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partial pressure

The pressure exerted by a single component of a mixture of gases, commonly expressed in mm hg or torr; for a gas dissolved in a liquid, the partial pressure is that of a gas that would be in equilibrium with the dissolved gas. Formerly, symbolised by p, followed by the chemical symbol in capital letters (e.g., pCO2, pO2); now, in respiratory physiology, P, followed by subscripts denoting location and/or chemical species (e.g., PCO2, PO2, PaCO2).