High Altitude Physiology And Aviation - Dr. Miyake Flashcards
Mountain climbers and deep sea divers know the profound effects of __________ on human physiology.
Barometric pressure
Astronauts learn how physically equivalent forces of ________ and _________ affect the body.
Gravity and acceleration
As we ascend to higher and higher altitude, it has become more important to understand the effects of _______ and ________ on the human body.
Altitude
Low gas pressures
Barometric pressure (mmHg) at sea level 0
760 mmHg
As barometric pressure decreases, the atmospheric O2 partial pressure ___________ proportionately remaining at all times slightly <21% of totsl barometric pressure.
Decreases
Basic cause of all hypoxia problems in high-altitude physiology
Decrease in barometric pressure
CO2 continually excreted from pulmonary blood into alveoli
High altitudes
Water vaporizes into inspired air from respiratory surfaces
Altitudes
CO2 and water vapor _________ the alveolar oxygen.
Decrease
Water vapor pressure in alveoli remains at ______ mmHg at normal body temperature regardless of altitude.
47 mmHg
The difference between this 2 alveolar ventilation ________ much more in the acclimitized than in the unacclimatized person.
increases
In the acclimatized person, who increases his/her ventilation about fivefold, the PCO2 falls to about ___mmHg because of increased respiration.
7 mmHg
Up to an altitude of about 10,000 ft even when the air is breathed, the arterial oxygen saturation remains at least as high as ______%.
90%
Above 10,000 ft arterial O2 saturation falls rapidly until it is slightly less than ____% at 20,000 ft and much less at still higher altitudes.
70%
Saturation remains ___% until about 39,000 ft then it falls rapidly to about 50% at about 47,000 ft.
> 90%
Comparing 2 arterial blood O2 saturation curves breathing _________ in an unpressurized airplane can ascend to far higher altitudes.
Pure O2
The arterial saturation at 47,000 ft when breathing O2 is about ____% and equivalent to arterial O2 sat at 23,000 ft when breathing air.
50%
An unacclimatized person usually can remain conscious until the arterial O2 saturation falls to ___% for short exposure times.
50%
The ceiling for an aviator in unpressurized airplane when breathing air is about ________ and when breathing pure O2 is about _______ provided the O2 supplying equipment operates perfectly.
23,000 ft
47, 000 ft
Effects during the first few days at altitude (14,000 ft):
- Reduction in arterial PO2
- Stimulates peripheral chemoreceptors
- Cause increase in ventilation
- Has 2 effects
1st effect of 14,000 ft altitude:
- Increase in ventilation
2. Brings alveolar PO2 closer to ambient PO2
2nd effects at altitude (14,000 ft):
- Increase in ventilation
- Blows off CO2
- Effect is respiratory alkalosis
- Inhibits peripheral and central chemoreceptors
- Decrease ventilatory drive
To increase ventilatory drive:
- Increase in heart rate
- Increase in cardiac output
- Enhances O2 delivery
Effects during the next few days (>14,000 ft)
- Acclimitization occurs
- Causes ventilation to increase progressively by same amount as acute response
- PO2 improves, PCO2 decreases
Mechanisms to cause slow increase in ventilation
- pH of CSF decreases - counteracts respiratory alkalosis due to hyperventilation and offsets inhibition of central chemoreceptors
- Decreasing rate of acid secretion - done by kidneys due to respiratory alkalosis
2 results after kidney responds to respiratory alkalosis:
- Blood pH decreases toward normal
2. Spillage of HCO3 into the urine that leads to osmotic diuresis and production of alkaline urine
Mechanisms to cause slow increase in ventilation:
- Decrease pH of CSF
- Decrease plasma of pH
*These two removes part of inhibtion caused by alkaline pH -> allows hypoxia to drive ventilation to higher values.
Acute effects of hypoxia
- _______ person (breathing air)
- Beginning at altitude of ________ ft.
Unacclimatized person 12,000 ft * Drowsiness * Lassitude *Mental and muscle fatigue *Sometimes headache and euphoria *Occ nausea
Stage of twitchings or seizures above _________ in unacclimatized
18,000 ft
Stage of twitchings/seizures above _________ in acclimatized.
23,000 ft
- Coma
- Death
A person remaining at high altitudes for days, weeks or years becomes more and more ___________ to low PO2 so it causes fewer deletrious effects on the body,
acclimatized
Principal means by which acclimitization comes:
- Increase in pulmonary ventilation
- Increased numbers of RBC
- Increased diffusing capacity of the lungs
- Increased ability of tissue cells to use O2 despite low PO2
Principal stimulus for causing increas in RBC production
Hypoxia
Hematocrit rises from 40-45 to an average of about ______
60
Whole blood hemoglobin concentration from _________.
15 to 20 g/dL
Blood volume increase by _______
20-30%
Normal diffusing capacity for O2 thru pulmonary membrane
21 mL/mm Hg/min
Increase diffusing capacity:
Exercises and high altitude
Reasons why diffusing capacity increases:
- Increase pulmonary capillary blood volume
- Increase in lung air volume
- Increase in pulmonary arterial blood pressure
Expands capillaries and increase surface area thru which O2 diffuse into the blood
Increase pulmonary capillary blood volume
Expamds the surface area of alveolar - capillary interface
Increase in lung air volume
Forces blood into the greater numbers of alveolar capillaries
Increase in pulmonary arterial blood pressure
Cardiac output increases _____ immediately after person ascends to high altitude.
30%
___________ DECREASES back toward normal over period of weeks as blood hematocrit increases so amount of O2 transported to peripheral body tissues remains about normal.
Cardiac output
Growth of increase numbers of systemic circulatory capillaries in non pulmonary tissues called INCREASE TISSUE CAPILLARITY (_____________).
Angiogenesis
Active tissus exposed to _________, increased in capillarity is marked.
Chronic hypoxia
Natives in the Andes and Himalayas live at altitude above ___________.
13,000 ft
Acclimatization of natives begins in _________.
Infancy
- Chest size - increased
- Body size - decreased
- High ratio of ventilatory capacity to body mass
At high altitude, work capacity of all skeletal and cardiac muscles ________ in hypoxia.
Decreased
At high altitude, work capacity is ________ in direct proportion to decrease in maximum rate of O2 uptake.
Reduced
Unacclimatized work capacity
50%
Acclimatized for two months
68%
Native living at 13,200 ft but working at 17,000 ft.
87%
Acute mountain sickness
- Acute cerebral edema
2. Acute pulmonary edema
Acute cerebral edema
- Hypoxia
- Local vasodilation of cerebral blood vessels
- Increase blood flow into capillaries
- Increase capillary pressure
- Fluid leak into cerebral tissues
- Cerebral edema
Acute pulmonary edema:
- Hypoxia
- Pulmonary arterioles constrict
- Increase capillary pressure
- Local edema
Chronic mountain sickness
- Increase red cell mass
- Increase blood viscosity
- Decrease tissue blood flow
- Decrease O2 delivery
- Vasoconstricted pulmonary arterioles
- Divert blood flow from low O2 to high O2 alveoli
- Lung hypoxia
