William Harvery was an English physician and studied medicine at the very famous University of Padua. He was a pupil of Fabricius. Harvery described for the first time in "De motu cordis" the exact circulation of the blood through the lungs and the entire body in 1628. For most historians the discovery of the blood circulation is one of the greatest scientific achievements of all time. Because of his genius and the fundamental character of his discovery, Harvey is the most celebrated physician in the history of medical sciences.
De motu cordis is considered the most important publication in the history of medicine. It is a very logical and well-organized book, written in a concise manner with only 72 pages divided into 17 chapters. The entire book is based on Harvey's personal observations and animal experimentations, founding the field of experimental physiology.
In the introduction of his monograph, Harvey described the weakness of previous observations on the motion of the blood and questionned Galenic theory particularly with respect to right ventricular function, the existence of invisible pores in the septum and the mitral valve function:
"Why, I ask, when we see that the structure of both ventricles is almost identical, there being the same apparatus of fibres, and braces, and valves, and vessels, and auricles, and both in the same way in our dissections are found to be filled up with blood similarly black in colour, and coagulated- why, I say, should their uses be imagined to be different, when the action, motion, and pulse of both are the same? If the three tricuspid valves placed at the entrance into the right ventricle prove obstacles to the reflux of the blood into the vena cava, and if the three semilunar valves which are situated at the commencement of the pulmonary artery be there, that they may prevent the return of the blood into the ventricle; why, when we find similar structures in connexion with the left ventricle, should we deny that they are there for the same end, of preventing here the egress, there the regurgitation, of the blood?"
Regarding the mitral valve he noted:
"When it is said that the left ventricle draws materials for the formation of spirits, air and blood, from the lungs and right sinuses of the heart, and in like manner sends spirituous blood into the aorta, drawing fuliginous vapours from there, and sending them by the pulmonary vein into the lungs,whence spirits are at the same time obtained for transmission into the aorta, I ask how, and by what means is the separation effected? And how comes it that spirits and fuliginous vapours can pass hither and thither without admixture or confusion? If the mitral cuspidate valves do not prevent the egress of fuliginous vapours to the lungs, how should they oppose the escape of air? And how should the semilunars hinder the regress of spirits from the aorta upon each supervening diastole of the heart? Above all, how can they say that the spirituous blood is sent from the pulmonary veins by the left ventricle into the lungs without any obstacle to its passage from the mitral valves, when they have previously asserted that the air entered by the same vessel from the lungs into the left ventricle, and have brought forward these same mitral valves as obstacles to its retrogression? Good God! how should the mitral valves prevent the regurgitation of air and not of blood?"
The first part of the Harvey's treatise deals with the movements of the heart whereas the second part focuses on the circulation of the blood. In the first part, Harvey described the movements of systole and diastole, the arterial pulse and the movements of the atria. He then considered the heart as a pump, forcing blood round the body:
"... the chief function of the heart is the transmission and pumping of the blood through the arteries to the extremities of the body. Thus the pulse which we feel in the arteries is nothing else than the impact of blood from the heart."
Harvey also showed that left and right ventricular contraction during systole propel the blood to the aorta and pulmonary artery respectively and again contradicted another Galenic teaching according to which active arterial dilatation attracted blood from the heart.
He strongly opposed the Galenic idea of invisible pores in the interventricular septum allowing the passage of blood from the right to left ventricle:
"...in the more perfect warm-blooded adult animals, as man, the blood passes from the right ventricle of the heart through the pulmonary artery to the lungs, from there through the pulmonary veins into the left auricle, and then into the left ventricle."
During his experimentation, Harvey placed emphasis on a quantitative measurement with mathematical reasoning and volume calculations of the amount of blood that was circulating through the heart:
"...If the heart in one beat in man, the sheep, or the ox, emits one drachim, and there are as thousand beats in half an hour, ten pounds five ounces have been transmitted in the same time ; if in one beat it emits two drachms, the total is twenty pounds ten ounces ; if in one beat half an ounce, the total is forty one pounds eight ounces ; finally , if it is an ounce at each beat, eighty three pounds four ounces have been transfused in half an hour from the veins into the arteries..."
This quantitative analysis clearly showed that the Galenic concept of blood being constantly produced by liver was incorrect and that the blood was flowing in a closed circuit throughout the body. Once for all Harvey demonstrated that the center of cardiovascular system was the heart and not liver as suggested by Galen.
The inevitability of blood circulation from this quatitative approach was reinforced by further evidence such as venous valves and the results of ligation that indicated unidirectional blood flow. Harvery demonstrated that after the placement of a tight ligature on the arm, the arterial pulse below it disappears, the veins become empty and the hand cool. Once the ligature is removed, the veins become distended and swollen and the arterial pulse reappears. He noted that the presence of the valves in the veins allows the blood to flow in one direction toward the heart and that a probe can not be inserted into a vein away from the heart. All these experimentations led Harvey to conclude:
"It is obvious that blood enters a limb through the arteries and returns through the veins, that the arteries are the vessels carrying blood from the heart and the veins the channels returning it to the heart."
Although Harvey described the passage of the blood from the arterial to the venous system, he was unable to show the exact nature of this communication. This demonstration was achieved by Marcello Malpighi who observed the capillary system under magnifying lenses in 1661.
Harvey's theory of blood circulation was debated for several decades raising huge amount of controversies as it was challenging Galenic teaching. It was gradually accepted during his lifetime as the convincing power of logic and reproducible experimentation was greater than that of superstition.
William Harvey. Exercitatio anatomica de motu cordis et sanguinis in animalibus. English translation with annotations by C.D. leake. London, 1928
Willam Harvey. The works of William Harvey. Translated by Robert Willis, London ,Sydenham society publication, 1847
William Harvey. On the motion of the heart and blood in animals. Translated by Robert Willis, Harvard Classics, Collier , 1938
Willius FA, Dry TJ. A history of the heart and the circulation. Philadelphia, W.B. Saunders, 1948
Silverman ME. Profiles in cardiology: William Harvery and the discovery of the circulation of blood. Clin Cardiol 1985;8:244-246