Such valves were first described by the American dentist Jay Heidbrink, who used a thin disc that was held in place by a spring. The valve is<unk>  and spring-loaded, allowing the opening<unk>  of the valve to be controlled by screwing the valve top which modifies the<unk>  on the spring. A very light spring is used, so that at its minimum setting the valve can be opened by the patient's breathing alone using low<unk> s. In contemporary APL valves, three orifices or "ports" are present: one for intake of gas, one for return of gas to the patient, and an exhaust port for waste gas which can be connected to a scavenging system.
Adjustable pressure-limiting valve
Articulatory technique
Artificial heart valve
Artificial cardiac pacemaker
Tissue engineering of heart valves
Minimally invasive cardiac surgery
Minimally invasive direct coronary artery bypass surgery
Cardiac pacemaker