Final answer:
At sea level, the maternal partial pressure of oxygen (PO2) is calculated to be 160 mm Hg, while in the alveoli, it is approximately 110 mm Hg due to the mixture with residual air. At high altitudes, the partial pressure of oxygen decreases despite a constant oxygen concentration, causing lower hemoglobin saturation and diminished oxygen transport in the bloodstream.
Step-by-step explanation:
The partial pressure of oxygen (PO2) in the maternal blood at sea level is a measure of the amount of oxygen available for exchange in the lungs. At sea level, the pressure of the atmosphere is 760 mm Hg, and dry air contains 20.9% oxygen. Using these values, we calculate the partial pressure of oxygen as:
PO2 = (760 mm Hg) (0.21) = 160 mm Hg.
In the alveoli of the lungs, however, the PO2 is reduced due to the mixing of inspired air with residual air after exhalation. Taking into account a respiratory quotient (RQ) of 0.8 and an alveolar PCO2 of 40 mm Hg, we can approximate the alveolar PO2 by calculating:
alveolar PO2 = inspired PO2 - (PCO2/RQ)
alveolar PO2 = 160 mm Hg - (40 mm Hg / 0.8) = 110 mm Hg.
At high altitudes, even though the concentration of oxygen remains constant at 21%, the partial pressure of oxygen decreases due to the lower atmospheric pressure (Patm). This makes it more difficult to achieve the same oxygen saturation as at sea level. Hemoglobin saturation is significantly lower at high altitudes, affecting how much oxygen gets carried in the bloodstream.