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The animals were starved, to better define was somehow transported directly from the right to the left their vessels, and then strangled. During strangulation, ventricle through the interventricular septum. He was skeptical about was distributed through air-filled arteries to various parts the flow of blood through the interventricular pores Galen of the body. The pneuma zotikon carried to the brain was described. This animal spirit was transmitted to the muscles the force of heat from the left ventricle and by a change in by the hollow nerves.
Erasistratus understood that the color of the blood to reddish yellow. This communication, The Greek physician Claudius Galen, practicing in however, is made not through the middle wall of the heart, Rome around ad , demonstrated that arteries contain as is commonly believed, but by a very ingenious arrange- blood by inserting a tube into the femoral artery of a dog. During this passage the blood is mixed with inspired tion of the artery.
He described a four-chamber heart with air and through expiration it is cleansed of its sooty vapors. He further advanced the the entire body the arteries come together with the veins concept of circulation by noting that the left ventricle dis- and exchange air and blood through extremely fine invis- tributes blood to the body through the aorta, blood returns ible orifices. However, he failed in two critical ways to pulse, action, use and usefulness of the heart and arteries.
First, He questioned why the left ventricle and right ventricle he believed, as did Aristotle and other earlier Greeks, that traditionally were felt to play such fundamentally different the left ventricle is the source of the innate heat that vital- roles. If the right ventricle existed simply to nourish the izes the animal. Respiration in animals exists for the sake lungs, why was its structure so similar to that of the left of the heart, which requires the substance of air to cool it.
Furthermore, when one directly observed the Expansion of the lung caused the lightest substance, that is, beating heart in animals, it was clear that the function of the outside air, to rush in and fill the bronchi. Galen pro- both right and left ventricles also was similar.
In both cases, vided no insight, though, into how air, or pneuma, might when the ventricle contracted, it expelled blood, and when be drawn out from the bronchi and lungs into the heart. The motion of the auricles preceded the lungs.
In the lungs the blood took up some substance, that of the ventricles. Indeed, the motions are consecu- evidenced by the change in color observed as blood passes tive with a rhythm about them, the auricles contracting through the pulmonary circulation. The site of this in turn, contracting and forcing blood into the arteries. What changed the color of blood and was cannot do otherwise than flow through continuously.
Thus, the right ventricle may be where did this combustion occur, in the left ventricle as said to be made for the sake of transmitting blood through supposed from the earliest Greek physician-philosophers the lungs, not for nourishing them. If blood were a carrier, pumped by the the quantity of blood pumped by the heart.
If the heart left ventricle to the body, what was it carrying to the tissues pumped 1 to 2 drams of blood per beat and beat times and then again back to the heart?
Clearly, the body could not produce amounts of cal reaction. Where else could to be similar to the gas produced by fermentation. This grotto was notorious for containing say, then blood must be only a carrier of critical nutrients air that would kill dogs but spare their taller masters. Presumably, the problem of the elimination gas, of course, was carbon dioxide.
In the late seventeenth of waste vapors from the lungs also was explained by the century, Boyle recognized that there is some substance in idea of blood as the carrier. Place a flame in a bell jar, and the flame eventually between the lungs and the heart and the role of blood were will go out. Place an animal in such a chamber, and the finally understood. Only two steps remained for the anat- animal eventually will die. If another animal is placed in omists to resolve. First, the nature of the tiny pores and that same chamber soon thereafter, it will die suddenly.
If the found that air passes via the trachea and bronchi into bell jar were covered by a moistened bladder, the bladder and out of microscopic saccules with no clear connec- bulged inward when the mouse died.
Obviously, the ani- tion to the bloodstream. He further described capillaries: mals needed something in air for survival. Air the basis of muscular contraction. Evidence supporting this dissolved in liquids could pass through membranes with- concept came indirectly.
In the early s, the concept of out pores. Air and blood finally had been linked in a plau- air pressure was first understood. Apparently Hooke favored dramatic experiments, and he Understanding Gases often demonstrated in front of crowds that small animals died after air was evacuated from the chamber. Hooke actu- The anatomists had identified an entirely new set of prob- ally built a human-sized chamber in and volunteered lems for chemists and physiologists to consider.
The right to enter it. Fortunately, the pump effectively removed only ventricle pumped blood through the pulmonary artery to about a quarter of the air, and Hooke survived.
The jar 6 contains an animal in this illustration. Pressure is lowered in the jar by raising the tightly fitting slide 5 with the crank 4. Used, with permission, from Graubard.
