Mountain sickness is the condition characterized by adverse effects of hypoxia at high altitude. It is commonly developed in persons going to high altitude for the first time. It occurs within a day in these persons, before they get acclimatized to the altitude.


In mountain sickness, the symptoms occur mostly in digestive system, cardiovascular system, respiratory system and nervous system. Symptoms of mountain sickness are:

1. Digestive System

Loss of appetite, nausea and vomiting occur because of expansion of gases in GI tract.

2. Cardiovascular System

Heart rate and force of contraction of heart increases.

3. Respiratory System

Pulmonary blood pressure increases due to increased blood flow. Blood flow increases because of vasodilatation induced by hypoxia. Increased pulmonary blood pressure results in pulmonary edema, which casus breathlessness.

4. Nervous System

Symptoms occuring in nervous system are headache, depression, disorientation, irritability, lack of sleep,

weakness and fatigue. These symptoms are developed because of cerebral edema. Sudden exposure to

hypoxia in high altitude causes vasodilatation in brain. Autoregulation mechanism of cerebral blood flow fails to cope with hypoxia. It leads to an increased capillary pressure and leakage of fluid from capillaries into the brain tissues.


Symptoms of mountain sickness disappear by breathing oxygen.


Acclimatization refers to the adaptations or the adjustments by the body in high altitude. While staying

at high altitudes for several days to several weeks, a person slowly gets adapted or adjusted to the low

oxygen tension, so that hypoxic effects are reduced. It enables the person to ascent further.


Various changes that take place during acclimatization help the body to cope with adverse effects of hypoxia at high altitude. Following changes occur in the body during acclimatization:

1. Changes in Blood

During acclimatization, RBC count increases and packed cell volume rises from normal value of 45% to

about 59%. Hemoglobin content in the blood rises from 15 g% to 20 g%. So, the oxygen carrying capacity of the blood is increased. Thus, more oxygen can be carried to tissues, in spite of hypoxia. Increase in packed cell volume and hemoglobin content is due to erythropoietin actions. Increase in RBC count, packed cell volume and hemoglobin content is due to erythropoietin, that is released from juxtaglomerular apparatus of kidney.

2. Changes in Cardiovascular System

Overall activity of cardiovascular system is increased in high altitude. There is an increase in rate and force of contraction of the heart and cardiac output. Vascularity in the body is increased due to vasodilatation induced by hypoxia. So, blood flow to vital organs such by hypoxia. So, blood flow to vital organs such as heart, brain, muscles, etc. increases.

3. Changes in Respiratory System

i. Pulmonary ventilation

Pulmonary ventilation increases up to 65%. This is the immediate compensation for hypoxia in high altitude and this alone helps the person to ascend several thousand feet. Increase in pulmonary ventilation is due to the stimulation of chemoreceptors.

ii. Pulmonary hypertension

Increased cardiac output increases the pulmonary blood flow that leads to pulmonary hypertension. It is very common even in persons acclimatized to high altitude. In some of these persons, pulmonary hypertension is associated with right ventricular hypertrophy.

iii. Diffusing capacity of gases

Due to increased pulmonary blood flow and increased ventilation, diffusing capacity of gases increases in

alveoli. It enables more diffusion of oxygen in blood.

4. Changes in Tissues

Both in human beings and animals residing at high altitudes permanently, the cellular oxidative enzymes

involved in metabolic reactions are more than the inhabitants at sea level. Even when a sea level inhabitant stays at high altitude for certain period, the amount of oxidative enzymes is not increased. So, the elevation in the amount of oxidative enzymes occurs only in fully acclimatized persons. An increase in the number of mitochondria is observed in these persons.

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