Makindo Medical Notes.com

Overview of High Altitude Physiology

High altitude physiology studies the body's adaptations and responses to environments with reduced oxygen availability, typically at elevations above 2,500 meters (8,200 feet). Understanding these physiological changes is crucial for preventing and managing altitude-related illnesses.

Physiological Responses to High Altitude

• Hypoxia:
  • Reduced oxygen availability due to lower atmospheric pressure.
  • Leads to decreased arterial oxygen saturation and partial pressure of oxygen (PaO₂).
• Respiratory Changes:
  • Hyperventilation: Increased breathing rate to enhance oxygen intake and carbon dioxide elimination.
  • Respiratory alkalosis due to decreased CO₂ levels, which can be compensated by renal bicarbonate excretion over time.
• Cardiovascular Changes:
  • Increased heart rate and cardiac output to improve oxygen delivery to tissues.
  • Enhanced pulmonary arterial pressure to facilitate oxygen uptake in the lungs.
• Hematological Changes:
  • Increased erythropoiesis, leading to higher red blood cell (RBC) count and haemoglobin concentration.
  • Enhanced oxygen-carrying capacity of the blood.

Acclimatization

• Short-term Acclimatization:
  • Occurs within days to weeks of exposure to high altitude.
  • Involves increased ventilation, enhanced cardiac output, and improved oxygen delivery to tissues.
• Long-term Acclimatization:
  • Develops over weeks to months.
  • Includes increased RBC mass, greater capillary density in tissues, and improved mitochondrial efficiency for oxygen utilization.

Altitude-related Illnesses

• Acute Mountain Sickness (AMS):
  • Symptoms: Headache, nausea, dizziness, fatigue, and sleep disturbances.
  • Usually occurs within 6-24 hours of ascent and typically resolves with acclimatization or descent.
  • Prevention: Gradual ascent, adequate hydration, and possibly prophylactic medications like acetazolamide.
• High-Altitude Pulmonary Edema (HAPE):
  • Symptoms: Shortness of breath, cough, chest tightness, and frothy sputum.
  • Results from increased pulmonary artery pressure leading to fluid accumulation in the lungs.
  • Treatment: Immediate descent, oxygen therapy, and medications such as nifedipine.
• High-Altitude Cerebral Edema (HACE):
  • Symptoms: Severe headache, confusion, ataxia, and altered mental status.
  • Results from increased intracranial pressure due to fluid leakage in the brain.
  • Treatment: Immediate descent, oxygen therapy, and dexamethasone.

Prevention and Management

• Gradual Ascent:
  • Ascending slowly to allow time for acclimatization.
  • Recommended rate: No more than 300-500 meters (1,000-1,600 feet) per day above 3,000 meters (10,000 feet).
• Hydration and Nutrition:
  • Adequate fluid intake to prevent dehydration.
  • Balanced diet to support increased metabolic demands.
• Medications:
  • Acetazolamide: Enhances acclimatization by inducing metabolic acidosis, stimulating ventilation.
  • Dexamethasone: Used to prevent and treat AMS and HACE.
  • Nifedipine: Used to prevent and treat HAPE by reducing pulmonary artery pressure.

Research and Future Directions

• Ongoing studies aim to better understand genetic and molecular mechanisms underlying acclimatization and susceptibility to altitude-related illnesses.
• Development of more effective prevention and treatment strategies for altitude-related illnesses.

Summary

High altitude physiology encompasses the body's adaptations to reduced oxygen availability, including respiratory, cardiovascular, and hematological changes. Acclimatization helps mitigate the effects of hypoxia, but rapid ascent can lead to altitude-related illnesses such as AMS, HAPE, and HACE. Prevention strategies include gradual ascent, hydration, and prophylactic medications. Understanding these physiological responses and implementing appropriate measures can help prevent and manage the adverse effects of high altitude exposure.