This device enabled him to collect gases produced by heating. On the top is a closed-circuit respiratory believed that the difficulty encountered in breathing under apparatus for inhaling the collected gases. Used, with permission, from these conditions was caused solely by the loss of elastic- Perkins.
He went on to observe, however, that animal blood bubbled when placed in a vacuum. This observation clearly showed that blood contained a gas of some type. In with a liquid. In a Scottish church where a large The first constituent of air to be truly recognized was congregation gathered for religious devotions, he allowed carbon dioxide.
Joseph Black, around , found that lime water to drip over rags in the air ducts. After the ser- limestone was transformed into caustic lime and lost weight vice, which lasted about 10 hours, he found a precipitate of on being heated.
The same results was produced during the services. He called the lib- would extinguish flame and life. The gas released in this process passed through the long neck of a flask and was isolated over mercury. This gas allowed a flame to burn brighter and a mouse to live lon- ger than in ordinary air.
Like Priestley, Scheele found that the gas iso- lated made a flame burn brighter. Priestley and Scheele described their observations to Antoine Lavoisier. Further work led Lavoisier to the conclusion that ordinary air must have at least two sepa- rate components.
One part was respirable, combined with metals during heating, and supported combustion. The other part was nonrespirable. Lavoisier realized that oxygen was the explanation for combustion. FIGURE The ice calorimeter, designed by Lavoisier and Laplace, Metabolism allowed these French scientists to measure the oxygen consumed by an animal and the heat produced by that same animal.
With careful mea- surements, the internal combustion of animals was found to be similar, In the s, Lavoisier performed a brilliant series of stud- in terms of oxygen consumption and heat production, to open fires. Lavoisier knew that oxygen was essen- tial for combustion and necessary for life. Furthermore, he was well aware of the Greek concept of internal heat pre- sumably produced by the left ventricle. The obvious ques- level to the tissues, and there formed the basis for the for- tion was whether animals used oxygen for some type of mation of carbon dioxide.
Would this internal combustion be perfected a closed-circuit metabolic chamber with devices similar to that readily perceived by the burning of coal? Pettenkofer built a closed- ice calorimeter Fig. This device could do two things. In and barium hydroxide to collect carbon dioxide. Although addition, the consumption of oxygen could be measured.
As Lavoisier suspected, the ods of controlled ventilation. In , Lower placed a cork in the trachea of dioxide. Removing the cork and ventilating the lungs in arterial blood than in venous blood but higher carbon with a bellows made the arterial blood bright red again. He Lower felt that the blood must take in air during its course believed that inhaled oxygen was absorbed into the blood, through the lungs and therefore owed its bright color transported throughout the body, given off at the capillary entirely to an admixture of air.
FIGURE Regnault and Reiset developed a closed-circuit metabolic chamber in for studying oxy- gen consumption and carbon dioxide production in animals. Used, with permission, from Perkins. This huge device, constructed by Pettenkoffer, was large enough for a person.
The actual chamber. The gas meters used to measure gas volumes are shown next to the chamber. The steam engine and gasometers for circulating air are labeled A. A close-up view of the gas-absorbing device adjacent to the gas meter in B. With this device Pettenkoffer and Voit studied the effect of diet on the respi- ratory quotient. The subject exhaled through the mouthpiece at the right.
Carbon dioxide extracted by means At the end of expiration, the stopcock on the accessory collecting of the vacuum was quantified by the change in weight of bag was opened, and a small aliquot of air was trapped in this device. Hence, the variables determining laboratory the arterial partial pressure of oxygen was gas content in blood were presumed to be the absorption thought to be approximately 20 mm Hg.
The partial pres- coefficients and partial pressures of the gases. In the s, sure of carbon dioxide reportedly was much higher. These Meyer and Fernet showed that the gas content of blood was results could not entirely support the concept of passive determined by more than just simple physical properties. Ludwig and others suspected that an relatively stable despite large fluctuations in its partial active secretory process was involved in gas transport. Paul Bert proposed that oxygen consumption could The gas composition in those swim bladders seemed to not strictly depend on the physical properties of oxygen be different than that of atmospheric air.
Biot concluded dissolving under pressure in the blood. As an example, that gas was actively secreted into these bladders. Oxygen consumption could be maintained with far more accurate device for measuring gas tensions than the sudden changes in pressure only if chemical reactions that used by Ludwig. When they obstructed a bronchus, contributed to the oxygen-carrying capacity of blood.
