hapenpaine

Hapenpaine, or partial pressure of oxygen (PO2), is the pressure that oxygen would exert if it alone occupied the total pressure of a gas mixture. It is measured in millimeters of mercury (mmHg) or kilopascals (kPa) and is used to quantify the amount of dissolved oxygen in a gas or liquid. The concept distinguishes dissolved oxygen from the oxygen bound to hemoglobin; the dissolved portion is proportional to PO2 according to Henry's law, while total oxygen content also depends on hemoglobin saturation.

In humans, key PO2 values are used to describe oxygen availability in different contexts. Inspired PO2 in ambient air at sea level is about 159 mmHg. Alveolar PO2 (PAO2) is about 100 mmHg, reflecting gas exchange in the lungs. Arterial PO2 (PaO2) normally ranges roughly from 75 to 100 mmHg, while venous PO2 is around 40 mmHg. At higher altitudes or in lung disease, PaO2 can fall, leading to hypoxemia. Clinically, PaO2 is measured from arterial blood gas tests; noninvasive estimates rely on oxygen saturation methods but do not directly measure PaO2.

Factors affecting hapenpaine include altitude, inspired oxygen fraction (FiO2), barometric pressure, and the efficiency of gas exchange. Supplemental oxygen increases PaO2 and thus hapenpaine in the blood.

The alveolar gas equation relates PAO2 to FiO2, Pb (barometric pressure), PH2O (water vapor pressure), PaCO2, and the respiratory quotient: PAO2 ≈ FiO2 × (Pb − PH2O) − PaCO2/R. This framework aids assessment of respiratory function and detection of hypoxemia.

In Finnish medical literature, hapenpaine is commonly used to refer to the oxygen partial pressure in blood or breathing mixtures, particularly PaO2 in arterial blood.