William Harvey and the Discovery of the Human Circulatory System

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William Harvey and the Discovery of the Human Circulatory System

Overview

William Harvey (1578-1657) is recognized as the man who discovered and published the first accurate description of the human circulatory system, based on his many years of experiments and observations as a scientist and physician. Harvey had accumulated a mass of irrefutable experimental evidence in support of his dramatic new view, knowing that a tremendous amount of criticism and disbelief would be mounted against his groundbreaking, revolutionary theory of the physiology of blood circulation. Although the majority of the physicians and scientists of his day refused to accept his research, Harvey's discovery and written description of the true functioning of the heart and circulatory system remains as one of the landmark medical textbooks and the foundation of modern physiology.

Background

Most physicians, scientists, and philosophers of seventeenth-century Europe were adherents of Galen's doctrine, which contained several significant errors regarding the movement of blood and the workings of the heart. These were actually quite ancient ideas and notions, still accepted more than 1,400 years after first being postulated by Galen (130?-200?), the Greek physician of Rome. Over time, the dogma of Galen became sacrosanct, even though most of his anatomical knowledge and physiological investigations were based on his studies of monkeys and pigs, because dissections of human bodies were typically not permitted. Galen recognized the usefulness of comparative anatomy for gaining understanding of the human body, and he studied the workings of animal bodies and various structures in some detail. He was a prolific writer and dedicated scientist, venerated for centuries, and long considered to be the authority on medicine and health.

Galen and his proponents believed that the circulation of blood began in the gastric and intestinal blood vessels, and was carried to the liver, where it was "elaborated" by the liver. This "venous blood" then entered the hepatic vein, which he believed to be the origin of the vena cava, and the "descending" vena cava transported blood to the lower body, while the "ascending" branch sent blood to the upper body. As blood entered the right side of the heart, it was thought to pass through invisible pores in the septum that divided the heart, forced into the left ventricle, mixed with air brought in from the lungs by the pulmonary veins, and transformed into the "arterial blood." The heart was seen as a type of bellows, expanding when a small volume of blood in the left ventricle was greatly heated by the addition of "vital spirits," forcing the heart to expand and draw blood inside. In a similar fashion, the arteries carried this "boiled up" blood away from the heart to the body, but the blood did not return to the heart. According to Galenic doctrine, the liver was seen as the continual source of new blood, replenishing the blood that was vaporized and converted into waste material, and released from the lungs as "soot."

As the personal physician of King Charles I and the recipient of the best medical education possible, Harvey was perhaps the preeminent physician in England and perhaps all Europe, and he long doubted the accuracy of many of the "facts" that the medical profession espoused. Harvey finally published the results of his research in his text Exercitatio anatomica de motu cordis sanguinis in animalius (On the movement of the heart and blood in animals) in 1628. Harvey only accepted as facts those ideas that were supported with repeated experimental evidence, and, as was his nature, he methodically and forcefully exposed the errors of the long held misconceptions about the heart and blood circulation. His new system completely altered the Galenic concept of blood circulation, proving that the heart is a hollow muscle that contracts regularly to provide the single motive force of the blood's movement. He patiently exposed the other unacceptable aspects of Galen's erroneous system, using well-designed experiments that attempted to dispel various falsehoods.

Harvey was able to fully illustrate the actions of the heart, its chambers and valves, as well as clarify the long misunderstood pattern of pulmonary circulation. Harvey concluded that blood moved from the right ventricle into the lungs via the renamed pulmonary artery (correctly changed from pulmonary vein), which Galen thought carried only air and "soot" back and forth between the lungs and heart. Harvey properly stated that the blood then returned to the left side of the heart via the pulmonary veins. Harvey would not attempt to answer why the blood traveled to the lungs and back, as he did not have any knowledge about gas exchange during pulmonary respiration. Harvey also fully detailed the systematic circulatory system, tracing the flow of blood through the arteries coursing within the body, returning to the heart via the network of veins. He also artfully illustrated the workings of the valves in veins, proving the one-way circulation of venous blood towards the heart, and refuting the notion that the valves were actually reinforcement structures that prevented the over expansion of the veins as blood was forced through, as his university mentor Girolamo Fabrici (1537-1619) had taught.

