|Year : 2020 | Volume
| Issue : 3 | Page : 270-272
William harvey and the circulation: The concept, challenge, and controversy
Devender Singh, Basavarajendra Anurshetru, Aryala Shalini
Department of Vascular and Endovascular Surgery, Yashoda Hospital, Hyderabad, Telangana, India
|Date of Submission||01-Nov-2019|
|Date of Acceptance||11-Nov-2019|
|Date of Web Publication||12-Sep-2020|
Department of Vascular and Endovascular Surgery, Yashoda Hospital, Hyderabad, Telangana
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Singh D, Anurshetru B, Shalini A. William harvey and the circulation: The concept, challenge, and controversy. Indian J Vasc Endovasc Surg 2020;7:270-2
The discovery of the function of the heart and the circulation of blood by William Harvey was the greatest medical discovery of all time and is considered in the top 10 greatest discoveries in medicine. Not only did it initiate the field of physiology, but it also introduced the principle of experimentation in medicine. For his immense contribution, he is remembered as the “father of modern physiology” and the “founder of modern experimental physiology” (because his work was based on experiments on animals) [Figure 1].
William Harvey was the first in the Western world to describe correctly and in exact detail the systemic circulation and properties of blood being pumped around the body by the heart. He proposed that blood flows through the heart in two separate closed loops. One loop, pulmonary circulation, connected the circulatory system to the lungs. The second loop, systemic circulation, causes blood to flow to the vital organs and body tissue. However, this was not an easy job as he was the first scholar who dared question traditional beliefs about the heart and the circulation that dated back to Galen, 1500 years earlier. He rejected the common approach used at his time and throughout the Middle Ages, which was to rely blindly on Aristotle and Galen, accepting their theories without questions. Theories were accepted as valid just because Aristotle and Galen said so, not because they were verified empirically. Harvey, however, refused to believe uncritically what he was taught and insisted on relying not on the words of Galen, but on his own experimental observations, following his reason to its logical conclusions. This approach, which seems so obvious today, was truly revolutionary in the 17th century. Promoting critical thinking and experimental testing of ideas was, indeed, Harvey's greatest contribution to science.
All theories up to the 17th century postulated that blood was made in the liver from digested food. Blood – Galen said – leaked continuously from the liver, like water coming down from a fountain, and then went to the periphery through the veins and nourished all tissues (so, according to Galen, blood flows in the veins centrifugally, not centripetally). Galen also asserted that the tissues absorb and use all blood so that the liver has to replenish it continuously; thus, there is no circulation, no recycling of blood. According to Galen, the function of the right heart is just to nourish the lungs; it is but a different kind of “vein.” Galen further asserted that some of the venous blood finds its way from the right to the left side of the interventricular septum, through what he called “pores” (these pores were never seen, but everybody believed for 1500 years that they existed). Once the venous blood is in the left ventricle, Galen asserted, it mixes with the “pneuma,” a spiritual essence inhaled from the air in the lungs. The function of the lungs is to bring in the pneuma, which mixes with the blood and makes it become arterial; the blood is then warmed up by the innate heat of the heart, and this mixture is pushed into the arteries to the body. Again, as there is no recirculation, blood must be continually produced in the liver.
These ancient Galenic myths were demolished by Harvey in his book (1628), De Motu Cordis (the full title of the book is Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus [Anatomical Exercise About the Movement of the Heart and Blood in Animals]). This small (72 pages; 5” ×7”) monograph is one of the most important books ever written, possibly the most important book in the history of medicine (certainly, it is so for a cardiovascular scientist). It has changed the history of humankind. De Motu Cordis did for physiology what Vesalius' “Fabrica” had done for anatomy in 1543. Because of massive resistance, it was published in Frankfurt, Germany, because Harvey hoped to avoid troubles at home by publishing his findings abroad. Unfortunately, the first English translation did not appear until two decades later.
He showed that the heart fills passively and contracts actively, and that during contraction, it expels blood. Then, he showed that the expansion of the arteries (the pulse) is synchronous with, and is caused by, the contraction of the heart and by the force of the blood pushed by the heart. This seems quite obvious to us but was not understood until Harvey. Hence, Harvey's observations were a breakthrough at the time. By dissecting animals (particularly reptiles, in whom the heart rate is very slow), Harvey also showed that the atria “arouse a somnolent heart.” He also pointed out that the pulmonic and aortic valves keep blood from going back into the right and left ventricle, respectively, and the mitral and tricuspid valves keep blood from going back into the atria.
The introduction of quantitative evidence in physiology was one of the Harvey's fundamental contributions to medicine. He was the first person to actually use measurements in the studies of physiology. He asked himself: “If Galen is right – if the blood is being continuously made from food by the liver – how much blood does the liver need to make?” It is astounding that nobody actually thought to address this obvious question before. Because of his privileged position as the king's personal physician, he was allowed to study the king's deer. By looking at the hearts of animals, he estimated that each time the heart beats, it squeezes 2 ounces of blood during systole (not a bad estimate). Because the heart beats on an average 72 times/min, he calculated that 8640 ounces (or 540 pounds) of blood should be pumped per hour, which was four times the weight of an average human being at Harvey's time (though only three times today, given the current epidemic of obesity). Obviously, it was impossible for the liver to make that much blood in 1 h. These calculations led Harvey to refute the 1500-year-old Galenic idea that blood is continuously produced in the liver.
He also showed that, in the veins, the blood travels centripetally. This is another thing that now seems so obvious; one cannot help but wonder why it took 1500 years to figure out that the blood in the veins flows toward the heart, not away from it as Galen had said. Harvey's teacher, Fabricius, had described the presence of valves in the veins but had no idea what they were for. So, Harvey did the obvious experiment [Figure 2]. (He used muscular farmworkers, who had big veins.) He put a tourniquet around the arm and tried to empty the veins with his finger. He noticed that the veins would always fill from the distal to the proximal part of the arm – not vice versa, indicating that blood flows from the hand toward the shoulder. When he did the same experiment in the neck, he noticed the opposite: the blood never went from the chest to the head but, rather, from the head to the chest. He thus concluded that the blood in the veins always flowed toward the heart.
|Figure 2: A figure from De Motu Cordis illustrating the method used by Harvey to determine the direction of blood flow in the veins of the forearm|
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Harvey further concluded that the heart acted like a pump that forced blood to move throughout the body instead of the prevailing theory of his day that blood flow was caused by a sucking action of the heart and liver. These important theories of Harvey represent significant contributions to the understanding of the mechanisms of circulation.
William Harvey was born at Folkestone, Kent, England, on April 1, 1578. He received the degree of medical doctor from the University of Padua, Italy, in 1602. After his return to England, he became a Fellow of the College of Physicians, a physician to St. Bartholomew's Hospital, and a Lumleian lecturer at the College of Physicians. In 1618, Harvey was appointed physician extraordinary to James I, and he remained in close professional relations to the royal family. He died on June 3, 1657, at the age of 79. His last contribution was a book on the growth and development of the young animals entitled “De Generatione Animalium,” published in 1651.
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| References|| |
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Harvey W. On the Motion of the Heart and Blood in Animals. London: George Bell and Sons; 1889. [Last retrieved on 2016 Oct 01].
Schlesinger A. 2000. World Almanac's ten most influential people of the Second Millennium. World Almanac; 2000. [Last retrieved on 2009 Jan 28].
Harvey W. Royal Society of Medicine (Great Britain). London: Humphrey Milford, Oxford University Press; 1913. [Last retrieved on 2016 Oct 21].
[Figure 1], [Figure 2]