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A Heart-Lung Machine (HLM) is a device that temporarily takes over the function of the heart and lungs. This technique is referred to as Cardiopulmonary Bypass (CPB). Heart-Lung Machines are operated by allied health professionals known as Perfusionists. It is an extracorporeal therapy.
Uses of the heart-lung machine Heart-Lung machines are commonly used in heart surgery because of the difficulty of operating on the beating heart. Operations requiring the opening of the chambers of the heart require the use of the HLM to support the circulation during that period. HLMs can be used for the induction of total body hypothermia, a state in which the body can be maintained for an hour or more without perfusion (blood flow). If blood flow is stopped at normal body temperature, permanent brain damage normally occurs in three to four minutes — death may follow shortly afterward. HLMs are also sometimes used as life-support for newborns with serious birth defects, or to oxygenate and maintain donors for organ transplantation. Surgeries in which Heart-Lung Machines are used Components of a Heart-Lung Machine Heart-Lung Machines consist of two main functional units, the pump and the oxygenator. Roller Pumps The pump console is usually comprised of several rotating motor-driven pumps that peristaltically "massage" tubing made of silicone rubber, or PVC. This action gently propels the blood through the tubing. This is commonly referred to as a roller pump, or peristaltic pump. Centrifugal Pump Many HLMs now employ a centrifugal pump for the maintenance and control of blood flow during CPB. By altering the speed of revolution (RPM) of the pump head, blood flow is produced by centrifugal force. This type of pumping action is considered to be superior to the action of the roller pump by many because it is thought to produce less blood damage (Hemolysis, etc.). Oxygenator The oxygenator is a device designed to transfer gas to and from the blood. Today's oxygenators are made of materials that allow gas diffusion across a membrane (polypropylene, silicone, etc.) This allows for oxygenation of de-oxygenated blood and removal of CO2 from the venous blood. Another type of oxygenator gaining favor recently is the heparin-coated blood oxygenator. History John Gibbon is credited with developing the first truly practical heart-lung bypass machine and performed the first successful surgery with it in May 1953 in Philadelphia, an atrial septal defect repair. See also | ||||||||
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