What is the primary cause of a decrease in blood oxygen saturation at high altitudes?

The primary cause of a decrease in blood oxygen saturation at high altitudes is due to decreased ambient pressure. At higher altitudes, the atmospheric pressure lowers, which leads to a decrease in the partial pressure of oxygen in the air. This diminished pressure means that even though the percentage of oxygen in the air remains the same (approximately 21%), the amount of oxygen available to be inhaled and absorbed by the lungs decreases. As a result, less oxygen enters the bloodstream, leading to lower oxygen saturation levels.

While factors like increased carbon dioxide levels and changes in heart and breathing rates may contribute to the overall response to high altitude, they do not directly cause the primary issue of low blood oxygen saturation. The essential challenge at high altitudes primarily stems from the thin air and reduced pressure that limits oxygen availability for the body.