Physical stressors pt.2

Defined as elevations above approximately 2,500 meters (8,000 feet).
Home to approximately 140 million people globally.
Physiological effects of high altitude can be detected; human settlements extend up to 5,000 meters (16,000 feet).
Certain jobs permit working at 5,800 meters, albeit with significant health costs.
Noted populations include those in the Andes, Himalayas, and Ethiopian Highlands.

Major stressors include:
- UV Radiation: Increased exposure at high elevation.
- Cold and Arid Conditions: Leads to reduced comfort and challenges for survival.
- Low Soil Quality: Poses risks to local food production.
- Hypoxia: Characterized by low oxygen availability; percentage of O2 in the air remains constant at 21%, but the number of molecules per unit volume decreases significantly at high altitudes due to lower atmospheric pressure.

Arterial oxygen saturation levels vary with altitude:
- At low altitude (0 m): 98% saturation.
- At 3,000 m: Drops to 90% saturation.
Key data points extracted from physiological figures (e.g., partial pressure of oxygen, arterial blood saturation %).
Average arterial blood saturation decreases substantially against increasing elevation and decreasing barometric pressure.

Increased Breathing Rate: Known as hyperventilation, resulting in increased air intake in lungs but excess carbon dioxide release.
- CO₂ accumulation leads to carbonic acid formation, breaking down into bicarbonate and H⁺ ions.
- Increased blood pH may result in respiratory alkalosis.
- The brain responds to decreased CO₂ by slowing breathing, while kidneys work to excrete excess bicarbonate.
- This process can be summarized:
  ext{CO}2 + ext{H}2 ext{O}
  ightarrow ext{H}2 ext{CO}3
  ightarrow ext{HCO}_3^- + ext{H}^+

Some observed adaptations include:
- Increased Heart Rate: Initially increases, managed primarily by the body to adjust to lower oxygen levels.
- Increased Stroke Volume: Stroke volume remains higher than at sea level, improving blood circulation.
- Increased RBC Count: Stimulation of erythropoietin leads to red blood cell and hemoglobin production, increasing blood viscosity (risk factors include stroke and venous thromboembolism).
- Discussed controversial treatments such as venesectomy.

Initial physiological response includes increasing active capillaries in lungs, which act as a pulmonary defense mechanism.
Observed systematic vasodilation in systemic circulation and vasoconstriction in pulmonary circulation enhances oxygen transport efficiency.

Acute Mountain Sickness (AMS) occurs due to rapid ascent. Symptoms include:
- Shortness of breath
- Nausea and vomiting
- Fatigue
- Headaches
- Insomnia

High Altitude Cerebral Edema (HACE):
- Condition characterized by fluid accumulation in the brain, leading to:
- Headaches
- Disorientation
- Loss of coordination
- Memory loss
- Psychosis and coma
- Ataxia
High Altitude Pulmonary Edema (HAPE):
- Increased blood pressure among pulmonary vessels causes fluid buildup in alveoli, resulting in:
- Chest tightness
- Persistent cough
- Feelings of suffocation.

Mechanisms aim to improve oxygen delivery, demonstrated by increases in:
- Basal Metabolic Rate (BMR)
- Ventilation rates
- RBC production
- Capillarization.
Despite acclimatization efforts, risks of acute or chronic mountain sickness persist.

Geographically located in regions of Ecuador, Peru, and Bolivia among the Quechua population.
Notable physiological traits include:
- Short stature with “barrel-shaped” chests and increased lung volume.
- Diminished sensitivity to hyperventilation; however, pulmonary hypertension reported.
- Larger heart size, notably larger right ventricle compared to the left ventricle.
- Higher RBC and hemoglobin concentrations, confirming a greater oxygen-carrying capacity.

Sherpa tribe (Nepal in Himalayas) occupies altitudes of 4,850-5,450 m (15,900-17,900 ft).
Physiological comparisons indicate:
- Similar hemoglobin concentrations to sea-level populations, yet lower than Andean counterparts.
- Compromised arterial O₂ saturation levels resulting in lower hemoglobin.
- Unique characteristics include high resting ventilation rates and remarkable adaptation avoiding hypoxic pulmonary vasoconstriction, supported by high levels of nitric oxide (NO) aiding vasodilation.
- Increased capillary density and blood flow compensation for low levels of O₂.

Key differences were highlighted between Tibetan, Andean, and general Himalayan populations:
- Ventilation Rates: Tibetan populations exhibit increased ventilation rates compared to lower levels in Andean groups and more barrel-shaped chest structures.
- O₂ Concentration: Tibetans show lower hemoglobin concentrations but more efficient oxygen use compared to Andean populations.
- Blood Flow: Varied responses relative to blood flow to the brain and differences in pulmonary dynamics.

Deliveries at high altitude linked to low birth weights due to intrauterine growth restrictions.
Uterine artery adaptations noted through diameter expansions due to greater vascularization, directly impacting placental oxygen delivery.

Use of unprocessed coca leaves in indigenous Andean cultures serves as a cultural adaptation mechanism, providing heat retention, mild stimulant effects, and sustaining hunger.
- Contains compounds like alkaloids that support acclimatization practices.
Nutritional aspects include vitamins A and B and essential minerals aiding in mitigating symptoms related to acute mountain sickness.

Emphasis on the physiological nature of high altitude adaptations with significant developmental and cultural considerations observed throughout various high-altitude populations.
Highlighted natural selection and existing population differences in adaptations as crucial factors in comprehending human biological diversity in stressing environments.