1.2 Effects of Breathing Pure Oxygen on Alveolar PO2

• What happens to the alveoli when breathing pure O2?

  Most nitrogen space is occupied by O2
• What is the alveolar PO2 at 30,000 feet when breathing pure O2?

  139 mm Hg
• What is the alveolar PO2 when breathing air at 30,000 feet?

  18 mm Hg
• What does the red curve in Figure 44-1 represent?

  Arterial blood hemoglobin O2 saturation
• How does arterial blood O2 saturation change at high altitudes when breathing pure O2?

  It remains above 90% until 39,000 feet
• What happens to O2 saturation at about 47,000 feet?

  It falls rapidly to about 50 percent
• What is the ceiling for an aviator breathing air in an unpressurized airplane?

  About 23,000 feet
• What is the ceiling for an aviator breathing pure O2 in an unpressurized airplane?

  About 47,000 feet
• What is the effect of hypoxia at about 12,000 feet?

  Drowsiness, lassitude, and fatigue occur
• What are some symptoms of hypoxia above 18,000 feet?

  Twitchings or seizures may occur
• What is the outcome of hypoxia above 23,000 feet?

  Coma followed by death
• How does hypoxia affect mental proficiency at 15,000 feet?

  Mental proficiency falls to about 50%
• What is the mental proficiency after 18 hours at 15,000 feet?

  About 20% of normal
• What is the relationship between altitude and mental proficiency in hypoxia?

  Mental proficiency decreases as altitude increases
• What are the acute effects of hypoxia in unacclimatized individuals?

  • Drowsiness
  • Lassitude
  • Mental and muscle fatigue
  • Headache
  • Nausea
  • Euphoria
  • Twitchings or seizures above 18,000 feet
  • Coma and death above 23,000 feet
• What are the saturation levels of arterial blood O2 at different altitudes when breathing pure O2?

  • Above 90% until 39,000 feet
  • Falls to about 50% at 47,000 feet
• What is the significance of the "ceiling" for aviators?

  • Breathing air: ceiling is about 23,000 feet
  • Breathing pure O2: ceiling is about 47,000 feet
• What is acclimatization to low PO2?

  Adaptation to low oxygen at high altitudes
• What happens to the body after acclimatization to low PO2?

  Fewer deleterious effects and increased work capacity
• What are the principal means of acclimatization to low PO2?

  Increased ventilation, red blood cells, and more
• What are the five principal means of acclimatization to low PO2?

  1. Increased pulmonary ventilation
  2. Increased numbers of red blood cells
  3. Increased diffusing capacity of the lungs
  4. Increased vascularity of peripheral tissues
  5. Increased ability of tissue cells to use O2
• How does immediate exposure to low PO2 affect pulmonary ventilation?

  It stimulates arterial chemoreceptors to increase ventilation
• By how much can alveolar ventilation increase due to low PO2?

  Up to 1.65 times normal
• What happens to ventilation after several days at high altitude?

  Ventilation can increase to about five times normal
• What effect does increased pulmonary ventilation have on CO2 levels?

  It blows off CO2, reducing PCO2 and increasing pH
• What causes the fading inhibition of the respiratory center during acclimatization?

  Reduction of bicarbonate ion concentration in cerebrospinal fluid
• How do kidneys compensate for respiratory alkalosis during acclimatization?

  By reducing hydrogen ion secretion and increasing bicarbonate excretion
• What is the normal hematocrit value before acclimatization?

  40 to 45
• What can the hematocrit rise to during acclimatization?

  About 60
• How much can blood volume increase during acclimatization?

  By 20 to 30 percent
• What is the increase in total body hemoglobin during acclimatization?

  50 percent or more
• What is the normal diffusing capacity for O2 through the pulmonary membrane?

  About 21 ml/mm Hg/min
• How much can diffusing capacity increase during exercise?

  As much as threefold
• What contributes to the increase in diffusing capacity at high altitude?

  Increased pulmonary capillary blood volume and surface area
• What happens to cardiac output immediately after ascending to high altitude?

  It can increase as much as 30 percent
• What happens to cardiac output over weeks after acclimatization?

  It decreases back toward normal levels
• What is increased tissue capillarity also known as?

  Angiogenesis
• In which tissues is capillary density especially marked during acclimatization?

  In active tissues exposed to chronic hypoxia
• How do cell mitochondria and oxidative enzyme systems differ in high altitude animals?

  They are more plentiful than in sea-level inhabitants
• What is presumed about tissue cells of high altitude-acclimatized humans?

  They can use O2 more effectively than sea-level counterparts