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As dictated by Dalton’s Law of partial pressures, the partial pressure of O2 is derived from multiplying its fractional concentration by the total pressure in the compartment under consideration. Figure 1 shows how O2 sequentially moves down its pressure gradient from moist inspired air to its site of utilization at the mitochondria. Thus, for dry air (20.93% O2) at sea level (barometric pressure 760 Torr) PO2 is 20.93/100 × 760 = 159 Torr. In its passage through the airways, air is warmed and moistened and this effectively reduces the PO2: 20.93/100 × (760 − 47) = 149 Torr [12]. As this air is inspired (PIO2) into the alveolar space, it is diluted with carbon dioxide and, depending on the respiratory exchange ratio (R = \( \dot{V} \)CO2/\( \dot{V} \)O2) volume may be lost (R < 1.0, rest, moderate exercise, eupnea) or gained (R > 1.0, heavy/severe exercise, hyperventilation). Alveolar PO2 (PAO2) is calculated using the...
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References
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Poole, D.C., Copp, S.W., Hirai, D.M., Musch, T.I. (2012). Oxygen Partial Pressure (PO2), in Heavy Exercise. In: Mooren, F.C. (eds) Encyclopedia of Exercise Medicine in Health and Disease. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-29807-6_159
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