When Harvey found that his experimental evidence could not provide an answer to a question, he did not attempt to evoke rational mysticism by way of explanation, as in the case of how and why blood in the arteries eventually passed into the veins and traveled back to the heart. Harvey could not see the capillaries found in tissues and had no way of addressing blood's metabolic function, but he did anticipate the presence of the "anastomoses" between arteries and veins and the possibility of blood providing nourishment or some other function. These blood-carrying structures were too small to be seen with the naked eye, but Harvey strongly believed that their existence would be detected eventually. Later, in the seventeenth century, both Marcello Malpighi (1628-1694) and Anton van Leeuwenhoek (1632-1723) would use the improved microscope to describe the presence of capillaries and blood cells in a wide variety of animals, including humans.

Impact

Harvey worked long and hard to create what became the starting point for modern mammalian physiology. His still impressive research is also seen as the first milestone of modern experimental science, and can be used as an example of how to perform experimental scientific research. Being the person to inaugurate two new scientific systems that condemned long-held beliefs, Galen's doctrine and the school of rationalism, Harvey must have recognized the likelihood of dire consequences. The derision and attack of the medical community was inevitable, and accusations and charges made by the Church and legal authority would not be without common precedence. New ideas that change entire systems of knowledge were always viewed with skepticism and apprehension, often evoking harsh criticisms and accusations of quackery. Harvey risked being rejected as foolishly misled or even acquiring the stigma of being labeled a quack. After his publication, his private practice suffered a great decline as a result of the intense controversy he created, but Harvey steadfastly maintained himself and his convictions during the controversy.

As a professor and physician, Harvey advocated the use of comparative techniques to study anatomy and physiology, recognizing the advantages and practicality of using the animals that were available for study. Harvey worked with fish, amphibians and reptiles, birds, mammals, and humans, experimenting and comparing where ever possible, building his theory methodically and with great care. In the case of the action of the heart, he found that in many lower animals, the heart's movement was slower and could be seen more readily, and he used the slower heart rate of chilled fish and amphibians for analysis and comparison to the faster mammalian heart. Many of Harvey's experiments would later be described as direct, artfully simple, and beautifully designed.

Throughout his career, Harvey emphasized the experimental method of scientific research, which would become a basic tenet of modern science. Harvey would not accept any rationalism or mysticism as evidence for determining how or why something occurred in the body. Only experimental evidence that was repeated many times, using as many different animal examples as possible, could be considered in reaching any conclusions. Harvey avoided having any preconceived ideas about his experiments, rather, he gathered his evidence, analyzed the data, and then created a scientific hypothesis that he knew he could further test directly with more experiments. He built his new theory of blood circulation in a straightforward analysis of each step in the process, gathering extensive experimental data to confirm every aspect. He anticipated potential criticisms and designed more experiments to refute future controversies. His reliance on the experimental method was in contrast to many scientists and philosophers of his time, who instead employed rationalism or dialectics to essentially think their way through a question or problem, often following anecdotal or casual observational information, and using little to no experimental evidence. This type of analysis typically evoked the presence of unseen forces or "principles," usually a supernatural or divine phenomenon. Harvey tended to avoid this kind of philosophical reasoning, referred to as ratiocination.

The adherents of the Galenic doctrine did not surrender to the new physiology quietly, but rather a great controversy raged for many years and long after Harvey's death. Harvey, humble and dignified as a person and in his work, was patient and understanding when dealing with his critics and doubting contemporaries. Occasionally he would answer his critics with a direct letter or a publication that would add to or reiterate the existence of the relevant experimental evidence that confirmed his conclusions. Nevertheless, recognition of the truths that he illuminated did not come in his lifetime. Eventual acceptance came much later, when scientists developed new tools of investigation and better understanding of modern science. Harvey is remembered and revered both as the founder of modern physiology and a champion of modern experimental science.

KENNETH E. BARBER