Über die Autorin bzw. den Autor

<p><b>Martin J. Tobin, MD</b> is Professor of Medicine, Pulmonary and Critical Care Medicine at Loyola University Health Systems in Chicago, Illinois. <p></p></p>

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Principles and Practice of Mechanical Ventilation

McGraw-Hill Companies, Inc.

Contents

Chapter One

Gene L. Colice

ANATOMISTS OF THE HEART AND LUNGS Early Greeks Renaissance Physicians

CHEMISTS AND PHYSIOLOGISTS OF THE AIR AND BLOOD Understanding Gases Metabolism Blood Gases and Ventilation

EXPLORERS AND WORKING MEN OF SUBMARINES AND BALLOONS Exploration Under Water Exploration in the Air

MECHANICAL VENTILATION OF RESUSCITATION AND ANESTHESIA Vivisection Resuscitating the Apparently Drowned Negative-Pressure Ventilators Positive-Pressure Ventilation Tracheal Intubation Tracheal Anesthesia Differential Pressure Translaryngeal Intubation For the Nonoperative Patient Modern Respirators Intensive Care Adequacy of Ventilation Quality Control of Ventilators Weaning

CONCLUSION

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.

ANATOMISTS OF THE HEART AND LUNGS

Early Greeks

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. 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.

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. 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. Aristotle described a three-chamber heart connected with passages leading in the direction of the lung, but these connections were minute and indiscernible. Presumably, the lungs cooled the blood and somehow supplied it with air.

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 that the right ventricle facilitated venous return by suction during diastole and that venous valves allowed only one-way flow of blood.

The Greek physician Claudius Galen, practicing in Rome around AD 161, demonstrated that arteries contain blood by inserting a tube into the femoral artery of a dog. Blood flow through the tube could be controlled by adjusting tension on a ligature placed around the proximal portion of the artery. He described a four-chamber heart with auricles distinct from the right and left ventricles. Galen also believed that the "power of pulsation has its origin in the heart itself" and that the "power [to contract and dilate] belongs by nature to the heart and is infused into the arteries from it." He described valves in the heart and, as did Erasistratus, recognized their essential importance in preventing the backward discharge of blood from the heart. He alluded several times to blood flowing, for example, from the body through the vena cava into the right ventricle and even made the remarkable statement that "in the entire body the arteries come together with the veins and exchange air and blood through extremely fine invisible orifices." Furthermore, Galen believed that "fuliginous wastes" were somehow discharged from the blood through the lung. Galen's appreciation that the lungs supplied some property of air to the body and discharged a waste product from the blood was the first true insight into the lung's role in ventilation. However, he failed in two critical ways to appreciate the true interaction of the heart and lungs. First, he believed, as did Aristotle and other earlier Greeks, that the left ventricle is the source of the innate heat that vitalizes the animal. Respiration in animals exists for the sake of the heart, which requires the substance of air to cool it. Expansion of the lung caused the lightest substance, that is, the outside air, to rush in and fill the bronchi. Galen provided no insight, though, into how air, or pneuma, might be drawn out from the bronchi and lungs into the heart. Second, he did not clearly describe the true circular nature of blood flow from the right ventricle through the lungs and into the left ventricle and then back to the right ventricle. His writings left the serious misconception that blood was somehow transported directly from the right to the left ventricle through the interventricular septum.

Renaissance Physicians

Byzantine and Arab scholars maintained Galen's legacy during the Dark Ages and provided a foundation for the rebirth of science during the Renaissance. Around 1550, Vesalius corrected many inaccuracies in Galen's work and even questioned Galen's concept of blood flow from the right ventricle to the left ventricle. He was skeptical about the flow of blood through the interventricular pores Galen described. Servetus, a fellow student of Vesalius in Paris, suggested that the vital spirit is elaborated both by the force of heat from the left ventricle and by a change in color of the blood to reddish yellow. This change in color "is generated in the lungs from a mixture of inspired air with elaborated subtle blood which the right ventricle of the heart communicates to the left. This communication, however, is made not through the middle wall of the heart, as is commonly believed, but by a very ingenious arrangement: the subtle blood courses through the lungs from the pulmonary...