Jr

Qdt where Ci is the concentration of indicator. Hence the extravascular thermal volume (which is virtually equivalent to the extravascular lung water volume) is given by EVTV = CO(MTtT - MTtD).

Extravascular lung water can also be calculated in a different way from the exponential decay times, or downslope times (DSt), of semilogarithmic plots of the two dilution curves using the theory of Newman etaL (1951.). (Fig 1(b)). Newman and his colleagues modeled the central circulation of right heart, lungs, and left heart by linking three chambers in series through which fluid was pumped at a constant rate. They noted that when an indicator flowed through these chambers the downslope of the resulting dilution curve was determined by the flow and the volume of the largest chamber in the series only. Hence the volume of the largest mixing chamber between the point of injection and the point of detection is the product of the cardiac output and the downslope time of the indicator.

When this is applied to the central circulation, the largest mixing chamber for the diffusible indicator is the intra- and extravascular space in the lung (the pulmonary thermal volume (PTV)) and that for the non-diffusible indicator is the pulmonary intravascular space (pulmonary blood volume (PBV)):

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