The journey to discover the heart’s function dates back thousands of years to the time of the Romans and Greeks. Romans knew not only of the hearts significance to life but also attributed the organ to possessing the soul of human. Despite their limited understanding of the heart they did know that once a heart stopped beating, life ceased to exist. What caused the heart to beat was still a mystery.
With primate medical technologies, Romans were only able to witness the heart, in the dissected bodies of dead animals and human, thus they were never able to directly observe the heart functioning which lead to many misconceptions. Thus the heart they observed contained no blood, and when the heart had ceased to function, had pushed all the blood out of the arteries and into the veins, which bulged in a deceased animal. This lead the Romans to believe that the arteries contained only air and veins carried blood. Also, because the veins around the liver were large and bulging with blood they attributed this organ with the production of blood, a false belief that would only be corrected by Harvey in the 17th century.
During the 2nd century, the Greek physician Galen made many discoveries about the hearts function. His observed that the right side of the heart received blood from a large vein, and then this blood was ejected from the heart, to the lungs via the pulmonary artery. He also observed that this blood then returned to the heart, but this time to the left side. Galen had correctly identified the hearts main function as a pump to move blood around firstly the heart and then the body. Galen also overturned the belief that arteries contained air and discovered that they carried blood.
In order for Galen to make his discoveries he would have needed to observe the heart functioning in a living body. Galen used his observations of dying gladiators, whose chests had been ripped open by their opponent’s swords to base his discoveries on. Galen made a fatal error though, by not disclosing his subject matter in his writings. His observations were falsely attributed to describing the hearts of only animals and not humans. This meant that, for centuries, his discoveries were largely ignored by those studying the human heart.
In the 16th century, Servetus a Spanish physician both accepted and confirmed Galen’s discoveries as holding true for the human heart. He mentioned that the pulmonary artery, which carries blood from the right side of the heart to the lungs, was too large to only nourish the lungs and thus must contain all blood to the lungs, which somehow altered the composition of the blood.
Servetus other major discovery was that the heart was completely non-porous and thus the only way that blood could be transferred from the right to the left side of the heart was via the pulmonary artery and the lungs.
Servetus views on the hearts function were included in his writings about religion. He sent his writings to John Calvin, a protestant pioneer who was so horrified by his religious views that he refused to return the essay and attempted to stop its further publication. Servetus papers were still published but several months later he was arrested, tried and eventually burned at the stake with what was believed to be all of his publications.
Thankfully copies of Servetus writings survived and were to form the basis of research by Colombo and Harvey.
Colombo in the late 16th Century not only confirmed the circulation of blood by the pulmonary artery, but also made 3 other important discoveries;
1. He revealed the presence of valves in the 4 vessels that entered and exited the right and left sides of the heart. These valves allowed blood to only flow in one direction
2. He also identified and described that the heart had a contraction and relaxation phase with moved blood through the heart to the lungs and then back to the heart.
3. Lastly, he confirmed that the pulmonary artery contained no air only blood.
All of these discoveries made in prior centuries played a crucial role in Harvey’s only observations and discoveries of the heart and its function. While Harvey used many of these concepts in his own research he never acknowledged in his writings that they had already been discovered by scientists prior to him.
Harvey’s discovery is considered the most important medical discovery made by an Englishman ever, and until the publication of his book, De motu cordis (On the motion of the heart and blood) in 1628 no significant medical book had ever been published by an Englishman.
Harvey was an unusual man, who had the personality of a mad scientist, making him not a totally likeable character. He received a scholarship to Cambridge and later studied at the Royal College of Physicians and became an attending physician to James I. He then spent 12 years lecturing at the royal college of physicians about the heart, arteries and veins.
In De Motu Cordis, Harvey correctly describes the anatomy and workings of the auricles, ventricles, arteries, veins and values of the heart. He also confirmed that the values in the pulmonary artery opened and closed in such a way that it confirmed that blood was carried from the right side of the heart to the lungs. Harvey emphasised that the hearts sole function was to pump blood.
Harvey was also the first to confirm that the auricles contracted before the ventricles. Prior to Harvey no one was able to confirm this, as although they had observed a beating heart, the heart beat too fast for this process to be observed. Harvey overcame this problem in his research in two ways;
1. Firstly by observing the hearts of cold blooded animals, which beat slower than warm blooded animals
2. And secondly, by waiting for a vivisected warm-blooded animal to begin to die, during this time the hearts contractions would slow enough to be able to be observed.
Harvey also described what Servetus and Colombo had already discovered, the circulation of blood through the heart and lungs via the pulmonary artery, but he was the first to describe the process as circular. He concluded that all blood flowed in this circular manner and that once the heart ejected blood into the arteries it returned to the heart via the veins, the whole process was a complete circle.
He came to this conclusion by temporarily restricting a vein so blood couldn’t return to the heart. When he did this the heart, paled in colour and shrank in size, at the same time less blood was being ejected from the heart into the arteries. Once the vein had been restored the heart returned to its normal colour and size and blood flow into the arteries returned to normal. Thus the blood from veins returned to the heart and became the blood that flowed through the arteries. Thus he concluded that heart made blood, a miraculous discovery considering physicians still believed that blood was made by the liver.
Harvey’s only shortcoming, was his failure to notice that when blood was taken from the right side of the heart to the lungs and then returned to the left side of the heart, it changed in colour because it had been oxygenated by the lungs. It would take another 40years for this to be noted and explained. But nonetheless his discoveries have played an important part in our understanding of this vital organ and its function.
