Ebook Guyton and hall textbook of medical physiology (12/E): Part 2
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Ebook Guyton and hall textbook of medical physiology (12/E): Part 2
VIII1Aviation, Space, and Deep-Sea Diving Physiology43Aviation, High Altitude, and space Physiology44Physiology of Deep-Sea Diving and Other Hyperbari Ebook Guyton and hall textbook of medical physiology (12/E): Part 2ic ConditionsCHAPTER 43UNIT VAviation, High Altitude, and Space Physiology mAs humans have ascended to higher and higher altitudes in aviation, mountain climb ing, and space vehicles, il has become progressively more important to understand the effects of altitudeand low gas pressures on the human b Ebook Guyton and hall textbook of medical physiology (12/E): Part 2ody. This chapter deals with these problems, as well as accelerator)- forces, weightlessness, and other challenges to body homeostasis that occur at hEbook Guyton and hall textbook of medical physiology (12/E): Part 2
igh altitude and in space flightEffects of Low Oxygen Pressure on the BodyBarometric Pressures at Different Altitudes. Table 43-1 gives the approximatVIII1Aviation, Space, and Deep-Sea Diving Physiology43Aviation, High Altitude, and space Physiology44Physiology of Deep-Sea Diving and Other Hyperbari Ebook Guyton and hall textbook of medical physiology (12/E): Part 2m 1 Ig; and at 50,000 feet, 87 mm 11g. This decrease in barometric pressure is the basic cause <11 all the hypoxia problems in high-altitude physiology because, as Lhe barometric pressure decreases, the atmospheric oxygen partial pressure (Po,) decreases proportionately, remaining at all times sligh Ebook Guyton and hall textbook of medical physiology (12/E): Part 2tly less than 21 percent of the total Ixiromelric pressure; al sea level p<>._ is about 159mm Hg, but at 50,000 feet Po2 is only 18 mm 11g.Alveolar PoEbook Guyton and hall textbook of medical physiology (12/E): Part 2
2 at Different ElevationsCarbon Dioxide and Water Vapor Decrease the Alveolar Oxygen. Even at high altitudes, carbon diox ide is continually excreted VIII1Aviation, Space, and Deep-Sea Diving Physiology43Aviation, High Altitude, and space Physiology44Physiology of Deep-Sea Diving and Other Hyperbari Ebook Guyton and hall textbook of medical physiology (12/E): Part 2n in the alveoli, thus reducing the oxygen con ccntration. Water vapor pressure in the alveoli remains al 47 mm Hg as long as the body temperature Is normal, regardless of altitude.In the case of carbon dioxide, during exposure to very high altitudes, the alveolar Pco, falls from the sea level value Ebook Guyton and hall textbook of medical physiology (12/E): Part 2 of 40mm Hg to lower values. In the acclimatized person, who increases his or her ventilation aboutfivefold, the Pco falls to about 7 mm Hg because ofEbook Guyton and hall textbook of medical physiology (12/E): Part 2
increased respiration.Now let us see how the pressures of these two gases affect the alveolar oxygen. For instance, assume that the barometric pressuVIII1Aviation, Space, and Deep-Sea Diving Physiology43Aviation, High Altitude, and space Physiology44Physiology of Deep-Sea Diving and Other Hyperbari Ebook Guyton and hall textbook of medical physiology (12/E): Part 2even mm Hg of this must be waler vapor, leaving only 206mm 11g for all the other gases. In the acclima tized person, 7 mm of the 206 mm 11g must be carbon dioxide, leaving only 199mm Hg. If there were no use of oxygen by the body, one fifth of this 199 mm 1 Ig would be oxygen and four fifths would b Ebook Guyton and hall textbook of medical physiology (12/E): Part 2e nitrogen; that is, the Po. in the alveoli would be 40 mm 1 Ig. 1 lowever, some of this remaining alveolar oxygen is continually being absorbed intoEbook Guyton and hall textbook of medical physiology (12/E): Part 2
the blood, leaving about 35 mm i Ig oxygen pressure in the alveoli. At the summit of Mount Everest, only the best of acclimatized people can barely suVIII1Aviation, Space, and Deep-Sea Diving Physiology43Aviation, High Altitude, and space Physiology44Physiology of Deep-Sea Diving and Other Hyperbari Ebook Guyton and hall textbook of medical physiology (12/E): Part 2o? at Different Altitudes. The filth column of Table 43 1 shows the approximate Po,s in the alveoli at different altitudes when one is breathing air tor both the unacclimatized and the acclimatized person. At sea level, the alveolar Po; is 104 mm 1 Ig; at 20,000 feet altitude, it falls to about 40mm Ebook Guyton and hall textbook of medical physiology (12/E): Part 2 Hg in the unacclimatized person but only to 53 mm 1 Ig in the acclimatized person. The difference between these two is that alveolar ventilation incrEbook Guyton and hall textbook of medical physiology (12/E): Part 2
