Historical Perspectives

The Common Vein Copyright 2007

Understanding the history of the lung from ancient times to the current era gives us a sense of the progress of our knowledge and a perspective of how technology can rapidly advance progress. The advent of the microscope and the development of our modern imaging tools are exemplary of how the tools have accelerated the pace of progress.   Although we can be very proud of our advancements, our history in medicine also clearly reveals our failings.  Misconceptions in one generation became truths of the next and inherited by subsequent generations to our detriment.

Most cultures even as far back as 5000 BC understood the concept of air as an element essential to life. They all had difficulty in making the essential link of functionally connecting the lungs with air. The interrelationship between the heart and the lungs was also misunderstood for many years. The heart was recognized as the central jewel of the chest, while the lungs were seen as secondary organs whose sole purpose was to serve as a coolant of the heart.

According to the Greeks, air passed through the arteries. The origin of the word artery is from the Greek “arteria” meaning “windpipe,” since they were regarded by the ancients as air ducts. This misconception arose because after death the arteries were noted to be filled with air and devoid of blood, and were therefore understood to be the conductors of air rather than of blood.

 The Egyptians in 3000 BC had a better sense of the lungs since they had to dissect the organs when the royalty were embalmed. The oldest anatomical records of the lungs date from the fragments of the Egyptian papyruses. Notable is the text of the Ebers papyrus, which originates from about 3000 years ago. During the embalming process the lungs, together with the brain, liver, and intestines, were removed and placed in four urns. The heart was left in the body because it was considered to be the seat of the soul. The ancient Egyptians were therefore very much aware of the macroscopic appearance of the lungs, but their understanding of function was limited. They taught that there were two vessels of the right ear which carried the breath of life, and two to the left ear, which carried the breath of death.

Since the Egyptians were able to get a sense of the normal macroscopic appearance of the lungs they were therefore also aware of the deranged structure of disease. Chest wall abscesses, tumors, and trauma were described in 2900 BC in the Edwin Smith Surgical Papyrus.

The theory of the four humors originated in Greek culture around 400BC and Hippocrates was a major contributor to this theory.  It was also used by Plato and Aristotle (300 BC) and subsequently by Galen. (130 -200 AD)  Humoral theory dominated the medical sciences of Greek medieval and early renaissance periods.  Through abstract and unfounded theories, the ideas of anatomy physiology, disease and behavior were developed. The misconceptions were perpetuated as truths inhibiting the progress for many generations.

The four humors phlegmatic, sanguine, melancholic, and choleric were respectively produced by the lung, liver, gallbladder and spleen.  These organs each produced a fluid: the lungs produced phlegm, while the liver produced blood, the gallbladder made black bile and the spleen was responsible for yellow bile.  These biological fluids each reflected an element with the lung representing water, the liver air, the gallbladder earth and the spleen fire.  Additionally each of the organs had special qualities.  The lungs were considered cold and moist, the liver hot and moist, the gallbladder cold and dry, and the spleen hot and dry.  The humors of each organ were thought to produce vapors which would ascend to the brain and would affect the person’s personality.  Thus the lungs were thought to produce a vapor that would manifest as a sluggish, dull, timid and fearful character.  The liver personality was happy, easy going, generous and optimistic. The gallbladder type was introspective, subject to gluttony, but also sentimental.  The splenic personality was ambitious, but short tempered, vengeful, and given to violence.  Thus the  lung reflecting the element water produced phlegm which in turn represented a cold and moist character that created a personality which was slow timid and dull.

Galen (130-200) was a Greek physician, who was the most respected physician for his generation and for many generations thereafter.  He played heavily on humoral theories.  He wrote his first treatise in about 151AD entitled “On the Movements of the Heart and Lung.”  He described the lung as having “all the properties which make for easy evacuation; for it is very soft and warm and is kept in constant motion.”  He had some understanding of the interconnectedness of the heart and lung since he stated that “blood passing through the lungs absorbed from the inhaled air, the quality of heat, which it then carried into the left heart.”   He thus understood that the purpose of inspiration was to cool the heart and that expiration was a means of ridding the body of heat.

 

Galen’s Concept of the Organs and their Faculties

Heat plays a central role part in the theory of Galen. The three ‘faculties’ of the body are the nutritive, vital and logical faculties. The nutritive faculty is related to the stomach which “cooks” the food and converts it into chyle. The chyle is transported to the liver by the portal vein. In the liver further heat converts the food into blood and adds natural spirit. Some of the blood is transported via the veins to the heart where more heat is added to create vital spirit. The blood becomes thinner is distributed to the body by the arteries giving warmth and enables growth. The vital spirit is measured through the pulse. The brain adds psychic pneuma, which provides the rational and logical faculty in the form of thought will and choice. These are distributed to the body via the nerves. The logical faculty reigns supreme and is followed in orderof importance by the vital and nutrtive faculties. The transport systems of the body include the nerves which transmit the logical faculty, the arteries which transport the vital spirit, and the veins which transport the blood with nutritive faculty from the liver. Galen faculties of the body nutrition portal vein stomach liver vein heart vital faculty pneuma lungs brain logical faculty animal spirits Davidoff art Copyright 2008 13169c18b01.8s

 

da Vinci

This drawing by da Vinci is the most exquisite pioneering effort depicting the anatomy of the human lungs. Courtesy Ashley Davidoff MD 11683

Up to the 15^th century therefore, the lungs were thought of as two fleshy masses.  There was no understanding of the details of anatomy, and there was gross misunderstanding of the physiology.

