Final answer:
The partial pressure of oxygen (PO2) at sea level is 159 mmHg. Hemoglobin saturation is lower at high altitudes compared to sea level due to lower atmospheric pressure.
Step-by-step explanation:
The partial pressure of oxygen (PO2) at sea level is 159 mmHg.
An increase in altitude results in a decrease in atmospheric pressure. Although the proportion of oxygen relative to gases in the atmosphere remains at 21 percent, its partial pressure decreases. As a result, it is more difficult for a body to achieve the same level of oxygen saturation at high altitude than at low altitude, due to lower atmospheric pressure. In fact, hemoglobin saturation is lower at high altitudes compared to hemoglobin saturation at sea level.
For example, hemoglobin saturation is about 67 percent at 19,000 feet above sea level, whereas it reaches about 98 percent at sea level.