They concluded that the sure. Hoppe-Seyler was instrumental in attributing the lung did not rely on active processes for transporting oxy- oxygen-carrying capacity of the blood to hemoglobin. Using a bellows time, Bohr resurrected this controversy. With his wife, Krogh In , Miescher-Rusch demonstrated that carbon diox- convincingly showed that alveolar air oxygen tension ide excess was the more potent stimulus for ventilation.
Even small changes in alveolar cable only to people at rest. Perhaps during the stress of carbon dioxide fraction greatly increased minute ventila- either exercise or high-altitude exposure, passive diffusion tion, but hypoxia did not increase minute ventilation until might not be sufficient.
Possibly carbon diox- ide tensions led to widely divergent results. B gas released from the lungs. The exchange of oxygen and carbon dioxide between air and blood was determined by the tensions of these gases and simple passive diffusion. Blood was a carrier of these two gases, as Harvey first sug- gested. Oxygen was carried in two ways, both dissolved in plasma and chemically combined with hemoglobin.
Oxygen and carbon dioxide tensions in the blood were related to ventilation in two critical ways. Decreasing C ventilation would have the opposite effect. Because blood levels of oxygen and carbon dioxide could be measured, 1 physiologists now could assess the adequacy of ventila- tion. Decreased oxygen tensions and increased carbon dioxide tensions played a critical role in the chemical con- trol of ventilation. It was not understood, though, how carbon dioxide was carried by the blood until experiments performed by Bohr31 and Haldane.
By the s, a practical electrode became available for determin- 1 ing anaerobic blood pH,33 but pH was not thought to be useful clinically until the s. An enlarged view of the the high mortality rate in polio patients with respiratory lower part of B. Through the bottom of the narrow tube 1 in A, blood paralysis. Clinicians disagreed because high blood levels is introduced. By measuring pH, a fine jet and plays on the air bubble 2. Once equilibrium is reached Ibsen was proved correct, and clinicians became acutely between the air bubble and blood, the air bubble is drawn by the screw aware of the importance of determining both carbon diox- plunger 4 into the graduated capillary tube shown in B.
The volume of the air bubble is measured before and after treatment with KOH to ide levels and pH. The changes in such factors as base excess, duration of hypercapnia, and volume of the bubble reflect blood CO2 and O2 content. A model of renal buffering activity before Siggaard-Anderson pub- A designed for direct connection to a blood vessel.
The development of practical blood gas machines suitable for use in clinical medicine did not occur until electrodes levels. Stow built the first elec- the concomitant increase in cardiac output.
For 6 days he remained in a calomel electrode opening at its tip. Oxygen saturation of radial artery blood electrode.
This wrap trapped a film of distilled water over was always less than that of blood exposed to simultane- the electrode. The finger cot then acted as a semiperme- ously obtained alveolar gas, even during exercise.
These able membrane to separate the measuring electrode from were expected findings for gas transport based simply on the sample. Platinum electrodes were With this body of work, the chemists and physiolo- used as the measuring device, and polyethylene served as gists had provided the fundamental knowledge necessary the semipermeable membrane.
Oxygen able to commercially produce the first automated blood was the component of atmospheric gas understood to be gas analyzer, the ABL, capable of measuring PO2, PCO2, and essential for life.
Although these breathing tubes prolonged underwater activities, they did not enable Travel in the deep sea and flight have intrigued humankind divers to reach even moderate depths. Achieving these goals has followed a typical complete diving dress with tubes in the helmet for recirculat- pattern.
First, individual explorers tested the limits of human ing and purifying air in Fig. As mechanical devices were developed to extend Klingert described the first modern diving suit in These forces further pipes to an air reservoir that was large enough to have an intensified the need for safe and efficient underwater and associated platform.
The diver stood on the platform and high-altitude travel. Unfortunately, the development of vehi- inhaled from the air reservoir through an intake pipe on cles to carry humans aloft and under water proceeded faster the top of the reservoir and exhaled through a tube con- than the appreciation of the physiologic risks.
Calamitous nected to the bottom of the reservoir. Siebe made the first events ensued, with serious injury and death often a conse- commercially viable diving dress. The diver wore a metal quence. Only a clear understanding of the ventilatory prob- helmet riveted to a flexible waterproof jacket. In , Siebe modified this diving dress by extending the jacket to cover the whole body.
The suit was watertight at Exploration Under Water the wrists and ankles. Air was used in various forms by Alexander the Great at the siege pumped directly into the reservoir, and escape of air from of Tyre in bc, the Romans in numerous naval battles, the suit was adjusted by the diver.
