What is the paial pressure for oxygen in the inspired air?
**Core Concept**
The partial pressure of oxygen in inspired air is a crucial parameter in respiratory physiology, reflecting the amount of oxygen available for gas exchange in the lungs. It is influenced by atmospheric pressure and the percentage of oxygen in the air.
**Why the Correct Answer is Right**
The partial pressure of oxygen (pO2) in dry air at sea level is approximately 159 mmHg, but since we breathe humidified air, the partial pressure of water vapor (47 mmHg) must be subtracted from the total atmospheric pressure (760 mmHg), resulting in a partial pressure of oxygen of about 160 mmHg * 0.21 = 100 mmHg * (760-47)/760, which simplifies to approximately 100-110 mmHg when considering the fraction of oxygen in the air (0.21) and adjusting for humidification.
**Why Each Wrong Option is Incorrect**
**Option A:** This option might represent a miscalculation or misunderstanding of the atmospheric conditions or fraction of oxygen.
**Option B:** Similarly, this could result from an error in calculating the partial pressure or not accounting for humidification.
**Option C:** This might be a confusion with another physiological parameter or a miscalculation of oxygen's partial pressure.
**Option D:** This could be due to incorrect application of the atmospheric pressure or oxygen fraction.
**Clinical Pearl / High-Yield Fact**
Remembering that the partial pressure of oxygen in inspired air is about 100-110 mmHg at sea level is crucial for understanding gas exchange and interpreting blood gas results.
**Correct Answer:** D. 104 mmHg