Photo credit: Pixabay
Last month we celebarted Valentines Day and World Marraige day. Throughout the month of February, even the most Hallmark-hating individuals find ways to express their love to the dearest. Love is the word and there is no part of the body more closely linked to love than the heart. A strong contender for the most important organ in the body, the heart is the pump that keeps each one of us alive. However, as any engineer will tell you, sometimes pumps break and can’t be repaired. Whilst they can be replaced, the question is what with? A viable, transplant-ready heart is a rarity and with one person having a heart attack every five minutes in the UK, it was only natural that we look for a more mechanical alternative .
Since World War II doctors have earnestly considered machines as replacements for the human heart. Pumps of all shapes and sizes exist everywhere, so why not inside us? To understand the difficulty involved in implementing an artificial heart, it is important to understand what the organic heart undergoes.
The average human heart weighs around 280g, or 10oz, and pushes about five and a half litres of blood throughout the body with no external power source . Two of the biggest problems with artificial hearts are the body’s natural defence against foreign objects rejecting the heart, and the power source needed to drive the pump. The first artificial heart, used in 1982, required the user to remain in a bed next to its power source. Whilst it succeeded in keeping him alive for the 112 days he used the device, the limitations on his quality of life were at times unbearable . Thankfully, power supplies have gotten smaller, and we have a better understanding of the body and materials which help reduce the chances of rejection.
What is most impressive about the heart, however, is how often it beats. Everyday an average of 100,000 ‘duh-dums’ ring out of our chests, and this happens for as long as we live without rest. Replicating this incredible display of stamina using plastic and metal for a comparable length of time has proved impossible thus far and is the main reason artificial hearts are seen as a ‘bridge to transplant’ technology. However, just as we took to the skies without mimicking a bird’s flapping wing, scientists have been designing artificial hearts that do not beat. This has resulted in animals, and even some people, living without a pulse.
Numerous teams around the world have developed different versions of artificial hearts, that push blood around the body in a continuous flow instead of spurts. Archimedes Screw pumps or centrifugal pumps, both of which produce continuous flow, have been used for years to assist weak hearts in Left Ventricle Assist Devices (LVAD) [4,5]. The benefit of these is that they do not need an air supply to inflate and deflate the heart, making them less cumbersome. These are used to help support the heart as it recovers which is an ideal end result for any treatment. However, this idea is now being applied to complete artificial hearts. Notably, Dr O.H. Frazier and Dr Billy Cohn were able to keep Craig Lewis, a 55 year-old man, alive for five weeks with their continuous flow artificial heart . Lewis unfortunately passed away due to a failure of his liver, but he left behind confirmation that humans don’t need a pulse to remain alive. There have been instances of people who have had LVADs installed, living normal lives after the LVAD became the sole propeller of blood through their bodies, but Lewis’s case is proof that it can be done intentionally and safely.
An example of a Left Ventricle Assist Device. Two LVADS are combined to make the artificial heart. Credit: Steven M Gordon (Wikimedia Commons).
The continuous flow artificial heart is still undergoing much testing; investigation into the long term effects of living without a pulse need to be determined. The human body is a well-oiled machine that has evolved to function with a pulse, and though there has been no evidence of problems in people and animals living pulseless lives, the youth of the technology limits the certainty with which the artificial hearts can be greenlighted. Yet the completion of this technology could see organ waiting lists shrink dramatically and heart failure being far from a death sentence. The labours of doctors and engineers could lead to people living out full lives without that tell-tale sign we’ve grown so accustomed to: a pulse.
Check the New Scientist link for a video of the Mollusk. https://youtu.be/ErCOTdIruoc