Components of the Heart Lung MachinePublished on 2/8/2018 & updated on 6/8/2018
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Blood PumpsThe general characteristics of blood pump are as follows.
- It should pump up to 6 liters / minute regardless of the outflow pressure
- Pumping action should not affect the blood components
- Easy to clean and replace
- The calibration of pump should be done carefully
Pulsatile PumpThere are two chambers in the pulsatile pumps namely inner and outer chamber. The inner chamber is compressed when the blood is injected into the outer chamber. There is an outflow valve, through which blood is ejected. After the blood is completely ejected, the inner chamber becomes normal shaped. After this, again, blood pump is filled with blood and the same process continues.
Non-Pulsatile PumpIn this type, a roller is used to squeeze the tube filled with blood. This generates non-pulsatile blood flow. The most commonly used non-pulsatile pump is the roller pump as shown in figure below. The tube carrying blood is placed in-between pump housing and the roller. The tube has a tendency to move forward when the roller passes over it. So it is provided with a stopper to stop its movement. So when the roller moves, the blood in the tube also moves forward. The clearance between the pump and roller can be controlled automatically which helps to prevent high pressure on the blood flowing in the tube.
Traps and FiltersThese are used to control and prevent problem of embolism during bypass. Air embolus is an air bubble that is introduced during the circulation. Large embolus has blood clots, tissue particles that are mixed with blood and it blocks the artery. Whereas, small emboli are produced due to fat globules and red cells. So traps and filters are used to prevent these embolisms from reacting with the circulatory system.
Heat ExchangerUsed to regulate the body temperature at 37oC. It is used to reduce the blood temperature during surgery procedure. Under hypothermia condition, after surgery procedure heat exchanger is used to rewarm the blood. Heat exchange is done by two methods. In external heat exchange method, heat exchanger is added to the blood circuit directly.Another method is heat exchanger is built within the oxygenator itself.
OxygenatorsThey perform the functions of lungs. It is also called as Artificial Lung. An ideal oxygenator should oxygenate 5 liters of blood per minute. Various types of oxygenators are available.
Bubble OxygenatorsIn this method, oxygen is bubbled through blood column. The blood is made to flow in a slanting path. By this carbon dioxide is removed from the blood. To remove the bubbles from the blood, beads, sponges and mesh coated with silicon are used. Silicon reduces the surface tension of bubbles and prevents the bubble formation. Hence, the embolism is prevented.
Film OxygenatorsIn this method, a thin layer of blood is applied on the rotating disc or metal screen. An oxygen mixture flows on this thin layer of blood. Horizontal cylinder is the shape of rotating disc type. It rotates at a speed of 120 RPM. The blood is at lower level. On top of it a layer of blood is spread. Oxygen is given to the oxygenator. The blood is washed from the disc.
Membrane OxygenatorsIn this method, oxygenation happens when oxygen and blood flows in opposite direction via thin porous membrane. Blood flows on one side of the membrane and oxygen flows on other side of the membrane.
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