Physiological response to high altitude

• At sea level the atmospheric pressure is 1 (760 mmHg)

• As we ascend up to mountain and aircraft travelling the pressure decreases

• Causes Hypoxic hypoxia results in acute mountain sickness

Alveolar PO2 at Different Elevations

Acclimatization to Low PO2• Increased Pulmonary Ventilation— Role of Arterial Chemoreceptors.

• Increased diffusing capacity of the lungs • Increase in Red Blood Cells and Hemoglobin Concentration• Increased vascularity of the peripheral tissues• Increased ability of the tissue cells to use oxygen despite low PO2

Natural Acclimatization of Native Human Beings Living at High Altitudes

• Starts from infancy• Increase in chest wall• greater quantity of RBC & hemoglobin

Effect of Breathing Pure Oxygen onAlveolar PO2 at Different Altitudes

Acute Effects of Hypoxiabegins at about 12,000 feet, are • Drowsiness• Headache• Lassitude • Mental and muscle fatigue• Nausea and euphoria

above 18,000 feet twitching or seizures

above 23,000 feet in the unacclimatized person, in coma, followed by death.

Acute Mountain Sickness

• Acute cerebral edema• Acute pulmonary edema

Acute Mountain SicknessFeatures:• Dyspnea at rest• Inability to walk• Cyanosis• Headache• Congestion of cheat• Cough with blood in the sputum• Lack of consciousness

Prevention:• Slow ascent to facilitate acclimatization• Breathing oxygen• Recognition of symptoms early• Descending to lower altitude to sleep

Chronic Mountain Sickness• Red cell mass and hematocrit become high

• Pulmonary arterial pressure becomes elevated even more than the normal elevation that occurs during acclimatization

• Right ventricular hypertrophy

• Peripheral arterial pressure begins to fall

• Congestive heart failure

• Death occurs unless the person is removed to a lower altitude.

Decompression during aircraft

Sudden decrease in pressure leads to hypoxia

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