more on the operative procedure. The article has described what the CBM is used for today. In order to understand how engineering has helped to shape this modern technology, it is necessary to take a look at the history of the development of the CBM.
The first heart-lung machine was built by John Gibbon in 1937. This machine used two roller pumps and the machine had sufficient capacity to replace the heart and lungs of experimental cats. The machine was too small to serve for dogs or humans. Most animals died from the haemolysis( clotting of blood), air embolism introduced into the body, and blood-foreign surface interaction. The problem of haemolysis was alleviated somewhat in 1939 when the anticoagulant Heparin was discovered.
John Gibbon, who was a physician, met an engineer by the name of Thomas Watson in 1946. This engineer was also the chairman of IBM (International Business Machines). Watson was able to provide both financial and technical support to Gibbon to help in the development of heart-lung machine. Watson along with 5 other engineers helped Gibbon to invent a machine that minimized haemolysis and prevented air bubbles from entering the circulation. This heart-lung machine was contained within a cabinet that kept the body at normal temperature and blood flow was carefully controlled to maintain a constant blood volume. With the invention of this new machine, there was only a 10% mortality in dogs, whereas the mortality rate had been 80%.
About the same time as Gibbon was working on his heart-lung machine, Bill Bigelow was also doing open heart operations on dogs but he was using a different approach. Bigelow was using cooling blankets and ice bags to cool the dogs to 20 degrees Celsius (68 degrees Fahrenheit). The oxygen consumption of the heart fell to 15% of normal, thereby allowing the heart to be isolated from circulation for 15 minutes to allow for an operation with a better survival rate than previously found.
Clarence Dennis in 1945 set out to build a mechanical heart-lung appartus that would permit complete bypass of the heart and lungs during surgical operations of the heart. Dennis built a modified Gibbon pump. Dennis needed an oxygenator that would do the following: use a minimum amount of blood, do as little damage to the blood cells as possible and to acheive a critical level of oxygenation without excess foaming. This new pump consisted of a nest of vertically revolving stainless steeel cylinders. These were mounted over a revolving funnel in which the blood, oxygenated on the walls of the cylinders, was collected. New roller pumps were used to cause less haemolysis. This apparatus was cumbersome and difficult to clean. Most dogs died during the testing of this machine either during perfusion or shortly afterwardss. Dennis discovered that the oxygenator was contaminated and many of the animals died from infections. The method of sterilization along with the design of the oxygenator was changed.
In Sweden, a physician by the name of Viking Olov Bjork had invented an oxygenator with multiple screen discs that rotated slowly in a shaft, over which a film of blood was injected. Oxygen was passed over the rotating discs and provided sufficient oxygenation for an adult human. Bjork along with help of a few chemical engineers, one of which who was his wife, prepared a blood filter and an artificial intima of silicon under the trade name UHB 300. This was applied to all parts of the perfusion machine, particularly, the rough red rubber tubes, to delay clotting and save platelets.
The first heart lung bypass machine was first used on a human in 1953. In 1960, it was considered safe to use the CBM along with hypothermia to perform CABG surgery. Heat exchangers were used to cool and rewarm the blood. Using these heat exchangers helped to eliminate the tedious process of surface cooling.
The CBM has not changed much in the past 30 years. The CBM is a large machine that takes up a lot of room in an operating room. Engineers are working on designing a smaller unit that will not take up as much room. This is