How William Harvey discovered blood circulation

Taken from The Wine-Dark Sea Within: a turbulent story of blood by Dhun Sethna. Copyright © 2022. Available from Basic Books, a trademark of Hachette Book Group, Inc.

The idea that blood circulates around the body. It may seem like a common notion, even an obvious one. Yet that familiar concept that the heart is an organ that pumps blood and oxygen through the arteries, with “waste” returning through the veins, took over two thousand years to develop. When it was established, it revolutionized the life sciences and ushered in modern medicine. In importance, it joins the Aristotelian Corpus which laid the foundations for the biological sciences and the Darwinian theory of natural selection. And like those ideas, its development was largely a solitary effort, conceived, initiated and completed by a single individual, the English physician William Harvey. He published the discovery of him in 1628 as a subtly titled volume Anatomy of the heart and blood inside animals (Anatomical exercise on the motion of the heart and blood in Animals), abbreviated to On the movement of the heart. Through it, Harvey not only experienced one of the greatest adventures of all time in medicine, but, in the process, he experienced the insecurity, vulnerability and frailty of the human condition. He is a man of the present; he belongs everywhere.

Blood circulation, as we now understand, is a double system. There is a circuit through the body (the systemic circulation) and one through the lungs (the pulmonary circulation). Each circuit is spoken of as a circulation because the circle is a symbol that ends at the point where it begins. The historical decay of each circulation is a theme of this book. The heart too is actually a set of two hearts that work in harmony in two different tasks. The right heart chamber pushes blood to the lungs; the left chamber distributes it to the other organs and limbs. Since the movement of life-preserving blood was crafted to be closely related to the breath of life and the maintenance of a constant body temperature, these three processes have merged to find themselves at the center of the new physiology. Hence, the purpose of this narrative is also the development of a theory of animal heat and the early physiology of respiration.

The discovery of circulation was a turning point in the history of the life sciences. He ushered in a new quantitative way of thinking that spawned further breakthroughs in disease management without which medicine, as we know it, would have been impossible. Harvey’s hydraulic description of circulating blood, founded on pumps and tubes, laid the foundation for a quantifiable mechanical system of cardiovascular physiology that led to our modern quantitative thinking in terms of blood velocity, vascular resistance, blood pressure, waves of the pulse, and so on, as well as their quantitative changes with varying pathophysiological conditions and the effects of abnormal speed and pressure on the organs of the body. If blood circulated, then new questions needed answers. What need was there for blood to perpetually circulate? What did it carry when it flowed like that and why? How and where did he get his stuff? How, where and why did he separate from it? Those responses revealed an understandable picture of the functioning of the human organism and established a physiological basis for modern medical practice.

Proper analysis of the heart’s movement as a mechanical pump, and only as a pump, which expelled blood into the vessels with each contraction was a central innovation essential to his scheme.

As a result, the mechanisms of the disease were modified and expanded. Circulation throughout the body meant that diseases could derive not only from imbalances of internal “humors”, as was believed up to the mid-nineteenth century, but also from harmful agents coming from out which could enter the bloodstream and travel to all tissues. As a corollary, some diseases could result from a “failure” of blood circulation to vital organs due to obstructions within arterial ducts, including those in the heart and brain, which have led to our understanding of how heart attacks and strokes occur. . The primary causes of disability and death remain today.

Aspects of today’s therapies, such as intravenous infusions (such as chemotherapy) or subcutaneous injections (such as insulin injections), even nasal allergy sprays, may only have been conceived after realizing that substances introduced into the bloodstream at one site, or even inhaled, they are transported to any other site because blood circulates. Routine interventions such as cardiac catheterization and stent placement within the arteries and the floating of the pacemaker and defibrillator electrodes through the veins all require one-way blood flow within the blood vessels into or from the heart chambers as described by Harvey. Life-saving support systems such as dialysis units and heart-lung machines that enable “open heart” surgeries are essentially extensions of the concept to extracorporeal circulations and cardiac assist devices (artificial hearts) that save lives during extreme acute illness or they also serve as an alternative to heart transplantation, to rely on a circulatory model. A compelling result of Harvey’s groundbreaking discovery is our current understanding of heart failure, which is our most expensive hospital diagnosis for people over the age of sixty-five. Contemporary therapy not only embraces the heart as a faulty pump, but also addresses the circulating chemical abnormalities that cause the heart muscle to deteriorate.

