1.1 Barometric Pressures at Different Altitude

• What is the barometric pressure at sea level?

  760 mm Hg
• What is the barometric pressure at 10,000 feet?

  523 mm Hg
• What is the barometric pressure at 50,000 feet?

  87 mm Hg
• Why does decreased barometric pressure cause hypoxia problems?

  It decreases atmospheric oxygen partial pressure
• What is the atmospheric oxygen partial pressure (PO2) at sea level?

  159 mm Hg
• What is the atmospheric oxygen partial pressure (PO2) at 50,000 feet?

  18 mm Hg
• What gases dilute O2 in the alveoli at high altitudes?

  Carbon dioxide and water vapor
• What is the water vapor pressure in the alveoli at normal body temperature?

  47 mm Hg
• How does the alveolar partial pressure of CO2 (PCO2) change at high altitudes?

  It falls from 40 mm Hg to lower values
• What happens to PCO2 in an acclimatized person at high altitudes?

  It falls to about 7 mm Hg
• What is the barometric pressure at the top of Mount Everest?

  253 mm Hg
• How much of the barometric pressure at Mount Everest is water vapor?

  47 mm Hg
• What is the remaining pressure for gases other than water vapor at Mount Everest?

  206 mm Hg
• How much CO2 is present in the remaining gases at Mount Everest?

  7 mm Hg
• What is the alveolar O2 pressure if no O2 is used by the body?

  40 mm Hg
• What is the actual alveolar O2 pressure after absorption into the blood?

  35 mm Hg
• What is the alveolar PO2 at sea level?

  104 mm Hg
• What is the alveolar PO2 at 20,000 feet for an unacclimatized person?

  40 mm Hg
• What is the alveolar PO2 at 20,000 feet for an acclimatized person?

  53 mm Hg
• What factors contribute to the difference in alveolar PO2 between acclimatized and unacclimatized persons at high altitudes?

  • Increased alveolar ventilation in acclimatized persons
  • Greater adaptation to lower oxygen levels
  • Enhanced respiratory response to altitude
• What is the alveolar PO2 at sea level?

  104 mm Hg
• How does the alveolar PO2 change at 20,000 feet for an unacclimatized person?

  It falls to about 40 mm Hg
• What is the alveolar PO2 at 20,000 feet for an acclimatized person?

  It falls to 53 mm Hg
• Why does the alveolar PO2 differ between acclimatized and unacclimatized persons at high altitudes?

  Alveolar ventilation increases more in acclimatized persons
• What does Figure 44-1 illustrate regarding arterial blood O2 saturation at different altitudes?

  It shows saturation while breathing air and O2
• What is the arterial O2 saturation at altitudes up to 10,000 feet?

  At least 90 percent
• How does arterial O2 saturation change above 10,000 feet?

  It falls rapidly
• What is the arterial O2 saturation at 20,000 feet?

  Slightly less than 70 percent
• What happens to arterial O2 saturation at altitudes higher than 20,000 feet?

  It decreases much further