Question

A patient flying to high altitude of 3700 m develops headache, nausea, dyspnea, and dizziness. What explains these symptoms?

• A. Hypoxia causing vasodilation
• B. Hypoxia causing vasoconstriction
• C. Metabolic acidosis causing edema
• D. High PO$_2$ causing vasoconstriction

Hint:

High altitude symptoms are due to hypoxia; cerebral hypoxia causes vasodilation and headache.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question explores the physiological basis for the symptoms of Acute Mountain Sickness (AMS) occurring at high altitudes.
Step 2: Detailed Explanation:

Environmental Stress: At 3700m, the atmospheric pressure is lower, leading to a decrease in the partial pressure of inspired oxygen. This results in hypoxemia.

Cerebral Response: The brain is highly sensitive to oxygen levels. In response to hypoxia, the cerebral blood vessels undergo vasodilation to increase blood flow and oxygen delivery to the neural tissues.

Symptom Mechanism: This cerebral vasodilation increases intracranial pressure, which is the primary cause of the characteristic "altitude headache" and dizziness. If severe, this can progress to High-Altitude Cerebral Edema (HACE).

Pulmonary Response: Interestingly, the lungs respond oppositely. Hypoxia in the lungs causes vasoconstriction (Hypoxic Pulmonary Vasoconstriction). This increases pulmonary artery pressure and can lead to High-Altitude Pulmonary Edema (HAPE), causing dyspnea.

Why B is incorrect: While vasoconstriction occurs in the lungs, it is the cerebral vasodilation that explains the dominant symptoms of headache and dizziness. Metabolic acidosis (Option C) does not occur initially; rather, hyperventilation causes a respiratory alkalosis.

Step 3: Final Answer:
The clinical symptoms of altitude sickness are primarily driven by hypoxia-induced cerebral vasodilation.