The pulmonary circulation is archaically known as the "lesser circulation" which is still used in non-English literature. The discovery of the pulmonary circulation has been attributed to many scientists with credit distributed in varying ratios by varying sources. In much of modern medical literature, the discovery is credited to English physician
William Harvey (1578 – 1657 CE) based on the comprehensive completeness and correctness of his model, despite its relative recency. Other sources credit one or more of Greek philosopher
Hippocrates (460 – 370 BCE), Arab physician
Ibn al-Nafis (1213 – 1288 CE), Syrian physician
Qusta ibn Luqa or Spanish physician
Michael Servetus (c. 1509 – 1553 CE). Several figures such as Hippocrates and al-Nafis receive credit for accurately predicting or developing specific elements of the modern model of pulmonary circulation: Hippocrates for being the first to describe pulmonary circulation as a discrete system separable from systemic circulation as a whole and al-Nafis The
Edwin Smith Papyrus (1700 BCE), named for American Egyptologist
Edwin Smith (1822 – 1906 CE) who purchased the scroll in 1862, provided evidence that Egyptians believed that the heartbeat created a pulse that transported the above substances throughout the body. A second scroll, the
Ebers Papyrus (c. 1550 BCE), also emphasized the importance of the heart and its connection to vessels throughout the body and described methods to detect cardiac disease through pulse abnormalities. Although they had knowledge of the heartbeat, vessels, and pulse, the Egyptians attributed the movement of substances through the vessels to air that resided in these channels, rather than to the heart's exertion of pressure. The Egyptians knew that air played an important role in circulation but did not yet have a conception of the role of the lungs. The next addition to the historical understanding of pulmonary circulation arrived with the Ancient Greeks. Physician
Alcmaeon (520 – 450 BCE) proposed that the brain, not the heart, was the connection point for all of the vessels in the body. He believed that the function of these vessels was to bring the "spirit" ("
pneuma") and air to the brain.
Empedocles (492 – 432 BCE), a philosopher, proposed a series of pipes, impermeable to blood but continuous with blood vessels, that carried the pneuma throughout the body. He proposed that this spirit was internalized by pulmonary respiration. He wrote that the right ventricle played a different role to the left: it transported blood to the lungs where the impurities were vented out so that clean blood could be distributed throughout the body. Though Galen's description of the anatomy of the heart was more complete than those of his predecessors, it included several mistakes. Most notably, Galen believed that blood flowed between the two ventricles of the heart through small, invisible pores in the interventricular septum. However, Avicenna's description of pulmonary circulation reflected the incorrect views of Galen. The Arab physician, Ibn al-Nafis, wrote the
Commentary on Anatomy in ''Avicenna's Canon'' in 1242 in which he provided possibly the first known description of the system that remains substantially congruent with modern understandings, in spite of its flaws. Ibn al-Nafis made two key improvements on Galen's ideas. First, he disproved the existence of the pores in the interventricular septum that Galen had believed allowed blood to flow between the left and right ventricles. Second, he surmised that the only way for blood to get from the right to the left ventricle in the absence of interventricular pores was a system like pulmonary circulation. He also described the anatomy of the lungs in clear and basically correct detail, which his predecessors had not. However, like Aristotle and Galen, al-Nafis still believed in the quasi-mythical concept of vital spirit and that it was formed in the left ventricle from a mixture of blood and air. Despite the enormity of Ibn al-Nafis's improvements on the theories that preceded him, his commentary on
The Canon was not widely known to Western scholars until the manuscript was discovered in
Berlin,
Germany, in 1924. As a result, the ongoing debate among Western scholars as to how credit for the discovery should be apportioned failed to include Ibn al-Nafis until, at earliest, the mid-20th century (shortly after which he came to enjoy a share of this credit). In 2021, several researchers described a text predating the work of al-Nafis,
fargh- beyn-roh va nafs, in which there is a comparable report on pulmonary circulation. The researchers argue that its author, Qusta ibn Luqa, is the best candidate for the discoverer of pulmonary circulation on a similar basis to arguments in favour of al-Nafis generally. It took centuries for other scientists and physicians to reach conclusions that were similar to and then more accurate than those of al-Nafis and ibn Luqa. This later progress, constituting the gap between medieval and modern understanding, occurred throughout Europe. Italian polymath
Leonardo da Vinci (1452 – 1519 CE) was one of the first to propose that the heart was just a muscle, rather than a vessel of spirits and air, but he still subscribed to Galen's ideas of circulation and defended the existence of interventricular pores. The Flemish physician
Andreas Vesalius (1514 – 1564 CE) published corrections to Galen's view of circulatory anatomy, questioning the existence of interventricular pores, in his book
De humani corporis fabrica libri septem in 1543. Spanish
Michael Servetus, after him, was the first European physician to accurately describe pulmonary circulation. His assertions largely matched those of al-Nafis. In subsequent centuries, he has frequently been credited with the discovery, but some historians have propounded the idea that he potentially had access to Ibn al-Nafis's work while writing his own texts. Servetus published his findings in
Christianismi Restituto (1553): a theological work that was considered heretical by Catholics and Calvinists alike. As a result, both book and author were burned at the stake and only a few copies of his work survived. Italian physician
Realdo Colombo (c. 1515 – 1559 CE) published a book,
De re anatomica libri XV, in 1559 that accurately described pulmonary circulation. It is still a matter of debate among historians as to whether Colombo reached his conclusions alone or based them to an unknown degree on the works of al-Nafis and Servetus. Finally, in 1628, the influential British physician
William Harvey (1578 – 1657 AD) provided at the time the most complete and accurate description of pulmonary circulation of any scholar worldwide in his treatise
Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus. At the macroscopic level, his model is still recognizable in and reconcilable with modern understandings of pulmonary circulation. ==References==