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The history of mechanical ventilation is intimately intertwined with the history of anatomy, chemistry, and physiology; exploration under water and in the air; and of course, modern medicine. Anatomists described the structural connections of the lungs to the heart and vasculature and developed the earliest insights into the functional relationships of these organs. They emphasized the role of the lungs in bringing air into the body and probably expelling waste products, but showed little understanding of how air was used by the body. Chemists defined the constituents of air and explained the metabolic processes by which the cells used oxygen and produced carbon dioxide. Physiologists complemented these studies by exploring the relationships between levels of oxygen and carbon dioxide in the blood and ventilation. Explorers tested the true limits of physiology. Travel in the air and under water exposed humans to extremes in ventilatory demands and prompted the development of mechanical adjuncts to ventilation. Following the various historical threads provided by the anatomists, chemists, physiologists, and explorers provides a useful perspective on the tapestry of a technique modern physicians accept casually: mechanical ventilation.
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Early Greek physicians endorsed Empedocles’ view that all matter was composed of four essential elements: earth, air, fire, and water. Each of these elements had primary qualities of heat, cold, moisture, and dryness.1 Empedocles applied this global philosophic view to the human body by stating that “innate heat,” or the soul, was distributed from the heart via the blood to various parts of the body.
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The Hippocratic corpus stated that the purpose of respiration was to cool the heart. Air was thought to be pumped by the atria from the lungs to the right ventricle via the pulmonary artery and to the left ventricle through the pulmonary vein.2 Aristotle believed that blood was an indispensable part of animals but that blood was found only in veins. Arteries, in contrast, contained only air. This conclusion probably was based on his methods of sacrificing animals. The animals were starved, to better define their vessels, and then strangled. During strangulation, blood pools in the right side of the heart and venous circulation, leaving the left side of the heart and arteries empty.2 Aristotle described a three-chamber heart connected with passages leading in the direction of the lung, but these connections were minute and indiscernible.3 Presumably, the lungs cooled the blood and somehow supplied it with air.4
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Erasistratus (born around 300 BC) believed that air taken in by the lungs was transferred via the pulmonary artery to the left ventricle. Within the left ventricle, air was transformed into pneuma zotikon, or the “vital spirit,” and was distributed through air-filled arteries to various parts of the body. The pneuma zotikon carried to the brain was secondarily changed to the pneuma psychikon (“animal spirit”). This animal spirit was transmitted to the muscles by the hollow nerves. Erasistratus understood ...