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Flashcards in Altitude Deck (30):

Barometric pressure at sea level



Barometric pressure at 10,000 ft

523 mmHg


Barometric pressure @ 50,000 ft



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



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?



Acute effects of hypoxia at 12,000 ft (unacclimatized person)

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

1. Great increase in pulmonary ventilation
2. Increased nummbers of rbc
3. Increased diffusing capacity of the lungs
4. Increased vacularitu of the tissues
5. 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



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


Acclimatization to Low PO2 ( high altitudes)

> increased pulmonary ventilation
- decreased pH in the fluids
> increased RBC and Hgb conc
> increased diffusing capacity
- increased pulmonary capillary blood volume,
lung air volume, increase in pulmonary arterial
blood pressure
> increased CO
> increased tissue capillarity (angiogenesis)
> cellular acclimatization - increased # of mitochondria and cellular oxidatie enzyme systems


Work capacity is _________ (reduced/increased) in direct proportion to the decrease in maximum rate of oxygen uptake that the body can achieve



Acute mountain sickness and high altitude pulmonary edema

Two events that happen when some people ascend rapidly to high altitudes ( begins from a few hours up to about 2 days)

1. Acute cerebral edema
2. Acute pulmonary edema


Believed to result ffom local vasodilation of the cerebral blood vessels, caused by the hypoxia

Acute cerebral edema

Dilation of the arterioles increases blood flow into the capillaries, thus increasing capillary pressure, which causes leak into the cerebral tissues

Can lead to severe disorientation and other effects related to cerebral dysfunction


Cause is still unknown
Suggested answer: severe hypoxia causes the pulmonary arterioles to constrict potently; const is greater in some parts of the lungs; capillary pressure in these areas become especially high and local edema occurs

Acute pulmonary edema

Extension leads to spreading pulmonary edema & severe pulmonary dysfunction can be lethal

Allowing person to breathe oxygen usually reverses the process within hours


Chronic mountain sickness

When a person remains at high altitude for too long

1. The red cell mas and hct become exceptionally high
2. The pulmonary arterial pressure becomes elevated (even more than normal during acclimatization)
3. Right side of the heart becomes greatly enlarged
4. Peripheral arterial pressure begins to fall
5. Congestive heart failure ensues
6. Death, unless person is removed to a lower alt