A. A ventilator is breathing machine. It could be as simple as a flexible plastic bottle squeezed by hand or as complex as a machine controlled by a computer and powered by electricity or compressed gas. The large 1930s polio-era iron lungs are ventilators. Hospital ventilators today are about the size a microwave oven and often are on wheeled stands, with large monitors for medical workers to keep track of how a patient is responding to treatment. The federal government and state governments are working to avoid a shortage of ventilators should hospitals face a crush of patients in need of the lifesaving machines that help them breathe.