How Things Work: The Artificial Heart
The human body consists of 78 organs and 13 organ systems that work collaboratively like a well-oiled machine. Among the most vital is the heart, which pumps 2,000 gallons of blood per day to ensure oxygen and nutrients are being circulated throughout the body. As humans age, the heart may begin to pump less efficiently.
According to the Food and Drug Administration (FDA), each year over 3,000 patients suffering from heart failure need a heart transplant to ensure their survival but have to wait patiently until a donor heart can be found. Unfortunately, only about 2,000 heart transplants are performed annually, leaving a few thousand people without a healthy heart. Fortunately, an artificial heart can be used in the most severe cases to allow patients to return to their daily lives until a suitable donor heart is available.
In order to understand how an artificial heart works, it is first important to know how the four chambers of a normal human heart function. Blood circulates throughout the body by delivering oxygen to other organs from the right atrium of the heart. The heart’s primary function is to pump this blood through the right ventricle to the lungs, where it gets replenished with oxygen. The blood then re-enters the heart at the left atrium and is pumped through the left ventricle to the rest of the body.
During the first stage of a heartbeat, the two atria contract, pumping the blood to the ventricles. During the second stage, the ventricles contract, causing blood to leave the heart through the pulmonary artery to the lungs and through the aorta to the rest of the body.
Contrary to popular belief, an artificial heart only replaces the two ventricles and connects to the natural atrium. Unlike the normal heart, which pumps blood to the lungs and body at same time, an artificial heart can force blood out of only one ventricle at a time.
Currently, there are two leading designs of the artificial heart that utilize different methods to force the blood out of the ventricles.
SynCardia Systems, Inc. has developed a heart with two ventricles separated by a diaphragm, similar to the muscle that expands and contracts in our bodies when we breathe. Blood fills one ventricle and is ejected when an external pump ejects air into the other side of the diaphragm. Howitworksdaily.com states this model has been approved by the FDA —but the only downside is that it requires an external pump weighing about 13-and-a-half pounds that can fit in a backpack.
Having external parts can increase the risk of infection. AbioCor, the artificial heart developed by AbioMed addresses this problem by having all the necessary components inside the body. Instead of a diaphragm and an air pump, this heart uses a hydraulic pump. According to howstuffworks.com, when the hydraulic fluid moves to the right, blood in the right ventricle gets pumped to the lungs. Conversely, when hydraulic fluid moves to the left, the blood in the left ventricle gets pumped to the rest of the body.
Both artificial hearts need a source of energy to ensure that the heart beats continuously so that a patient doesn’t succumb to cardiac arrest. The SynCardia Total Artificial Heart has two external rechargeable batteries and can also be plugged into a wall outlet. The AbiCor heart also has an external battery pack but utilizes a wireless energy transfer system to transmit power through the skin without penetrating the surface.
Generally, the hearts are made of titanium and plastic. One of the biggest challenges is inserting an artificial object into the body and having the body accept it. During a seven-hour surgery, hundreds of stitches are used to attach the artificial device to the patient’s natural tissue with synthetic tissue called grafts.
Artificial hearts have been a growing success as technology continues to improve allowing patients to live longer with the heart without the risk of infection. This past year was monumental for SynCardia Systems, Inc. as the company successfully completed 125 implants. According to the New England Journal of Medicine, 79 percent of patients who receive a transplant survive long enough to receive a donor heart. However, escaping death does have a price — covering the cost of an artificial heart requires about $125,000, and a yearly maintenance fee of $18,000.
After over 900 successful implants, the artificial heart continues to improve so that patients can live longer and infection free. Finding a donor heart, however, is still the best option for patients.