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THE DISCOVERY OF THE PULMONARY CIRCULATION REVISITED

Ayman O. Soubani, MD; Faroque A. Khan, MB

The discovery of the pulmonary circulation is an interesting and debated subject. It is commonly believed that the discovery of the pulmonary circulation had its inception in Europe in the sixteenth century by Servetus, Vesalius, Colombo, then Harvey. However, in view of the discovery of ancient manuscripts, we propose that the real credit for the discovery of the pulmonary circulation belongs to an eminent physician of the thirteenth century: Ibn Nafis. This brief report describes the contributions made by Ibn Nafis.

Abu-Alhassan Alauldin Ali Bin Abi-Hazem Al-Quarashi, known as Ibn Nafis, was born about 1210 in Damascus. He learned medicine under the guidance of such distinguished physicians as Aldakwar and studied the books of famous pioneers as Rhazes, Avicenna and Maimonides. In 1236 Ibn Nafis moved to Egypt and worked in Al-Mansouri Hospital where he became chief of physicians and the sultan's personal physician. On December 17, 1288 he died at the age of 78 after an unknown illness.1

As with most of the Muslim physicians at that time, not only did Ibn Nafis excel in medicine but his knowledge extended to languages, philosophy, Islamic law and history. In medicine he published valuable books such as "Reference Book for Physicians, Polished Book on Ophthalmology, Commentary on Hippocrates, Epidemics, Commentary on Materia Medica and Compound Drugs". But perhaps the most important of his books was "Commentary on the Anatomy of the Canon of Avicenna", which is considered one of the best scientific books of all time, in which Nafis describes subjects in anatomy, pathology and pharma-cology. However, this book was forgotten until 1924 when an Egyptian physician, Dr. M. Altawi, discovered a script, No. 62243, titled "Commentary on the Anatomy of Canon" in the Prussian state library in Berlin while studying the history of Arab Medicine at the medical faculty of the Albert Ludwigs University in Germany.2 This discovery focused on an important scientific fact which up to then had been ignored: the first description of the pulmonary circulation.

The theory that was accepted prior to Ibn Nafis was put forth by Galen in the second century, who said that the blood reaching the right side of the heart went through invisible pores in the septum to the left side of the heart where it mixes with air to create spirit and then is distributed to the body. According to Galen's views, the venous system is quite separate from the arterial system, except when they come in contact by the unseen pores.3 However, Ibn Nafis, based on his knowdedge in anatomy and scientific thinking, postulated that "...the blood from the right chamber of the heart must arrive at the left chamber but there is no direct pathway between them. The thick septum of the heart is not perforated and does not have visible pores as some people thought or invisible pores as Galen thought. The blood from the right chamber must flow through the vena arteriosa (pulmonary artery) to the lungs, spread through its substances, be mingled there with air, pass through the arteria venosa (pulmonary vein) to reach the left chamber of the heart and there form the vital spirit...". In another site he said, "The heart has only two ventricles ...and between these two there is absolutely no opening. Also dissection gives this lie to what they said, as the septum between these two cavities is much thicker than elsewhere. The benefit of this blood (that is in the right cavity) is to go up to the lungs, mix with what is in the lungs of air, then pass through the arteria venosa to the left cavity of the two cavities of the heart ...". In describing the anatomy of the lungs, Ibn Nafis stated, "The lungs are composed of parts, one of which is the bronchi, the second, the branches of the arteria venosa and the third, the branches of the vena arteriosa, all of them connected by loose porous flesh". Then he added, "... the need of the lungs for the vena arteriosa is to transport to it the blood that has been thinned and warmed in the heart, so that what seeps through the pores of the branches of this vessel into the alveoli of the lungs may mix with what there is of air therein and combine with it, the resultant composite becoming fit to be spirit when this mixing takes place in the left cavity of the heart. The mixture is carried to the left cavity by the arteria venosa".4

Another important contribution made by Ibn Nafis that is rarely mentioned is his postulation that the nutrition of the heart is extracted from the small vessels passing through its wall, when he said "... Again his (Avicenna's) statement that the blood that is in the right side is to nourish the heart is not true at all, for the nourishment to the heart is from the blood that goes through the vessels that permeate the body of the heart...";4 by this, Ibn Nafis was the first to put forward the concept of coronary circulation.