eases much more in the acclimatized person than in the unacclimatized person, as we discuss later.Saturationof Hemoglobin with Oxygenat Different AltiVIII1Aviation, Space, and Deep-Sea Diving Physiology43Aviation, High Altitude, and space Physiology44Physiology of Deep-Sea Diving and Other Hyperbari Ebook Guyton and hall textbook of medical physiology (12/E): Part 2altitude of about 10,000 feet, even when air is breathed, the arterial oxygen saturation remains at least as high as 90 percent. Above 10,000 feet, the arterial oxygen saturation falls rapidly, as shown by the blue curve of the figure, until it is slightly less than 70 percent at 20,000 feet and muc Ebook Guyton and hall textbook of medical physiology (12/E): Part 2h less at still higher altitudes.527Unit VIII Aviation, Space, and Deep-Sea Diving PhysiologyTable 43-1 Effects of Acute Exposure to Low Atmospheric PEbook Guyton and hall textbook of medical physiology (12/E): Part 2
ressures on Alveolar Gas Concentrations and Arterial Oxygen Saturation*Breathing AirBreathing Pure OxygenAltitude (ft/meters) 0Barometric Pressure (mmVIII1Aviation, Space, and Deep-Sea Diving Physiology43Aviation, High Altitude, and space Physiology44Physiology of Deep-Sea Diving and Other Hyperbari Ebook Guyton and hall textbook of medical physiology (12/E): Part 2 40POj in Alveoli (mm Hg) 673Arterial Oxygen Saturation (%) 10010.000/304852311036(23)67(77)90(92)4043610020.000/60%3497324 (10)40(53)73(85)40262100'30.000/91442264724(7)18(30)24(38)401399940.000/12,1921412936588450.000/15,2408718241615’Numbers KI parentheses ate acclimatised values.Figure 43-1 Effe Ebook Guyton and hall textbook of medical physiology (12/E): Part 2ct of high altitixie on arterial oxygen saturation when breathing air and when breathing pure oxygen.Effect of Breathing Pure Oxygen on Alveolar Po?atEbook Guyton and hall textbook of medical physiology (12/E): Part 2
Different AltitudesWhen a person breathes pure oxygen instead of air. most of the space in the alveoli formerly occupied by nitrogen becomes occupiedVIII1Aviation, Space, and Deep-Sea Diving Physiology43Aviation, High Altitude, and space Physiology44Physiology of Deep-Sea Diving and Other Hyperbari Ebook Guyton and hall textbook of medical physiology (12/E): Part 2he rod curve of Figure 43 1 shows arterial blood hemoglobin oxygen saturation at different altitudes when one is breathing pure oxygen. Note that the saturation remains above 90 percent until the aviator ascends to about 39,000 feet; then it falls rapidly to about 50 percent at about 47.000 feet.The Ebook Guyton and hall textbook of medical physiology (12/E): Part 2 "Ceiling" When Breathing Air and When Breathing Oxygen in an Unpressurized AirplaneComparing the two arterial blood oxygen saturation curves in FigurEbook Guyton and hall textbook of medical physiology (12/E): Part 2
e 43-1. one notes that an aviator breathing pure oxygen in an unpressurized airplane can ascend to far higher altitudes than one breathing air. For inVIII1Aviation, Space, and Deep-Sea Diving Physiology43Aviation, High Altitude, and space Physiology44Physiology of Deep-Sea Diving and Other Hyperbari Ebook Guyton and hall textbook of medical physiology (12/E): Part 2t 23,(XX) feel when one is breathing air. In addition, because an unacclimatized person usually can remain conscious until the arterial oxygen saturation falls to 50 percent, for short exposure limes the ceiling lor an aviator in an unpressurized airplane when breathing air is about 23.ÍXX) feel and Ebook Guyton and hall textbook of medical physiology (12/E): Part 2 when breathing pure oxygen is about 47,000 feet, provided the oxygen supplying equip menl operates perfectly.VIII1Aviation, Space, and Deep-Sea Diving Physiology43Aviation, High Altitude, and space Physiology44Physiology of Deep-Sea Diving and Other HyperbariVIII1Aviation, Space, and Deep-Sea Diving Physiology43Aviation, High Altitude, and space Physiology44Physiology of Deep-Sea Diving and Other HyperbariGọi ngay
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