Effects Of Low Oxygen Pressure On The Body
Barometric Pressures at Different Altitudes
•Table 44-1 lists the approximate
barometric and oxygen pressures at different
altitudes, showing that at sea level, the
barometric pressure is 760 mm Hg; at 10,000
feet, it is only 523 mm Hg; and at 50,000 feet,
it is 87 mm Hg.
•This decrease in barometric pressure is
the basic cause of all the hypoxia problems in
high-altitude physiology because, as the
barometric pressure decreases, the
atmospheric oxygen partial pressure (PO2)
decreases proportionately, remaining at all
times slightly less than 21 percent of the total
barometric pressure; at sea level, PO2 is about
159 mm Hg, but at 50,000 feet, PO2 is only
18 mm Hg.
Alveolar Po2 At Different Elevations
Carbon Dioxide and Water Vapor Decrease
the Alveolar Oxygen.
•These two gases dilute the O2 in the alveoli,
thus reducing the O2 concentration. Water
vapor pressure in the alveoli remains at 47
mm Hg as long as the body temperature is
normal, regardless of altitude.
•In the case of CO2, during exposure to very
high altitudes, the alveolar partial pressure of
CO2 (PCO2) falls from the sea-level value of
40 mm Hg to lower values. In the
acclimatized person, who increases ventilation
about fivefold, the PCO2 falls to about 7 mm
Hg because of increased respiration.
Alveolar Po2 at Different Altitudes
•The fifth column of Table 44-1 shows the
approximate PO2 values in the alveoli at
different altitudes when one is breathing air
for both the unacclimatized and the
acclimatized person.
•At sea level, the alveolar PO2 is 104 mm Hg.
At 20,000 feet altitude, it falls to about 40 mm
Hg in the unacclimatized person but only to
53 mm Hg in the acclimatized person.
•The reason for the difference between these
two is that alveolar ventilation increases much
more in the acclimatized person than in the
unacclimatized person, as we discuss later.
Saturation of Hemoglobin with Oxygen at
Different Altitudes
•Figure 44-1 shows arterial blood O2 saturation
at different altitudes while a person is
breathing air and while breathing O2.
•Up to an altitude of about 10,000 feet, even
when air is breathed, the arterial O2 saturation
remains at least as high as 90 percent. Above
10,000 feet, the arterial O2 saturation falls
rapidly.
CHAPTER 44: Aviation, High Altitude, and Space Physiology
Dr. Paloma | January 28, 2019
Nasinopa
OUTLINE:
I. Effects Of Low Oxygen Pressure On The Body
A. Alveolar Po2 At Different Elevations
B. Effect Of Breathing Pure Oxygen On Alveolar Po2
At Different Altitudes
C. Acute Effects Of Hypoxia
D. Acclimatization To Low Po2
E. Hypoxia Inducible Factors
F. Natural Acclimatization Of Native Human Beings
Living At High Altitudes
G. Reduced Work Capacity At High Altitudes And
Positive Effect Of Acclimatization
H. Acute Mountain Sickness And High Altitude
Pulmonary Edema
I. Chronic Mountain Sickness
II. Effects Of Acceleratory Forces On The Body In
Aviation And Space Physiology
A. Centrifugal Acceleratory Forces
B. Effects Of Centrifugal Acceleratory Force On The
Body (Positive G)
C. Effects Of Linear Acceleratory Forces On The Body
III. “Artificial Climate” In The Sealed Spacecraft
IV. Weightlessness In Space
V. References
