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The Discovery of Circulation

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Vincent Valentine, MD
University of Alabama Birmingham
Birmingham, AL, USA

As you recall, modern science emerged in the 17th century with the scientific revolution and was largely based on skepticism. This same skepticism motivated Andreas Vesalius, the father of modern anatomy, in the 16th century. Among other things, it was William Harvey who reintroduced the notion of experimentation by basing his theories on human dissections and observations he made himself. Galen had originally introduced experimentation through his research; however, he dissected and observed animals rather than the human body. Also recollected from Galen were his philosophical contributions to medicine involving humoral imbalance, which lasted until Harvey's discovery of circulation.

Like Andreas Vesalius, William Harvey studied medicine at the University of Padua, where he absorbed the spirit of free inquiry and intellectual independence that characterized Italian universities during the Renaissance. Having a restless and skeptical nature, Harvey was dissatisfied with the old Galenic concept that organs received nutrition by a process of drenching, in which blood ebbs and flows to the organs through large veins originating in the liver, the site at which blood was thought to be manufactured to fill the needs of each outpouring. To test his suspicion, Harvey created a series of ingenious experiments and measurements that demonstrated the heart's function as a pump, which as he described it in 1628, ensures that "the blood in the animal body moves around in a circle continuously." Harvey's discovery of circulation was the product of the curiosity and expansive thought characterizing the Scientific Revolution of the illuminating 17th century, a time when the likes of Galileo, Newton, van Leeuwenhoek, Halley, Descartes, Bacon, Hooke and Bernoulli were tested to establish the basis of modern observational and experimental research.

Before proceeding on with Harvey's discovery, let's summarize the current theories of blood flow before he started his work. According to Galen's theory, after swallowed food entered the stomach it was processed and passed through the "portal vein" into the liver to produce blood. The blood would then exit the liver through large veins into the vena cava. The vena cava came from the heart, which propelled the blood all over the body such that all tissues were drenched with it. It was believed that pneuma, the ethereal stuff, was a vital principle in the air that was constantly inhaled into the lungs then transported to the left side of the heart, the left ventricle. The pneuma was mixed with the blood and delivered to the rest of the body through the arteries, giving the blood a bright red appearance, whereas nutritional blood was believed to be dark. Although It was never understood how the blood returned and passed the flowing blood to the tissues, this concept was accepted and persisted for nearly 1500 years.

This brings us to Harvey, the very talented physician with an outstanding practice that kept growing When eventually, he became the doctor for royalty and nobility. James I, Charles I and the Lord Chancellor Sir Francis Bacon were among his patients. Around the time of Shakespeare's death, Harvey was appointed to the Lumleian lectureship for the Royal College of Physicians. For these lectures, he was asked to present new knowledge. It was during this time that he was intent on studying how the heart beats. Years of his work were presented in these Lumleian lectures which comprised the first seven chapters of his book Exercitatio Anatomica de Motu Cordis et Sanguis in Animalibus, Anatomical Studies on the Motion of the Heart and of the Blood in Animals, and as we know it today...de Motu Cordis.

His first observation was the clenching thrusting motion of the heart, systole. He was able to show that blood actually returns to the heart via the "vena cavae" and enters the right atrium. While it returns from the lungs, blood enters the left atrium via the pulmonary veins. From the atria, blood cascades down into the ventricles, then at the very last instant, in the wink of an eye, both atria contract followed immediately by ventricular contraction ejecting blood into the lungs and the rest of the body. As he had written so beautifully, "the atria arouse the somnolent heart."

But he remained confused about the large quantity of blood drenching the tissues with so little returning. He measured that the human cadaver heart held only 60 cc of water and that it beats 72 times a minute. The result over the course of an hour the heart would pump over 500 lbs of blood. "The only way he can explain all of this blood pumping out of the heart is if it's the same blood, and it keeps coming back. We just can't make that much." As an aside, it was Harvey's teacher, the great professor of anatomy at the University of Padua who had discovered valves in the veins. Fabricius didn't know what the valves did because blood was traveling to the periphery; therefore, he concluded their function was to slow the blood down. It was Harvey who determined that blood in the arms travels from the periphery to the center, and that the purpose of the valves was to keep blood from regurgitating back. Consequently, he wrote in Chapter Eight of his book:

I ponder often and deeply these matters. For a long time, I turned over in my mind such questions as how much blood is transmitted, how short a time its passage takes, not deeming it possible for food mass to furnish such an abundance of food, unless it somehow got back to the veins from the arteries, and returned to the ventricles. I began to think there had to be some sort of motion as in a circle.

It was in Chapter 14 where he wrote: "It must therefore be concluded that the blood in the animal body moves about in a circle, continuously, and that the action or function of the heart is to accomplish this by pumping. This is the only reason for the motion and the beat of the heart." By this point, Harvey understood the blood was being carried out through the arteries and back to the heart through the veins. The heart provided the motion by its pumping action, but how did the blood move from the most peripheral arteries into the most peripheral veins? He postulated a passageway between the arteries and the veins. Then 32 years later, Marcello Malphighi showed capillaries carrying blood from the most peripheral end arteries into the end veins.

Harvey was the first physician to use the scientific method and apply the principles of inductive reasoning, yet interestingly uninfluenced by his patient, Sir Francis Bacon. It was Vesalius and Harvey who moved us from the "age of the ear," where people listen to authority and learned only from authority to the "age of the eye," where one had to see for oneself and prove to others what you said was true.

Harvey leaves us with his most enduring quote on inductive reasoning, "Nature herself must be our adviser. The path she chalks must be our walk, for as long as we confer with our own eyes, and make our assent from lesser things to higher, we shall be at length received into her closet secrets." ■

Disclosure Statement: The author has no conflicts of interest to disclose.

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