How Our Bodies Respond to Higher Altitudes

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As we gain more and more elevation, air pressure decreases. A decrease in air pressure means that there are fewer oxygen molecules. After a certain altitude, there just isn't enough oxygen in the air to sustain life. If we kept breathing in the same manner we do at sea level, we wouldn't be able to live. To counteract lowered oxygen levels, our body initiates a specific pulmonary response. This response alters several bodily functions in an effort to obtain more oxygen.

Physiological problems we face at high altitude (2400m or more above sea level)

  • hypoxia (lack of oxygen): the primary cause of all problems at high altitude, hypoxia forces the body to make adaptations to receive, absorb, and deliver more oxygen.
  • lowered % saturation of hemoglobin with oxygen: a result of hypoxia, lowered % oxygen saturation in hemoglobin
  • low temperature: the low temperature at high altitudes naturally works to slow down heartbeat rate despite the low level of oxygen in the atmosphere. The body must overcome this to deliver sufficient oxygen to body tissues.

How we respond to them
Hemoglobin oxygen saturation based on 2,3-DPG levels

  • hyperventilation - the primary response to decreasing oxygen levels, hyperventilation is the automatic increase in breathing rate to sustain sufficient oxygen levels for survival. Prolonged hyperventilation can lower carbon dioxide levels (lost during exhalation), impairing respiratory function.
  • pulmonary hypertension - the constriction of pulmonary arterioles leads to pulmonary hypertension (high blood pressure of the arteries). Pulmonary hypertension causes blood vessels to be more permeable, leading to fluid leakage and ultimately edema.
  • production of reactive radical species - the body's efforts to sustain high energy output despite low oxygen levels results in the production of highly reactive radical species, which are destructive to cells.
  • release of EPO (erythropoietin) - hormone that stimulates the production of erythrocytes in bone marrow, increasing the amount of oxygen that can be carried per volume of blood.
  • diuresis - increases oxygen carrying capability by increasing blood concentration.
  • increased production of 2,3-DPG: explained below

Increasing Production of 2,3-DPG

2,3-DPG is an organic phosphate in the red blood cells that controls the movement of oxygen from red blood cells to tissues. The amount of 2,3-DPG in the red blood cells determines how much and how easily hemoglobin gives up oxygen to the body tissues. The more 2,3-DPG there is, the more oxygen is released by hemoglobin to the tissues. 2,3-DPG binds to hemoglobin, lowering its affinity for oxygen. 2,3-DPG can also be released into body tissues along with oxygen, increasing the efficiency of glucose metabolism and the pathway’s dependence on oxygen. In this way, 2,3-DPG serves to relieve oxidative stress.

Increasing the number of 2,3-DPG molecules in the blood is the body’s typical response to hypoxic environments (low oxygen). There is a direct relationship between the amount of 2,3-DPG a person produces and the oxygen content of his or her blood. In people with low oxygen content, there is an increase in 2,3-DPG to deliver more oxygen to the tissues. The body’s increased production of 2,3-DPG works to alleviate the problems associated with poor oxygenation. At the same time, because 2,3-DPG binds to sites on the hemoglobin molecule, there are fewer sites for oxygen to bind. Therefore, as there is more 2,3-DPG, the percent oxygen saturation of hemoglobin decreases. Despite this, 2,3-DPG still proves to have a positive impact on oxygen delivery.

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