Beyond the seven bridges: gas exchange and blood supply to the lungs — a brief history of breathing
July 30, 2021
Why do we need breathing? A stupid question, because it’s already clear: to breathe. Is it butter? Nothing like that. Yes, in most languages, the words “breathe” and” breath ” are the same root and mean in general the same thing: respirer/respiration – in French; respirare/respirazione – in Italian; respirar/respiração – in Portuguese; oddychać/oddechowy – in Polish. Is it by chance that in all of Europe, only the British who drive on the left side make a distinction between “to breathe” and “respiration”? They are not always characterized by the right decisions (especially recently), but they are absolutely right in this matter. Because there is a difference, and it is of a cardinal nature. “Breathing” means simply mechanically moving a certain volume of air into and out of the lungs. But “breathing” means two things. First, the gas exchange between oxygen and carbon dioxide in the places of contact of the respiratory and circulatory systems, that is, in the alveoli. This process is called external breathing. Secondly, the assimilation of oxygen contained in the blood by cells in order to obtain energy. This is internal, or cellular, breathing. The connection between both processes was discovered only by the end of the XVIII century. So if, after reading my question at the beginning of this section, you twirled your finger at your temple, then you should know that we came to its apparent obviousness later than the US Constitution was created! And the path to this understanding was long, thorny, confusing, and sometimes comical. It ran through seven bridges.
The first bridge was overcome by the ancient Greeks.
The description of breathing, that is, drawing in air through the nose or mouth and releasing it, exists in all cultures and civilizations, all of them with one voice place breathing at the center of preserving life. Such concepts as” pneuma “in ancient Greece,” prana “in the Indian Vedas or” qi ” in Chinese Taoism are just different hypostases of the same concept. But how does breathing make it possible to maintain life? People had no idea about this for many centuries. How can this be explained? Lack of knowledge in the field of anatomy because of the ban on dissecting human corpses? Perhaps. Imperfection of research methods? And this, too.
But the main reason already at that time was the collusion of the cardiology cartel! What do I mean by that? Almost all over the world then held the opinion that the immortal human soul lives in the heart. How could anyone have thought that such a banal thing as air is of vital importance? The ancient Greeks, in particular Plato, came up with a brilliant idea: breathing is nothing more than a cooling mechanism to remove the heat produced by the heart from the body. Something like this: the heat from the heart warms the air in the body, which then goes out through the nose and mouth. Further, Plato writes: “Since there is no void where a moving body could rush, and the air we exhale tends outwards, it should be clear to everyone that it is not going into the void at all, but pushes the neighboring air out of its place; the latter in turn drives the air that will be next to it from its place, and that transmits the push further, so that all the surrounding air is moved to the place where the breath came from, and having entered there and filled it, the air follows the same path. Everything happens at the same time, like the turn of a wheel, because there is no emptiness. Therefore, the space of the chest and lungs, from where the breath came out, is again filled with air surrounding the body, which sinks into the pores of the flesh and makes its cycle, but when this air reverses and goes through the body to the outside, it becomes the culprit of a circular push that drives the breath into the passages of the mouth and nostrils.” Did you understand anything? I’m not either. It doesn’t matter. You just need to remember that when you are in front of the 67th time they will argue about whether it is possible to kill a person by covering his body with gold paint, as was done in the James Bond film “Goldfinger”, you can casually throw: “Of course”. Who said that? Plato. And this is the end of the discussion. Who will doubt the ancient Greek? The lungs are a cooling radiator! We must pay tribute to the cardiologists, they cleverly came up with everything!
It took more than 500 years before the Greek Galen, who worked as a life physician for the Roman emperor Marcus Aurelius, shook the ancient ideas about breathing with his research. So the second bridge was crossed. Galen was the first to understand the importance of the diaphragm and intercostal muscles for the mechanical process of breathing. But even he could not explain the significance of inhaled air for the rest of the body’s organs, since he did not see the connection between the lungs and the heart, and nothing was known about blood circulation at that time. It was believed that veins and arteries are two separate vascular systems from each other. Only a thousand years later, the Spanish doctor and theologian Miguel Servet thought about how the Holy Spirit takes possession of the human body. He approached the matter extremely seriously and very specifically, calling for the help of pure reason, logic and a combination of facts, as was customary in those days, because experiments were considered a product of the devil. Nevertheless, diligent reflection led him to the startling conclusion that the lungs are a suitable place for the penetration of the Holy Spirit. From there, it enters the blood and, thanks to its circulation, delivers the necessary portion of holiness to all parts of the body. Thus Servet came surprisingly close to the truth. If he had known at that time that an unknown gas called “oxygen” was acting in the form of the Holy Spirit (it was thanks to him that the bonfire on which Miguel Servet was burned burned so brightly a couple of years later), then we would have applauded him today as the first person to overcome the third bridge and describe the process of breathing for the first time. But it took more than 200 years for this to happen.
