Altitude Flashcards
Barometric pressure at 10,000 ft
523 mmHg
Barometric pressure at sea level
760mmHg
Barometric pressure @ 50,000 ft
87mmHg
The basic cause of all hypoxia problems in high altitude physiology
Decrease in barometric pressure
As the barometric pressure decreases, what happens to the atmospheric oxygen partial pressure?
The atm oxygen partial pressure decreases proportionately, remaining at all times slightly less than 21% of the total barometric pressure
Two gases that dilute the oxygen in the alveoli
Carbon dioxide and water vapor
Water vapor pressure in the alveoli at room temp
47mmHg
What happens to alveolar PCO2 during exposure to very high altitudes?
- The alveolar PCO2 falls from sea level value of 40mmHg to lower levels
- the acclimatized person increases his ventilation to five fold - 7mmHg because of increased respiration
As the altitude goes higher the alveolar ventilation increases much more in the _________ person. (acclimatized/unaclimatized)
Acclimatized person
At about 10,000 ft, even wen air is breathed, the arterial oxygen saturation remains ______
At least as high as 90%
Above 10,000 ft, art oxygen saturation falls rapidly
*when breathing air
When breathing pure oxygen, the aviators alvelolar oxygen sat remain 90% at about how many feet?
39,000 ft
Then it fall rapidly to abt 50% at 47,000 ft
An unacclimatized person usu can remain conscious until the arterial oxygen saturation falls to what percent?
50%
Acute effects of hypoxia at 12,000 ft (unacclimatized person)
Drowsiness Lassitude Mental and muscle fatigue Sometimes headache, euphoria Occasionally nausea
Acute effects of hypoxia at above18,000 ft (unacclimatized person)
Twitchings or seizures
Acute effects of hypoxia above 23,000 ft (unacclimatized person)
Coma and death
One of the most impt effects of hypoxia
Decreased mental proficiency
- decreased judgement, memory, & performance of discrete motor movements
The principal means by which acclimatization comes about
- Great increase in pulmonary ventilation
- Increased nummbers of rbc
- Increased diffusing capacity of the lungs
- Increased vacularitu of the tissues
- Increased ability of the tissue cells to use oxygen despite low PO2
Immediate exposure to low PO2 stimulates the arterial chemoreceptors leads to…?
Increased alveolar ventilation
to a maximun of abt 1.65 times normal
What effect would the immediate increase in pulmonary ventilation on rising altitude have on PCO2 and body fluid pH?
Large quantities of CO2 are blown off,
reducing the PCO2, &
increasing the pH of the body fluids
*these changes inhibit the brain stem respiratory center and thereby oppose the effect of low PO2 to stimulate respiration by way of the peripheral arterial chemoreceptors in the carotid and aortic bodies. Ensuing 2-5 days this inhibition fades away, and ventilation increases to 5x normal
The kidneys respond to decreased PCO2 by what mechanism?
Reducing hyrogen ion secretion and increasing bicarbonate excretion
The principal stimulus for causing an increase in rbc production
Hypoxia
The normal diffusing capacity for oxygen thru the pulmonary membrane
21 mL/mmHg/min
What factors increase the diffusing capacity for oxygen (after acclimatization)
Exercise (3x)
At high altitudes
Increased pulmonary capillary blood volume
Increase in lung air volume
Increase in pulmonary arterial blood pressure
Peripheral circulatory system changes during acclimatization
- Increased CO to as much as 30% but decreases back to normal in weeks as the blood hct increases
- growth of increased numbers of systemic circulatory capillaries in the nonpulmonary tissues/ increased tissue capillary (angiogenesis) - also in active tissues exposed to chronic hypoxia
