1. Physiology ofPhysiology of
High AltitudeHigh Altitude
by :by : Jagjit KhoslaJagjit Khosla

2. High Altitude
• A height above 10,000 feet (3000 m) above the sea
level is defined as High Altitude
• According to Dalton’s law, total pressure of air is equal
to sum of partial pressures of gases it contains.
P = pO2 + pCO2 + pN2 + pH2O
• pH2O and pCO2 doesn’t depend upon altitude.
• pO2 and pN2 decrease with increase in height.
• At High Altitude, low partial pressure of O2 leads to
Hypoxia.

3. Effects of High Altitude on
O2-Hb Saturation
50%
60%
70%
80%
90%
100%
Sea
level
5,000
feet
10,000
feet
15,000
feet
20,000
feet
25,000
feet
30,000
feet
Oxygen -Hb Saturation Curve
• Above 10,000 feet, the
arterial oxygen saturation
falls rapidly.
• It is due to increased
2,3- DPG concentration
in RBCs
• It is slightly less than 70%
at 20,000 feet and much
less at higher altitudes.

4. Effects of High Altitude on
Human body
Level of
Altitude (ft)
Common effects
5,000 No effects
10,000 No hypoxia upto pO2 60 mmHg
Rapid ascent upto 10,000 ft is Safe zone
of ascent.
15,000 Moderate hypoxia with CVS and
respiratory symptoms
18,000 Severe hypoxia with involvement of CNS
20,000 Hypoxia aggravates. Unconsciousness
when Hb saturation falls below 60%
Critical Survival Altitude
30,000 Severe hypoxia even with oxygen
therapy

5. Effects of High Altitude
• Effect of Hypoxia
• Effect of expansion of gases
• Effect of fall in atmospheric
temperature
• Effect of light rays

6. Effect of Hypoxia
• On Blood -
> Increased RBC count
> Due to increased secretion of erythropoietin from JGA
of kidney
• On CVS -
> Increased Heart rate, Force of contraction of heart,
Cardiac output, Blood pressure
> Due to Reflex stimulation of Cardiac and vasomotor
centers
• On Respiration -
> Increased pulmonary ventilation
> Due to chemoreceptor reflex following increased pCO2

7. Effect of Hypoxia
• On Digestive system -
> Loss of appetite, nausea, vomiting
• On Kidney -
> Alkaline urine due to increased erythropoietin secretion
• On CNS -
> Depression, Apathy with general loss of self control
> Talkative, quarrelsome, ill-tempered, rude
> Disorientation, Loss of power of judgement
> Memory impaired, fatigue, lack of coordination
> In acute/ severe hypoxia, sudden loss of
consciousness

8. Effect of Expansion of gases
According to Boyle’s law, as the atmospheric
pressure decreases with altitude, volume of gases
increases proportionally.
• In GIT -
> Painful distention of stomach and intestine
• In Lungs-
> Expansion of gases may destroy alveoli
• Rapid ascent may cause-
> Decompression sickness

9. Effect of Fall in
Atmospheric Temperature
The atmospheric temperature falls by 2o
C for every
1000 ft increase in altitude above sea level.
• Effects -
> Widespread cutaneous vasoconstriction.
> Prolonged and severe vasoconstriction may lead to
tissue damage known as Frost-bite.

10. Effect of Light rays
Ultraviolet (UV) rays at high altitude also cause
many hazardous effects such as skin irritation.

11. Acute Mountain Sickness
It refers to the symptom
complex which occurs in an
individual residing at sea
level, when he ascends to
high altitude over a period
of 1-2 days for the first
time. The symptoms
develop 8 to 24 hours after
arrival at high altitude and
last for 4 to 8 days.

12. Acute Mountain Sickness
• Symptoms -
> Digestive system - Loss of appetite, nausea, vomiting
> Respiratory system - Breathlessness,
High Altitude Pulmonary Edema (HAPE)
> Nervous System - Irritability, Insomnia, headache,
depression, High Altitude Cerebral Edema (HACE)
• Treatment -
> Decreasing Cerebral edema - administration of large
doses of Glucocorticoids
>Decreasing alkalosis -administration of Acetazolamide.
Acetazolamide decreases H+
excretion through kidneys
by inhibiting the enzyme carbonic anhydrase.

13. Chronic Mountain Sickness
• Also called Monge’s disease
• It occurs in some long-term residents of high altitude
• Effects -
> Extreme polycythemia
> Pulmonary arterial pressure becomes elevated
> Right side of heart becomes greatly enlarged
> Peripheral arterial pressure begins to fall
> Congestive heart failure
> Death follows if left untreated
• These individuals must be removed to a lower altitude to
prevent rapid development of fatal pulmonary edema.

14. High Altitude Pulmonary Edema
• Occurs due to -
> Rapid Ascent
> Doing heavy physical work during first 3-4 days after
rapid ascent to high altitude.
• Mechanism -
> Increased sympathetic activity
> produces vasoconstriction which leads to increase in
Pulmonary capillary hydrostatic pressure.
> drives the fluid out of the pulmonary capillaries
producing pulmonary edema.
• Treatment -
> O2 therapy
> Administration of Ca2+
channels blocker e.g. Nifedipine

15. High Altitude Cerebral Edema
• Mechanism -
> Low pO2 cause arteriolar dilation which is normally
compensated by cerebral autoregulation.
> Once the limit of cerebral circulation autoregulatory
mechanism is reached, there occurs an increase in
capillary pressure.
> It favours increased transudation of fluid into brain
tissue.
• Treatment -
> Administeration of large doses of Glucocorticoids

16. Acclimatization
• Definition -
It refers to changes in body tissues in
response to long-term exposure to high
altitude hypoxia, such as when a person
living at sea level goes and stays at high
altitude for a long time.
• Changes in the body -
> Blood
- Increased haematocrit to 60%
- Increased Hb conc. to about 20g%
- due to increased erythropoietin
secretion

17. Acclimatization
> Respiration
- Increased Pulmonary ventilation and blood flow
- Increased diffusing capacity of lungs
- Due to stimulation of chemoreceptors
> CVS
- Increased Heart rate, cardiac output and BP
- Increased blood flow to vital organs like heart,
brain, muscles, etc.
> Tissues
- Increased quantities of oxidative enzymes
involved in metabolism present in cells
- Increased number of mitochondria in cells
- Increased myoglobin content

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