Abstract: An involuntary respiratory apparatus for perfusing and entraining a breathable liquid from the lungs of a patient. The system includes a number of components which are interconnected by a conduit so as to form a substantially closed loop, single path circuit. The various components include a reservoir, a pump, an oxygenator, a heat exchanger, an endotracheal tube, a Y-connector, a valve and a controller. To simulate inspiration, the controller closes the valve, which is located downstream of the Y-connector, thereby forcing the liquid into the lungs of the patient. After a tidal volume of liquid has been perfused into the patient's lungs, the controller opens the valve. The Y-connector is shaped such that the flow of liquid through its inspiratory limb will cause the liquid in the patient's lungs to be entrained into the flow out of the Y-connector. In this manner, the Y-connector operates as an ejector pump and allows the apparatus to continuously perfuse the liquid through the single path circuit.