Heart-Lung Machine
One of the truly revolutionary pieces of medical equipment has been the invention and development
of the heart-lung machine. Before its introduction to medicine in the 1950s, heart surgery was unheard of;
there was no way to keep a patient alive while working on the heart. Today, about 750,000 open-heart
procedures are performed each year.
During an open-heart surgery, such as bypass surgery, the heart-lung machine takes over the functions of
the heart and lungs and allows a surgeon to carefully stop the heart while the rest of the patient’s body
continues to receive oxygen-rich blood. The surgeon can then perform delicate work on the heart without
interference from bleeding or the heart’s pumping motion. Once the procedure is over, the surgeon restarts
the heart and disconnects the heart-lung machine.
The first heart-lung machine was built in 1937 by physician John H. Gibbon, who also performed the first
human open-heart operation in 1953. Motivated by the death of a young patient in 1931, Gibbon pursued
total artificial circulation for almost three decades in his laboratory at the Jefferson Medical College in
Philadelphia. His first experimental machine used two roller pumps and was designed to replace the heart
and lung action of a cat. But Gibbon’s initial machine was massive, complicated, and difficult to manage.
Its action often damaged or destroyed blood cells, causing bleeding problems and loss of viable blood.
Improvements came in 1945, when scientist Clarence Dennis built a modified Gibbon pump, but Dennis'
machine was hard to clean, caused infections, and never reached human testing. A Swedish physician,
Viking Olov Bjork invented a blood-oxygenating device with multiple screen discs that rotated slowly in a
shaft, over which a film of blood was injected. Oxygen passed over the rotating discs and provided
sufficient oxygenation for an adult human. Bjork, along with the help of a few chemical engineers, one of
whom was his wife, developed a blood filter and an artificial material that they applied to all parts of the
perfusion machine to delay clotting and save platelets. Bjork took the technology to the human testing
phase.
About the same time, Dr. Forest Dodrill, a surgeon at Wayne State University’s Harper Hospital in Detroit,
was developing a machine to detour blood while he repaired patients’ hearts. In a move that combined
engineering and medicine, Dodrill teamed with engineers at General Motors to help him design the device,
which resembled a 12-cylinder engine. The six cylinders on each side of the “engine” were separate
chambers for pumping blood. Doctors later used Dodrill’s machine to perform an open heart surgery in
human clinical trials.
After an interruption in research by his service in World War II, Gibbon joined forces with Thomas Watson
in 1946. This merger also demonstrated the benefits of using engineering to solve a medical problem.
Watson, an engineer and the chairman of International Business Machines (IBM), provided the financial
and technical support for Gibbon to further develop his heart-lung machine. Gibbon, Watson and IBM
engineers improved the original machine to reduce damage to the red blood cells and prevent air bubbles
from entering the blood.
Their new device used a refined method of cascading the blood down a thin sheet of film for oxygenation,
rather than the original whirling technique that could potentially damage blood cells. This new device kept
twelve dogs alive for more than an hour during heart operations. Then, in 1953, Dr. Gibbon performed
open-heart surgery with artificial circulation by closing a hole between the upper heart chambers in an 18year-old girl.
Since those early years, the safety and ease-of-use of heart-lung equipment has gradually improved.
Advances in materials and computing have led to safer, more effective machines. It is now commonplace
for surgeons to stop the heart for several hours while modern heart-lung machines maintain circulation.
Basically, heart-lung machines work by withdrawing bluish, unoxygenated blood from the upper heart
chambers through a tube into a reservoir. From there, the blood is pumped through an artificial lung
designed to expose the blood to oxygen and permit the blood cells to absorb oxygen molecules directly.
Then the blood, now red and rich with oxygen, is pumped back into the patient through a tube connected to
the arterial circulation. The heart-lung circuit is a continuous loop; as the red blood goes into the body, blue
blood returns from the body and drains into the pump to complete the circuit.
Modern heart-lung machines can do a number of other tasks needed for a safe open-heart operation. Any
blood that escapes the circulation and spills around the heart can be suctioned and returned to the pump.
This greatly preserves the patients own blood stores throughout the operation. Also, the patient’s body
temperature can be controlled by selectively cooling or heating the blood as it moves through the heart-lung
machine. Thus the surgeon can use low body temperatures as a tool to preserve the function of the heart and
other vital organs during artificial circulation. Medications and anesthetic drugs can be given via separate
connections. In this way, medications arrive to the patient almost instantly by simply adding them to the
blood within the heart-lung reservoir.
But despite all its advantages, heart-lung machines still carry some substantial risks. These include the
formation of small blood clots in the blood, which, in extreme cases, can cause stroke, heart attack or
kidney failure upon return to the body’s bloodstream. The machine can also trigger an inflammatory
process that can damage many of the body’s systems and organs. Post-operative bleeding may be a serious
complication, occasionally requiring a return to the operating room. Problems with temporary confusion or
memory loss have also been reported in some cases.
Those risks push today’s biomedical engineers not merely to improve the heart-lung machine, but to
develop advances that would eliminate the need for the machine altogether. One such advance is minimally
invasive surgery. Minimally invasive heart surgery is any of several approaches for bypassing critically
blocked arteries that are less difficult and risky than conventional open-heart surgery. These procedures
have the potential benefit of avoiding complications associated with the heart-lung machine, such as
increased risk of stroke, lung complications, kidney complications and problems with mental clarity and
memory. Other benefits are faster recovery and reduced hospital costs. Biomedical engineers are developing
the surgical tools, imaging and robotic technology necessary for minimally invasive surgery.
Another approach is “beating heart” surgery, where the surgeons operate on the heart while it still beats and
moves blood throughout the patient’s body. Recent clinical studies suggest that there may be benefits to
beating heart surgery, such as less trauma to the blood; decreased risk of adverse events, such as stroke; and
a quicker return to normal activities.
One of the greatest challenges in beating heart surgery is the difficulty of suturing or sewing on a beating
heart. A stabilization system makes it possible for the surgeon to carefully work on the patient’s beating
heart, and in the great majority of cases, eliminates the need for the heart-lung machine