Climbing a mountain

Climbing a mountain is a strenous activity which increases the metabolic demand of the muscle cells. This causes the ventilation rate and breathing frequency to increase as a response to supply he muscles with oxygen.

High altitudes

At high altitudes the atmospheric pressure is lower which lowers the partial pressure on oxygen. This in turn decreases the density of oxygen in the air. Thus the air that is delivered to the lungs and into the alveolus has a lower density of oxygen which affects the uptake of oxygen negatively. This can cause environmental hypoxia.

In the next slides I will explain the changes in the respiratory and circulatory system for a person at a high altitude. The changes that occur can be a step towards acclimatization but some can also be pathological.

When less oxygen is delivered through the arteries this causes two things to happen.

First, the amount of oxygen delivered to the tissues decreases which cause capillary density and concentration of myoglobin to increase.

This act as a negative feedback loop on the oxygen delivery to the tissues as it works to increase the efficiency of the oxygen delivery.

The low amount of oxygen delivered to the tissues also signals to the kidneys to synthesize more erythropoietin – a glycoprotein hormone that controls the synthesis of red blood cells by promoting the survival of red blood cell precursors in the bone marrow.

The increase in erythropoietin also act as a negative feedback as it acts to the delivery of oxygen to the tissues more efficient.

Lastly the low O2 delivered to tissues act to raise the levels of 2,3-Disphosphoglycerate (2,3-DPG).

The 2,3-DPG is present in human erythrocytes (red blood cells). It has a chemical conformation that gives it greater affinity for deoxygenated than oxygenated hemoglobin. When it binds to the deoxygenated hemoglobin it interacts with the hemoglobins beta subunits and decreases their affinity for oxygen.

This makes the hemoglobin release remaining oxygen and thus increasing the efficiency of the oxygen delivery.

The second effect of low amounts of oxygen in the arteries is that it increases the peripheral chemoreceptor firing rate which in turn signals to the medullary central pattern generators in that area to increase the rate of ventilation – you start to hyperventilate.

This aims to increase the amount of air flowing in and out of the lungs and thus act as a negative feedback loop, but if the air is very low in oxygen that alone is not enough.

If the hyperventilation continues without generating enough oxygen it can result in a condition called “respiratory alkalosis”.

In this condition the amount of CO2 is too low in the blood (due to the intense breathing) and the blood gets too alkaline, >7.45. This condition raises the hemoglobins affinity for oxygen, which counteracts the effects of the 2,3-DPG.

Also, even before the actual alkalosis, the CO2 in the blood is the primary trigger for the breathing reflex. Thus low CO2 in the blood may cause difficulties in breathing.

Symptoms of hypoxia:• Fatigue• Lack of cognition• Lethargic• Headaches• State of euphoria• Shortness of breath• Loss of Consciousness• Pins and needles• High pulse rate• Deterioration of vision• Blue lips and fingernails• Moodiness• Drowsiness

Remedies for hypoxia

The primary remedy is supplying oxygen through oxygen mask. If the cause is altitude it is also (naturally) recommended not to continue ascending. That goes for as long as the symptoms do not worsen, if they do it is highly recommended to descend to lower altitudes.

For reasons that still remain to be found high altitude sickness have been observed to affect men more than women.

Being a woman does not however prevent you from getting the sickness, it only lowers your risk. The same goes for being in good physique and health and not diving before ascending to high altitudes.