Final answer:
As altitude increases, the atmospheric pressure decreases, resulting in a decrease in the partial pressure of gases in the atmosphere. This makes it more difficult for the body to achieve the same level of oxygen saturation at high altitudes. The percentages of gases in the atmosphere remain constant, but their partial pressures change with altitude.
Step-by-step explanation:
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.
For example, hemoglobin saturation is about 67 percent at 19,000 feet above sea level, whereas it reaches about 98 percent at sea level. While the percentages of the gases in the atmosphere remain constant, the partial pressure of the gases changes with altitude because the atmospheric pressure decreases.
The partial pressure of a gas in the atmosphere can be calculated using the ideal gas law: P = (Patm) X (percent content in mixture). At high altitudes, Patm decreases, causing the partial pressure of all gases in the atmosphere to decrease.