Scientific discovery is a complex phenomenon. The American philosopher of science Thomas Kuhn has provided what is probably the best description of him. The process, according to Kuhn, begins with recognizing an inconsistency in the normal expectations of things. An extended exploration of that anomaly follows, and the progression ends only when the new knowledge itself becomes clear. The normal state of affairs is now adapted to accommodate such learning and what Kuhn calls a “paradigm shift” takes place.

Courtesy of Basic Books

The idea of ​​a circulation was one such paradigm shift. In the case of Harvey’s circulation, the dominant system, which was the Galenic model that had prevailed unchallenged for fifteen centuries, could not be redefined but had to be replaced. The Roman physician Galen had imagined blood flowing back and forth in vessels, like an ebb and flow of tides. He had imagined two distinct vessel systems, the veins and arteries, arising from two different organs, the liver and the heart, which supplied blood to all parts of the body. Harvey’s groundbreaking discovery dispelled those outdated beliefs with new facts.

Characteristic, moreover, in the process of discovery is the progress of science by analogy, with some analogies preventing and others opening the way to truth. From the earliest times, thinkers have been fascinated by analogies to describe the realities of nature. The analogy of blood flow with the ebb and flow of Homer’s “dark-wine sea” and the Aristotelian comparison of the vascular system with an irrigation canal, as well as the analogy between life and respiration or combustion pervades the entire narrative, from Galen to Boyle. Galen invents his “natural faculty of attraction” in the body from the affinity between a magnet and iron. Empedocles in Sicily draws on the functioning of the Egyptian hourglass (water clock) to enunciate his new theory of cardiorespiratory physiology, as did Erasistrato in Alexandria from the phenomenon of horror empty (nature detests emptiness). Descartes compares fermentation in the heart chamber with wood fires. Finally, Harvey seeks solace in Aristotle’s philosophy of circles and finds confirmation of the function of the heart as a mechanical pump in Caus’s mechanical fire pump. Harvey’s work involved two simultaneous paradigm shifts: the heart’s contraction mechanism and thus blood circulation. Proper analysis of the heart’s movement as a mechanical pump, and only as a pump, which expelled blood into the vessels with each contraction was a central innovation essential to his scheme. Before Harvey, the accepted process of heart function, which came from Aristotle, was a heat-driven “fermentation” of the blood within the heart causing that organ to expand and, like “boiling milk overflowing”, caused an overflow of blood in the heart. the aorta.

The crowning glory of the discovery came during the scientific revolution of the seventeenth century, an era of “promise with disappointment and resilience with despair”. The further development of Harvey’s ideas connected a galaxy of the greatest minds and some of the strangest personalities in British science: John Locke, Christopher Wren, Robert Hooke, Henry Cavendish, Joseph Priestley and their peers; the Scot Joseph Black; the Anglo-Irish “skeptical chemist” Robert Boyle with the Oxford Chemists, as well as French Europeans René Descartes and Antoine Lavoisier. Together, they have dissolved the misconceptions of two thousand years of physiology. They, in turn, stood on the shoulders of the forgotten pioneers of the most ancient Ionic, Athenian and Alexandrian intellectual revolutions, men like Alcmeon of Crotone, Diogenes of Apollonia, Hippocrates and Praxagoras both of Cos, the Sicilian Empedocles, the Alexandrians Erofilo and Erasistrato and the Roman Galen, who all paved the way for understanding the natural world within us. Plato and Aristotle also played their significant parts. And, like everything else, it all began with Homer, with the ebb and flow of his “sea as dark as wine”.

Buy Inside the dark sea of ​​wine by Dhun Sethna here.

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