Partial pressure of oxygen in the lungs

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Partial pressure of oxygen in the lungs

Partial pressure of inspired oxygen follows Dalton’s law: the partial pressure contributed by a gas equals its fraction in the mixture times the total pressure. Therefore, the inspired O2 partial pressure is the fraction of inspired oxygen (FiO2) multiplied by the barometric pressure (PB). This product form correctly scales with how much oxygen is present and how high the ambient pressure is. For a quick check, at sea level PB is about 760 mmHg and FiO2 is 0.21, giving roughly 160 mmHg for PIO2. In reality, humidity and CO2 are handled differently in the alveolar gas equation, but for the inspired oxygen itself, multiplying FiO2 by PB is the standard relationship.

Partial pressure of inspired oxygen follows Dalton’s law: the partial pressure contributed by a gas equals its fraction in the mixture times the total pressure. Therefore, the inspired O2 partial pressure is the fraction of inspired oxygen (FiO2) multiplied by the barometric pressure (PB). This product form correctly scales with how much oxygen is present and how high the ambient pressure is. For a quick check, at sea level PB is about 760 mmHg and FiO2 is 0.21, giving roughly 160 mmHg for PIO2. In reality, humidity and CO2 are handled differently in the alveolar gas equation, but for the inspired oxygen itself, multiplying FiO2 by PB is the standard relationship.

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