Which of the following is needed to calculate alveolar oxygen tension?

To calculate alveolar oxygen tension (PAO2), the most relevant factor to consider is the fraction of inspired oxygen (FiO2), which represents the concentration of oxygen in the air we breathe. In addition to that, barometric pressure (BP) is also crucial since it influences the amount of oxygen available for the body depending on atmospheric conditions.

The equation to calculate PAO2 typically follows the formula:

[ PAO2 = (FiO2 \times (BP - PH2O)) - (PaCO2 / RQ) ]

where PH2O is the partial pressure of water vapor and RQ is the respiratory quotient. This demonstrates how PAO2 is significantly affected by both the fraction of inspired oxygen and the barometric pressure.

Thus, having both BP and FiO2 allows for a comprehensive understanding of the oxygen available for transfer to the bloodstream in the alveoli, making this choice the correct answer for determining alveolar oxygen tension.