Changing Your Mind: The Science of Transplanting a Human Head

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Image used with permission; Pfree2014, via Wikimedia Commons. 

In 1967, a surgeon in South Africa successfully carried out the first human heart transplant. Doctor Christiaan Barnard performed the operation on a 53-year-old man dying from chronic heart disease. Although the man died two and half weeks later (from pneumonia), the transplant was touted as a revolutionary step forward in modern medicine.  

Flash forward fifty years. Cardiac transplant procedures will be performed more than 3,000 times this year alone. And these days, your ticker isn’t the only organ that can be swapped out. Kidneys, livers, lungs, corneas ­­– almost every part of your body can be replaced by the same part from another person.

So why not transplant a whole body?

In early 2018, an Italian doctor named Sergio Canavero is planning to do just that. With a team of more than 150 medical professionals, Canavero will attempt the world's first human "head transplant" – a misleading name for the procedure in which a person’s body from the neck down will be replaced with a different body. (The body will likely come from an individual with brain-death, but who is otherwise healthy.) The surgery will last 36 hours, and will cost an estimated $20 million dollars.

Valery Spiridonov, a 30-year-old Russian computer programmer, was initially scheduled to be the first patient of this experimental procedure. Spiridonov was born with Werdnig-Hoffmann disease, a terminal muscle-wasting degenerative disorder better known as spinal muscular atrophy. The disease impairs basic functions such as eating and breathing, and has necessitated that he use a wheelchair from an early age. Spiridonov has already lived longer than most people with the disease (most do not survive past the first few years in life) which makes him an ideal volunteer for Canavero’s scalpel.

Spiridonov volunteered for the sake of advancing our understanding of the science of medicine. In his words:

“This technology is similar to the first man to walk in space. This is because in the future it will help thousands of people who are in an even more deplorable state than I am.”

Despite his initial enthusiasm for the surgery, Spiridonov recently declined to undergo this risky treatment. Instead, he’s opting for a more conservative surgical approach that will aim to repair his skeletal structure by straightening the spinal column with implants. Nevertheless, Canavero and his team intend to push forward with the procedure. The surgery is slated to take place at Harbin Medical University in China, so the final candidate is likely to be Chinese citizen with a similarly terminal illness.

So how will this work exactly? Although it sounds dramatically more complex than other well-tested transplant procedures, a body transplant essentially must overcome the same hurdles.

First, both the body and the head must remain at very cold temperatures. Low temperatures slow down molecular and cellular processes, including the biochemical signaling pathway that results in cell death. Therefore, Canavero and the team plan to operate at 12 degrees C (54 degrees F) to lengthen the time window for operation and reduce the risk of irreparable cell damage.

Sergio Canavero

Pictured above: Dr. Sergio Canavero, the Italian surgeon who will perform the world's first "human head" transplant. Image used with permission under Creative Commons.

During surgery, the brain will be separated from the lungs and heart. As a result, oxygenated blood will not be able to reach the brain. Without oxygen and sufficient blood pressure in the head, the brain goes into a comatose state within minutes, and dies soon after. To avoid this, the team is planning to oxygenate the brain by running a special oxygen-carrying compound called Perftoran through the blood vessels. This compound delivers oxygen much the same way hemoglobin does in normal blood.

The most difficult challenge may be reattaching the delicate nerve fibers from the recipient head to the donor body. If the nerve fibers had been damaged in something like a traumatic spinal-cord-crushing car accident, they would be frayed and inflamed. But in the carefully-controlled environment of the surgical theatre, Canavero’s team can cleanly and precisely cut nerve fibers to minimize inflammation. 

So how will the nerves from the head find the appropriate counterpart from the body and create fully-functioning neural network? Dr. Xiaoping Ren, a member of Canavero’s international team of researchers and surgeons may have the answer. Ren has used a compound called polyethylene glycol (PEG) to reconnect severed nerves.

PEG is not a particularly novel compound. It is already known to have a wide variety of applications. In medicine, it is often used as a laxative for flushing out the digestive system before certain surgical procedures. It has also preserved the natural clay colors of the famous Terra Cotta warriors after they were unearthed in Xian, China. Odds are, it is even in your favorite brand of toothpaste. In Ren’s lab, however, it has been used to repair the spinal cords of surgically paralyzed rats.

In Ren’s study, the spinal cords of 15 rats were completely severed at the 10th thoracic level of the spinal column - roughly at the midback in humans. This prevented the legs from receiving any signals from the brain, resulting in complete paralysis. The experimental group was given PEG at the site of the injury, while the control rats received saline. In just under 4 weeks, the PEG-treated rats were moving around in their cage while their saline-injected counterparts were still unable to walk. PEG acted as a biological “glue” for reconnecting severed nerves. And if PEG  repairs surgically-induced nerve damage in rats, it may do the same in humans.

At first pass, the idea of a body transplant may seem off-putting or even downright disturbing. Canavero’s critics have already been adamantly vocal against his intentions to conduct this surgery. But this type of resistance often accompanies forward-thinking scientific advances. From Copernicus’ rejection of the geocentric model of the solar system to Edward Jenner’s administration of life-saving vaccinations, major advances in understanding our natural world and medical science have almost always been met with opposition. In the end, this transplant procedure will teach us much about the yet-unexplored potential for surgery and post-surgical healing in the future.

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