The renaissance brought in fresh blood and fresh thought.  Leonardo da Vinci in the late 15th century said, “The substance of the lung is dilatable and extensible like the tinder made from a fungus. But it is spongy and if you press it, it yields to the force which compresses it, and if the force is removed, it increases again to its original size.” Da Vinci describes the process as follows in his unpublished notebooks of the late fifteenth century:  “From the heart, impurities or ‘sooty vapors’ are carried back to the lung by way of the pulmonary artery, to be exhaled to the outer air.  His descriptions are so close to what we know and his genius continues to astound.

 

Vesalius’s (1514-1564) anatomic study allowed for a better understanding of the structural makeup of the respiratory system, and he inspired his student the Spaniard, Michael Servetus (1511-1530) who subsequently discovered the pulmonary circulation. Servetus made the bold step of straying from Galenic theory of relegating the lungs a minor role in respiration.  Servetus correctly understood that the lungs took in the air and removed the waste products from the circulation. Servetus seems to be the first person to understand respiratory function.

William Harvey (1578 -1657) made the historic step forward with his understanding of the circulation as a continuous entity that placed the arteries and veins in one system rather than in two separate systems.   His thoughts were published in De Motu Cordis (Exercitatio anatomica de motu cordis et sanguinis in animalibus [An Anatomical Treatise on the Movement of the Heart and Blood in Animals] in 1628.  William Harvey’s understanding of the circulation put the relationship of the lungs the heart and the rest of the body in the appropriate larger perspective of a circulation.

In the seventeenth century, the compound microscope was discovered. This enabled vistas to be opened in gross anatomy. Malpighi an Italian physician (1628-1694) pioneered the use of the microscope, and in 1661, four years after the death of William Harvey, identified blood in the capillaries of the lung confirming Harvey’s theory.

Antoine Laurent Lavoisier (1743-1794), a French chemist, was interested in both the anatomy and physiology of the lung, and demonstrated that oxygen was required for respiration.

In 1816 Rene T. H. Laennec, a French physician, invented the stethoscope which heralded in the science of auscultation of the lungs allowing clinicians to get a handle on changes in the breath signs.  Auscultation was the dominant diagnostic tool for clinicians for many years till the advent of lung function tests and x-rays.

On December 28th 1895Wilhelm Conrad Roentgen reported his discovery of X-rays in the Wursburg Physical Medical Society Journal.  The application of X-rays to examination of the body including the chest was very quickly adopted and adapted.  By the end of 1896, more than one thousand articles and more than fifty books were published about the roentgen ray and its application.

 

The CXR has had significant influence in the diagnosis of pulmonary diseases and it continues to be a significant tool in chest disease.  It was particularly important and helpful in the era when tuberculosis was rife.  It still serves as the most common radiological procedure though its widespread use is now being selectively channeled into fewer clinical scenarios as CT rapidly advances.  In the past the CXR was part of routine admission used as a screening technique for all patients.  This practice has been questioned and debated, and more prudent use is being employed for patients with diseases relating to the cardiopulmonary systems.  The labile ICU patient requires close radiographic monitoring.  These patients are also subject to multiple interventions including the placement of lines and tubes.  The portable CXR still plays a vital role in the ICU patient since the equipment can come to Mohammed.

Cormack and Hounsfield were awarded the Nobel prize in 1979 for their pioneering work in the development of CT scanning.  The first clinical CT scan was performed in 1974 and it took several hours to scan the head and days to reconstruct the images.  The revolution of the technique related to three major advances.  Firstly, the digital format allowed manipulation of the data.  Secondly the significant expansion of the gray scale spectrum allowed characterization of tissue that was not previously possible.  For example it allowed the distinction between gray and white matter of the brain.   This expanded gray scale also gave us an unprecedented window into the lung parenchyma and interstitium.   Thirdly imaging in the axial plane provided an improved perspective of the bodily structures with unparalleled clarity.

Over the recent few years the development of slip ring technology together with the advance of multiple detector technology lead to a reduction in scan times with resultant reduction in motion artifact and improved temporal resolution.  High resolution imaging of the lung parenchyma and pulmonary arterial CT angiography have benefited significantly from this technology.

Technology is rapidly advancing to reveal the secrets of nature while the structure of nature itself is relatively unchanging. One can therefore never regret detailed study of anatomy since once learned and remembered it will not be subject to change in the way that technology will change.