This suit had a cop- own weight. When the bell was positioned at the bottom of per chamber containing potash for absorbing carbon dioxide fairly shallow bodies of water, workers were able to enter and and a cylinder of oxygen under pressure.
Unfortunately, these bells revised this diving suit in to include an oronasal mask had to be raised periodically to the surface to refresh the air. The inlet valve allowed Although the nature of the foul air was not understood, an inspiration from a metal chamber containing oxygen under important principle of underwater work, the absolute need pressure. Expiration through the exhaust valve was directed for adequate ventilation, was appreciated.
Construction of this appliance was in Fig. Old air was released through the top of the mine rescue work, where explosions and toxic gases previ- bell by a valve. In , Papin developed a technique for con- ously had prevented such efforts.
In , Smeaton diving suits, commercial divers began to dive deeper and replaced the bellows with a pump for supplying fresh air to longer. Unfortunately, complications developed for two the submerged bell. Decompression illness was recognized Techniques used to make diving bells practical also were first.
In , Lord Cochrane took out a patent in England applied to divers. In 77 ad, cally applied caisson for penetrating the quicksands of the Pliny described divers breathing through tubes while sub- Loire River Fig.
More sophisticated diving was sunk to a depth of 20 m. Small barrels of fresh air were lowered periodically to the bell, and the worker inside the bell released the air.
Workers could exit the bell for short periods. Used, with permission, from Hill. The high air pressure through an airlock. Once the in workers after they had left the pressurized caisson. As excavation reached the prescribed depth, the caisson was this new technology was applied increasingly in shaft and filled with cement, providing a firm foundation. During the tunnel work e. Bert was especially instrumental in pointing out the dangers of high pressure. The metal helmet devised by Siebe is still used today.
The complete diving suit produced by Siebe, Gorman, and Company bon dioxide levels reached a certain threshold. Carbon in the nineteenth century included the metal helmet, a diving dress sealed at the wrists and ankles, and weighted shoes. Used, with per- dioxide absorbents placed in the high-pressure chamber mission, from Hill.
Haldane understood that min- ute ventilation varied directly with alveolar carbon dioxide descended and pressure increased, pump ventilation at the levels. It appeared reasonable that the same minute ventila- surface necessarily also would have to increase to maintain tion needed to maintain an appropriate PA CO2 at sea level minute ventilation. Haldane realized that at 2 atmospheres would be needed to maintain a similar PA CO2 under water. Since , the modern submarine has been devel- oped primarily for military actions at sea.
Submarines are an intriguing physiologic experiment in simultaneously ventilating many subjects. Ventilation in submarines is complex because it involves not only oxygen and carbon dioxide levels but also heat, humidity, and body odors. Early work in submarines documented substantial increases in temperature, humidity, and carbon dioxide levels.
Exploration in the Air FIGURE The caisson is a complex device enabling workers to function in dry conditions under shallow bodies of water or in other potentially flooded circumstances. A tube composed of concentric In , the Montgolfier brothers astounded the world by rings opens at the bottom to a widened chamber, where workers can constructing a linen balloon about 18 m in diameter, filling be seen. At the top of the tube is a blowing chamber for maintaining it with hot air, and letting it rise about m into the air.
As with diving, however, the machines increase ventilatory demands. Unfortunately, early divers that carried them aloft brought human passengers past the did not appreciate the need to adjust ventilation to the limits of their physiologic endurance.
Glaisher and Coxwell diving suit. Furthermore, air pumps often leaked or were reached possibly 29, ft in , but suffered temporary maintained inadequately. Haldane demonstrated the rela- paralysis and loss of consciousness.
Surprisingly, how- protecting underwater workers from hypercapnia. Besides ever, he found that the fraction of inspired oxygen in high- his work with divers, Haldane also demonstrated that the altitude air was similar to that found in sea-level air.
In a remarkable series of observations during the Diving boats were fancifully described by Marsenius, s, Coindet described respiratory patterns of French in , and others. Only the boat designed by Debrell in people living at high altitude in Mexico City. In , they began their air of altitudes contains in a given volume less oxygen at historic attempt to set an altitude record supplied with a lower barometric pressure…[and therefore] a greater oxygen cylinders Fig.
Unfortunately, at 24, ft quantity of this air must be absorbed to compensate for they released too much ballast, and their balloon ascended the difference. When the balloon eventually decreased air elasticity, wind currents, exhalations from returned to earth, only Tissandier remained alive.
