Diffusing capacity: Difference between revisions

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== Calculation ==

The diffusion capacity for oxygen <math>(D_{L_{O_2}})</math> is the proportionality factor relating the rate of oxygen uptake into the lung to the oxygen gradient between the capillary blood and the alveoli (per [[Fick's laws of diffusion]]). In [[respiratory physiology]], it is convenient to express the transport of gas molecules as changes in volume, since <math>{V_{O_2}}\propto {n_{O_2}}</math> (i.e., in a gas, a volume is proportional to the number of molecules in it). Further, the oxygen concentration ([[partial pressure]]) in the pulmonary artery is taken to be representative of capillary blood. Thus, <math>(D_{L_{O_2}})</math> can be calculated as the ratiorate ofthat theoxygen volume of the oxygenis taken up by the lung <math>(\dot{V}_{O_{2}})</math> divided by the oxygen gradient between the alveoli ("A") and the pulmonary artery ("a").

{{NumBlk|::|<math>D_{L_{O_2}} =\frac {\dot{V}_{O_{2}}} {P_{A_{O_2}} - P_{a_{O_2}}} \simeq \frac {\dot{V}_{O_{2}}} {P_{A_{O_2}} - P_{v_{O_2}}}</math> | {{EquationRef|1}} }}

::(For <math>\dot{V}</math>, say "V dot". This is the notation of [[Isaac Newton]] for a first derivative (or rate) and is commonly used in respiratory physiology for this purpose.)