“...I’d be friends with the sparrows and the boys who shoot the arrows, if I only had a heart...well, suppose the wizard wouldn’t give me a heart when we got there?” the Tin Man laments to Dorothy.
Dorothy replies, “Oh, but he will! He must! We’ve come such a long way already...”
And we have, indeed, come a long way in the evolution of the heart pump technology, one of the most important advances in the past century. The amount of heart disease and death by heart failure is only increasing. Heart failure alone kills a shocking 300,000 Americans each year, and heart diseases wipes out at least 600,000, making it the leading cause of death in America. (5) However, with the help of biomedical engineers, we are making progress in tackling the challenge of the rapid rise in death due to cardiovascular disease.
Transplantation of the heart is a tricky and dangerous endeavor. It involves taking out the failing heart and replacing it with a completely new donor heart. One malfunction could immediately extinguish the victim’s life. However, with the right equipment, design, and of course, engineers, millions of lives can be saved. About 35,000 heart transplants from donors are performed around the world. However, donated hearts are not accessible to everyone. In 1998, 7,700 people were on the list for a heart transplant, but only 30% of those people received treatment. That was when the only cure for heart failure was an organ transplant from a donor. (5) Now we have artificial hearts.
Before we delve into the design and inner workings of an artificial heart, we need to know a bit about how the heart actually works. The human heart is a complex organ, responsible for powering all bodily functions. Despite the importance of the heart muscle, the process of pumping blood is fairly straightforward. Essentially, the heart pumps blood from it’s top two chambers, the left and right atrium, into the bottom two chambers, the left and right ventricle, respectively. This process circulates blood through the body. After each contraction of the heart, the muscle relaxes, allowing time for the heart to fill up with blood again. The deoxygenated blood in the left ventricle travels through the lungs via the pulmonary artery to become re-oxygenated and then returns to the right atrium of the heart. The contraction of the heart propels the oxygenated blood in the right ventricle from the heart via the aorta to the rest of the body. After distributing the oxygen to the body, the blood returns, deoxygenated, to the left atrium of the heart, and the process repeats.
Medical engineers have been attempting to create a replacement for the heart since 1911. One of the greatest developments in medical technology in the past century was the invention of the Total Artificial Heart by Willem Kolff, one of his most prolific inventions out of his other revolutionary artificial organ devices. (3)
Thanks to the collaboration of engineers from various fields, the artificial heart has so far been a success in saving lives.
One of the first steps in creating an artificial heart is the design process. Different types of artificial hearts such as the Syncardia, CardioWest, and AbioCor artificial heart systems have varying structures, but are all based on a pump model hat assists the contraction of ventricles. The artificial heart is designed in such a way that it uses an air pump to control the systole—the contraction of the heart, and the diastole—the expansion of the heart. The artificial heart has a shape similar to a normal heart and is attached to the necessary arteries and veins to allow the circulation of blood throughout the body. (4)
Choosing the proper materials is a crucial part in building an artificial heart. Ideally, the materials in an artificial heart should be similar to those of an actual heart while also maintaining durability and flexibility. This is where chemical engineers come into play. The basic framework of the artificial heart is often composed of plastic, titanium, polyurethane, and even animal parts such as heart valves from pigs. An alloy, which is a metallic mixture, primarilycomposed of titanium, aluminum, and vanadium, is used for the pump, motor, and other metallic parts of the heart. A special coating of titanium is used on blood contacting surfaces, allowing blood cells to adhere to the metal, creating a living surface that mimics a real heart. The diaphragm within the pump is made from polyurethane, an easily modifiable, chemical-resistant material, also chosen because blood can easily adhere to its surface. Chemical engineers must carefully choose the right materials to ensure that they are optimal for the function of the artificial heart.
There are different types of systems used to control the contraction, expansion, and distribution of the artificial heart pump.
Pneumatic engineering is categorized under mechanical engineering and deals with air as a power source. The Syncardia and CardioWest artificial heart systems are basically electrical pumps with two internal diaphragms, one in the left ventricle and one in the right that mimics the actual motion of a heart pumping blood. When the diaphragm in the ventricle expands, it provides enough pressure to eject blood. A vacuum supplied by a pneumatic power source pulls the diaphragm down, allowing blood to fill the ventricle. Engineers must manage the systolic function and the diastolic function in the process of pumping blood. Engineers must create the systolic and diastolic function in such a way that each motion happens in the same amount of time in order for pumping of the heart to be synchronized and give the heart a chance to re-fill with oxygenated blood. (2)
An important factor to consider when developing models such as the AbioCor artificial heart is fluid dynamics. The core mechanism of this artificial heart system is a hydraulic pump that actively moves the blood from side to side of the heart. The porting valve in the top middle of the artificial heart opens and closes, allowing blood on the right side of the heart to get pumped through to the lungs through an artificial ventricle when the hydraulic fluid is pushed in the opposite direction. When the hydraulic fluid moves to the left, the blood is pumped to the rest of the body. (1)
In some models of the artificial heart, such as the Syncardia version, the power source is completely external, while in other versions; the electronics package is implanted in the abdomen along with an external power supply. The role of the electrical engineers is to ensure that these power sources are efficient and reliable. The wireless energy-transfer system, or Transcutaneous Energy Transfer (TET) is the main power source for the hydraulic pump artificial heart. Itconsists of two coils, one connected to an external battery pack, and the other connected to an internal rechargeable battery implanted in the patient’s abdomen as well as an internal controller unit that monitors the pumping speed of the heart using ultrasound—high-frequency radio waves that bounce off of blood cells coming out of the heart. The speed and volume of the blood can be determined using this technique, commonly known as radar. (1) We rely on mechanical engineers to ensure that this hydraulic system works 24/7 and electrical engineers to create a faultless electrical system.
As in any process that tests the efficiency of a device, mechanical engineers must test how the artificial heart would respond under the pressures of the human body. To do this, the artificial heart is connected to a machine called a mock loop, which imitates the natural pressures of the human body. This allows engineers to create certain scenarios that could be seen in a patient and train the heart to respond to these scenarios. (4)
Now that scientists know how to replace one of the most important organs in the body with a mechanical pump, they can work on developing technology to improve other complex aspects of the heart. Currently, the transplantation of the artificial heart is a temporary solution and can only extend a life for a few years. Thanks to engineers, we are rapidly progressing in the development and improvement of the artificial heart. Researchers are currently working on creating a longer last and potentially permanent artificial heart. We have come so far in the development of this technology that we are able to do what only a few years ago we might have thought as impossible. Instead of the Wizard of Oz, we have biomedical engineers, the true geniuses of modern technology in health.