From the Guidelines
At high altitude, decreased partial pressure of oxygen triggers several metabolic adaptations in the body to maintain adequate oxygen delivery and utilization. These adaptations are crucial for individuals, especially those with pre-existing conditions such as heart failure, as they are more susceptible to the physiological changes induced by high altitude exposure 1. The body's initial response to high altitude includes increased ventilation and heart rate to compensate for reduced oxygen availability, leading to respiratory alkalosis and hypoxic diuresis 1. Within hours to days, erythropoietin production increases, stimulating red blood cell production to enhance oxygen-carrying capacity. Some key metabolic changes that occur in response to high altitude and decreased partial pressure oxygen include:
- Increased 2,3-diphosphoglycerate (2,3-DPG) in red blood cells, which facilitates oxygen release to tissues
- Mitochondrial density increases in muscle cells to improve oxygen utilization efficiency
- Metabolic substrate preference shifts toward greater carbohydrate utilization, as glucose metabolism requires less oxygen than fat metabolism
- Increased expression of hypoxia-inducible factor (HIF), which activates genes involved in oxygen homeostasis
- Capillary density increases to improve oxygen delivery to tissues
- Enhanced production of antioxidant enzymes to combat increased oxidative stress It is essential to note that the degree of these adaptations can vary depending on individual factors, such as exercise tolerance at sea level, and certain medications, like angiotensin-converting enzyme inhibitors and angiotensin receptor blockers, can interfere with these physiological adaptation processes 1. Additionally, oxygen saturation at altitude can vary with age, sex, ethnic group, and degree of acclimatization to altitude, with native populations often having higher oxygen saturation levels than non-native individuals 1. Therefore, it is crucial to assess the safety of high altitude exposure for individuals, particularly those with pre-existing conditions, and consider their functional capacity and potential medication interactions to ensure optimal metabolic adaptations and minimize the risk of complications.
From the Research
Metabolic Changes at High Altitude
At high altitude, the decreased partial pressure of oxygen can lead to several metabolic changes, including:
- Increased glycolysis: The body relies more on anaerobic metabolism to produce energy, resulting in increased lactic acid production 2, 3.
- Increased glucose production: The liver increases glucose production to meet the energy demands of the body 4, 5.
- Decreased insulin sensitivity: The body becomes less responsive to insulin, making it harder for glucose to enter cells 5, 6.
- Increased fat breakdown: The body breaks down fat for energy, resulting in increased levels of free fatty acids in the blood 3, 4.
- Increased production of erythropoietin: The kidney produces more erythropoietin, which stimulates the production of red blood cells to carry more oxygen to the body's tissues 2, 5.
Physiological Responses
The physiological responses to high altitude include:
- Increased heart rate and blood pressure: The body tries to compensate for the lower oxygen levels by increasing blood flow to the body's tissues 3, 4.
- Increased ventilation: The body tries to take in more oxygen by increasing breathing rate 2, 5.
- Decreased oxygen delivery: The body's tissues receive less oxygen, leading to decreased energy production and increased fatigue 4, 6.
Treatment and Prevention
Treatment and prevention of high altitude illnesses, such as acute mountain sickness, include:
- Acetazolamide: A medication that helps increase oxygen delivery to the body's tissues and reduce symptoms of altitude sickness 2, 3, 4, 5, 6.
- Descent: The most effective treatment for severe altitude sickness is to descend to a lower altitude 3, 5, 6.
- Slow ascent: Gradually increasing altitude exposure can help the body adapt to the lower oxygen levels 2, 4, 5, 6.
- Oxygen supplementation: Providing additional oxygen can help increase oxygen delivery to the body's tissues 3, 5.