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Cardiac pump
A cardiac pump or cardiac bypass pump or heart-lung machine temporarily
takes over the function of breathing and pumping blood for a patient.
It generally has two parts, the pump and the oxygenator.
The pump is usually several motor-driven rollers that
perstaltically massage a tube made of silicone rubber. The massage
pushes the blood through the tubing. This is commonly referred to
as a roller pump. Another type of pump is a centrifugal pump. The
blood enters a small centrifuge, and propels the blood forward via
centrifugal force. The oxygenator varies, but usually is a passage
through a silicone-membrane simulated lung known as a true membrane
oxygenator.
Cardiac pumps are most often used in heart surgery,
so that a patient's heart can be disconnected from the body for
longer than the twenty minutes or so it takes a prepared patient
to die. Although unprepared patients get brain damage in three to
four minutes, a patient can be prepared by cooling and drugs so
that no damage will occur for twenty minutes or more.
The perfusionist opearates the heart-lung machine.
Cardiac pumps are also sometimes used to keep babies
with birth defects alive, or to aerate bodies with transplantable
organs.
Chronic use of cardiac pumps is contraindicated because
the pressure profile of most practical pumps is believed to cause
circulatory damage to the brain, especially in extended use. The
pumps generate continuous pressure. When this pressure is set high
enough to aerate tissues in the foot, it can easily damage tissue
in the brain. Likewise, if set low enough to avoid damaging the
brain, it often under-aerates some part of the body, such as the
feet.
In France, emergency medical teams (SAMU) use a different
kind of portable cardiac pump which stimulates blood circulation
by suction. This is used primarily for treating heart attack victims.
Russell M. Nelson worked on the team that developed
the first heart-lung machine.
Dr. John H. Gibbon Jr. perfected the first truly practical
heart-lung bypass machine and performed the first successful surgery
with it in May 1953 in Philadelphia.
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