The idea that two men had died in support in blood vessels as other possible explanations the air was especially disquieting. In experiments on icit as the lethal threat and encouraged Berson to attempt animals exposed to low-pressure conditions in cham- further high-altitude balloon flights.
He originally devised bers Fig. Later, von Schrotter con- death. Supplemental oxygen, however, protected animals ceived the idea of a face mask to supply oxygen more easily from dying under simulated high-altitude conditions and also began to use liquid oxygen. With these devices, Fig.
More importantly, he recognized that death Berson reached 36, ft in When a mul- substantially changed the nature of flight. The mili- tiple of these two variables—that is, the partial pressure tary value of airplanes soon was appreciated and applied of oxygen—reached a critical threshold, death ensued. The Germans were especially inter- Croce-Spinelli, Sivel, and Tissandier were adventur- ested in increasing the altitude limits for their pilots. They ous French balloonists eager to reach the record height of applied the concepts advocated by von Schrotter and pro- m.
Used, with permission, from Bert. FIGURE A bird placed in a low-pressure bell jar can supplement the enclosed atmospheric air with oxygen inspired from the bag labeled O. Supplemental oxygen prolonged survival in these experiments. This suit provided oxygen under pressure and an flight across the Atlantic in Much work was done air circulator with a soda lime canister for carbon diox- on valves and oxygen gas regulators in the hope of fur- ide removal.
These suits proved quite successful, and soon ther improving altitude tolerance. A series of high-altitude pilots were exceeding heights of 50, ft. In , Lockheed produced 47, ft in This was clearly the limit for human the XC, which was the first successful airplane with endurance using this technology. The flight was achieved by Piccard, who enclosed an aeronaut German Air Ministry was particularly interested in devel- in a spherical metal chamber sealed with an ambient baro- oping oxygen regulators and valves and positive-pressure metric pressure equivalent to that of sea level.
The aero- face masks for facilitating high-altitude flying. Work throughout World War II defined limits for tech- This work recapitulated the important physiologic con- nological support of high-altitude flight.
Above altitude chambers, that oxygen availability is a function of this limit, oxygen-enriched air was essential. With flights both fractional inspired oxygen and barometric pressure. In tem—cabin, suit, or mask—was needed. Pressurization , Post devised a rubberized, hermetically sealed silk as an adjunct, however, reached its limit of usefulness at suit. In the same year, Ridge worked with Siebe, Gorman, approximately 80, ft. This plane reached a top speed of miles per hour at an altitude of , ft.
More importantly, the technology developed for this plane was a prelude to manned satellite programs. The United States Mercury and the Russian Vostok programs both relied on rockets to boost small, one-person capsules into space orbit. The Mercury capsule had a pure oxygen atmosphere at a reduced cabin pressure. In addition, the pilot wore a pressurized suit with an independent, closed oxygen supply.
In April , Gagarin was the first person to be launched into space. Shepard followed soon after, in May , and reached an altitude of miles.
More sophis- ticated space flight—in the Gemini, Apollo, and space sta- tion programs—was based on similar ventilation systems and principles. The Vivisection balloonist at the right can be seen inhaling from an oxygen tank. Unfortunately, the supplemental oxygen did not prevent tragic results from a too rapid ascent.
Used, with permission, from Armstrong HG. A completely sealed cabin was essential to pro- vivisection work. Galen operated on many living animals, tect passengers adequately from the rarefied atmosphere but his studies on the function of the heart were limited outside.
An altitude of 80, ft thus became a functional by the risk of pneumothorax. Opening the thoracic cavity definition of space because at this height complete control almost certainly resulted in death of the animal. Paracelsus, a contemporary of Vesa- lius, is reported to have used a similar technique around in attempting to resuscitate a human. Vesalius only avoided being burned at the stake by embarking on a pil- grimage to the Holy Land, but he died during the voyage.
Used, with permission, of ventilation during vivisection because he mentioned Armstrong HG. Principles and Practice of Aviation Medicine. Baltimore, artificial ventilation in his work later in England. Resuscitating the Apparantly Drowned Artificial respiration with a bellows and tracheal tube remained popular for vivisection work but was applied to humans only after a curious turn of events.
Attempts FIGURE An attempt at resuscitating an apparently drowned to resuscitate apparently dead people were first recorded person using the modified Dutch method.
One resuscitator is assisting in the mid-eighteenth century. The origins of this move- respiration by massaging the chest. Access through your institution. Add or change institution. Save Preferences.
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