Gas exchange in a three-compartment lung model analyzed by forcing sinusoids of N2O

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Abstract
A mathematical gas exchange model, using sinusoidal forcing functions of inert inspired gas (A. Zwart, R. C. Seagrave, and A. Van Dieren. J. Appl. Physiol. 41: 419#x2013;424, 1976), has been extended by us to include dead space (VD), a single alveolar compartment (VA) perfused with blood flow (Qp), and a shunt (Qs). In this new work we use N2O as the indicator gas in the mathematical model and in the experimental studies, in low enough concentrations [ or = 2 min-1. Theoretical results from the model are presented for a wide range of forcing frequencies between 2 x 10(-2) and 10 min-1 (sinusoid periods 30#x2013;0.1 min), and these show that VA, Qp, and VD/VT can all be measured by N2O forcing frequencies > or = 1 min-1. We also present results from five animal studies, with an experimental inspired gas forcing frequency range of 0.125 to 2 min-1, which show qualitative agreement with the predictions of the continuous ventilation model. During these animal studies both mass spectrometric N2O respiratory gas measurements and intravascular polarographic arterial and mixed venous blood N2O partial pressure measurements were made, and examples of these in vivo measurements are presented, together with examples of the calculations derived from them.

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