Have you ever been to Paris? If so, have you ever climbed the Eiffel Tower? Well, of course. And what did you see on the first floor just below the first platform? That’s right, frieze. The names of 72 scientists and engineers are imprinted on it. Almost all of them are French, the most outstanding minds of post-revolutionary France, contemporaries of Gustave Eiffel. On the north-western and north-eastern sides of the frieze you will see two names, the owners of which could rightfully claim that they have found a connection between the mechanism and the essence of breathing. These are the anatomist and physiologist Xavier Bichat and the chemist and naturalist Antoine Laurent Lavoisier.
Despite his short life, Bisha is considered one of the pioneers of medicine. He was the first to give a systematic description of various types of tissues (fat, muscle, connective, etc.) and realized that diseases attack the tissues, and not the organ as a whole. Bicha also concluded that arterial blood after passing through the tissues acquires the character of venous, that is, it changes color from bright red to dark red. In addition, he noticed that holding your breath also made arterial blood look like venous. Therefore, an influx of fresh air was needed to convert venous blood into arterial blood again.
Bichat’s observations and conclusions (quite correct) were based on two important discoveries made earlier. In 1628, the English physician William Harvey discovered blood circulation. From observations of the movements of the heart and the flow of blood, he concluded that blood circulates through the vessels, and is not produced in the heart, as was believed for a long time. Harvey described how the mechanical movements of the left ventricle of the heart pump blood into the arteries, which then, after passing through the organs, enters the veins and returns to the right ventricle through them. Here the process is repeated, but the blood is already flowing in a small-pulmonary-circle, which was described by the Arab doctor Ibn al-Nafis even before Harvey. Garvey and Ibn al-Nafis came to the conclusion that venous blood from the right ventricle of the heart enters the vessels of the lungs and from there returns through the arteries to the left atrium and ventricle. The fourth bridge was crossed.
But neither Ibn al-Nafis nor Harvey could answer the main question: how does blood get from the arteries to the veins and vice versa? This required the invention of the microscope and the research of the Italian Marcello Malpighi. In 1661, he first described the thinnest endings of blood vessels-capillaries-and their connection with the alveoli. Thus, Malpighi overcame the fifth bridge, opening the place where the arterial and venous circulatory systems connect. Bisha (bridge number six) skillfully supplemented the knowledge that existed at that time with his observations and made his own conclusions. Everything came together. It remains only to identify the mysterious substance in the air that provided blood recovery.
As the person who was able to overcome the seventh bridge and completely fold the picture, Providence chose the Frenchman Lavoisier. This versatile scientist, who along with chemistry and other natural sciences studied law and economics, in October 1774 met with the English theologian and chemist Joseph Priestley. He told Lavoisier about an experiment on burning mercury compounds, as a result of which he discovered an unknown substance that not only made the candle burn much brighter, but also did not allow the experimental animal sitting under a glass cap to suffocate. Lavoisier, who himself conducted various experiments with burning, was extremely interested. He repeated Priestley’s experiments and realized that he was talking about a hitherto unknown gaseous element, which he later called oxygen. Lavoisier was the first to establish that the oxygen contained in the air is consumed during respiration and carbon dioxide is formed at the same time. He went even further, studying the ratio of oxygen and carbon dioxide in the exhaled air at rest and under physical exertion. His research revolutionized: a direct link was established between the consumption of oxygen and the formation of carbon dioxide. The more oxygen was consumed under load, the more carbon dioxide was in the exhaled air. Lavoisier also found that both factors depended, among other things, on body temperature and on the composition of the food eaten. From this, he made a completely correct conclusion that respiration, in principle, is a chemical process during which food products were converted into carbon dioxide and heat (energy) with the help of oxygen. Thus, Lavoisier was the first to understand not only the essence of breathing, but also the chemical processes underlying human metabolism.
Since the publication of these discoveries and up to the present time, clarifications have been made only in a few aspects. So, the Frenchman Claude Bernard investigated the role of red blood cells in the transport of oxygen, and a little later the German doctor Felix Hoppe-Seiler explained this phenomenon by the presence of hemoglobin in them. The Dane Christian Bohr discovered how the content of oxygen and carbon dioxide in the blood affects its acidity (pH). All these discoveries still underlie the practice of treating lung diseases and are used in determining the content of various gases in the blood, exhaled air tests, stress tests and functional studies of the lungs.
So, 200 years after Servette’s theological reflections, Lavoisier exposed the ” Holy Spirit “and gave him the name”oxygen”. And although the discovery was quite in the spirit of the Enlightenment, which replaced the belief in spirits with a belief in scientific progress, it ultimately did not help Lavoisier. Like Servet, he fell victim to ideological fanatics: because of his past activities in the tax department of the old regime, in 1794 he was sentenced to death by a revolutionary tribunal and executed by guillotine. A few years later, Bisha also died. The irony of fate was that the cause of his death was pulmonary tuberculosis.