For more than 1400 years, Galen's concept of cardiovascular anatomy, blood motion and humoral theory of disease had prevailed in Europe. Claudius Galen (AD 130-200) is considered the last great Greek physician and philosopher of the antiquity. He believed in the concept of "pneuma" or "spirit" and described three distinct types: pneuma physicon or natural spirit that was created in the liver, pneuma zoticon or vital spirit that was generated in the left ventricle, and pneuma psychicon or animal spirit which was the true substance of the soul and created in the brain.
According to Galen, after the ingestion of food, the latter was transformed into chyle and transported from the intestine to the liver via the portal vein. Then the blood was formed in the liver, mixed with the natural spirit and transported to the whole body for nutrition through the veins. The liver was regarded by Galen as the center of the venous system. The nutritive blood was thought to ebb and flow, up and down in the veins. During this movement, the impurities were also extracted from various organs of the body and brought into the venous system. Part of the venous blood was transported from the liver via the vena cava to the right ventricle. A major function of the lungs and the heart was to clean the blood from its impurity. That function was accomplished by the transport of the blood through the pulmonary artery during the expiratory phase of respiration. This purified blood ebbed to and fro within the venous system for nutritional purposes.
A small portion of the right ventricular blood was passed to the left ventricle through small and invisibles pores in the interventricular septum. During the same time, the air was transported from the lungs via the pulmonary veins to the left ventricle. In the left ventricle, the blood and air were mixed forming "vital spirit" which was then conveyed to the entire body via the arterial system. In his description, Galen adhered to the ebb and flow motion of the blood and did not visualize its circulatory movement. Galen believed that the vital spirits were responsible for all types of muscular activity and movements. He considered the heart as primarily an organ of respiration and the production of animal heat and the lungs as a cooling bath to the heart.
From anatomic point of view, he considered the heart as a two-chamber structure. The right and left atria were described as reservoir chambers and were not an integral component of the heart. According to Galen's theory of blood motion, cardiac valves and the mitral valve to a greater extent were incompetent. As described above, the air was transported from the lungs to the left ventricle through the pulmonary veins and the mitral valve. Once the blood and air were mixed to form the vital spirit, the latter was transported either through the aorta and arterial system to the body or from the heart to the lungs via the mitral valve to expel the "sooty vapours" which the natural heat had produced in that organ. According to Galen, the greater incompetency of the mitral valve was due to the fact it was composed of two membranes (leaflets) whereas the tricuspid and semilunar valves were composed of three membranes. As we will see Harvey who discovered the blood circulation in 1628 rejected strongly this theory.
Galen's humoral theory of disease was based on the concept that disease resulted from an imbalance between the four humors which were blood, phlegm, yellow bile and black bile. They were directly linked to four elements of fire, water, air, and earth respectively. This aberrant concept therefore ignored the anatomic structural changes that could affect negatively an organ function as well as abnormal physiologic conditions that could lead to an end organ dysfunction.
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