiece, or a tracheostomy tube.