These important observations were not known in Europe until 300 years later when some of Ibn Nafis' works were translated to Latin by Andrea Alpago of Belluno in 1547.5 After this, Michael Servetus described the pulmonary circulation in his theological book "Christianismi Restitutio" in 1553, he wrote "...air mixed with blood that is sent from the lungs to the heart through the arterial vein; therefore, the mixture is made in the lungs. The bright color is given to the sanguine spirit by the lungs, not by the heart."6 Then Andreas Vesalius described in his book "De Fabrica", the pulmonary circulation in a manner similar to Ibn Nafis' description. An interesting observation is that in the first edition of the book (1543), Vesalius agreed with Galen that the blood "... soaks plentifully through the septum from the right ventricle into the left...". Then in the second edition (1555) he omitted the above statement and wrote instead ..."I still do not see how even the smallest quantity of blood can be transfused through the substance of the septum from the right ventricle to the left...".5 Another similar description was given by Realdus Colombo in 1559 in his book "De re Anatomica".6

Then it was William Harvey who, in 1628, demonstrated by direct anatomic observation in laboratory animals the movement of blood from the right ventricle to the lung and then observed the blood returning to the left side of the heart via the pulmonary vein and again he stated that he could not find any pores in the interventricular septum. He wrote in his monograph, "Exercitatio anatomica de motu cordis et sanguinis in animalibus": "I began to think there was a sort of motion as in a circle. This I afterwards found true, that the blood is pushed by the beat of the left ventricle and distributed through the arteries to the whole body and back through the veins to the vena cava and then returned to the right auricle, just as it is sent to the lungs through the pulmonary artery from the right ventricle and returned from the lungs through the pulmonary vein to the left ventricle, as previously described."6 However, he did not understand the physiology of the pulmonary circulation - dissipation of the carbon dioxide and replacement with oxygen - which was fully elucidated by Lavoisier in the 18th century.3

It may be useful to mention the views of a few modern historians who reviewed the works of Ibn Nafis; Mieli said, "Attention has recently been called in the writings of Ibn Nafis to a description of the lesser circulation which is strangely reminiscent of the description given by Michael Servetus in the sixteenth century in his "Christianismi Restitutio". We believe that henceforth it is fair to attribute the discovery of the pulmonary circulation to Ibn Nafis who was a distant precursor of the physicians of the sixteenth century Italian School and of William Harvey who, four centuries later, described the whole of the pulmonary circulation in an accurate, clear and definitive manner".7 Max Meyrholf, a distinguished scholar of Arabic historical medicine, was struck by the resemblance of certain essential phrases in the writings of Ibn Nafis and Servetus... "It is as though the Arabic work had been translated a bit freely into Latin". And about Colombo's description..."Probably without knowledge of Servetus's book, describes the pulmonary circulation in an almost identical manner, but he adds that there are some anastomoses between the arteries and the pulmonary veins. We have seen that Ibn Nafis, three centuries before Colombo, had already noticed visible passages between the two types of pulmonary vessels".8 In the William Osler Medal Essay on the discovery of the pulmonary circulation, Edward Coppola said, "A comparison of Ibn Nafis' description with those of Valverde and Colombo reveals that there are certain striking similarities among these descriptions which seem to suggest more than a coincidental relationship...the theory of pulmonary circulation propounded by Ibn Nafis in the 13th century was not forgotten and that centuries after his death it may have influenced the direction of the anatomical investigations of Colombo and Valverde, who finally announced it to the Western world as a physiological fact susceptible to experimental proof".5

In conclusion, Ibn Nafis should be recognized as the main forerunner of Servetus, Vesalius, Colombo and Harvey in the description of pulmonary circulation as we know it today.