Review Question - QID 107937

This vignette describes the development of respiratory alkalosis in an otherwise healthy man at high altitude due to decreased atmospheric pressure at high altitude, and thus a decreased partial pressure of alveolar oxygen, which leads to hypoxemia.

There are many common causes of hypoxemia: hypoventilation, diffusion limitation, shunt, V/Q mismatch, and environmental factors. An example of the latter is in high altitude setting, where the partial pressure of alveolar oxygen is lower. Hypoxemia triggers peripheral chemoreceptors that sends signals to the ventral medullary respiratory center to increase minute ventilation. This corrects the hypoxemia somewhat, but at the expense of hypocapnea. Tissue hypoxia ensues, resulting in systemic symptoms collectively termed "mountain sickness."

Incorrect Answers:
Answer 1: Pulmonary vessels vasoconstrict in response to hypoxia by the Euler-Liljestrand mechanism. This is a physiological response to alveolar hypoxia resulting in vasoconstriction in those blood vessels in an area of lower oxygen partial pressure. This redirects blood flow to areas of the lung that have a higher oxygen partial pressure.
Answer 3: Carbon dioxide does not increase due to high altitude.
Answer 4: This healthy male has no suggestion of disease that limits diffusion of gases, such as fibrosis.
Answer 5: An atrial septal defect can cause more pronounced hypoxemia, but there are no associations with structural heart disease and increased mortality in high-altitude settings.