A tidal breathing model for the multiple inert gas elimination technique

The tidal breathing lung model described for the sine-wave technique (D. J. Gavaghan and C. E. W. Hahn. Respir. Physiol. 106: 209-221, 1996) is genera lized to continuous ventilation-perfusion and ventilation-volume distributi ons. This tidal breathing model is then applied to the multiple inert gas e limination technique (P. D. Wagner, H. A. Saltzman, and J. B. West. J. Appl . Physiol. 36: 588-599, 1974). The conservation of mass equations are solve d, and it is shown that 1) retentions vary considerably over the course of a breath, 2) the retentions are dependent on alveolar volume, and 3) the re tentions depend only weakly on the width of the ventilation-volume distribu tion. Simulated experimental data with a unimodal ventilation-perfusion dis tribution are inserted into the parameter recovery model for a lung with 1 or 2 alveolar compartments and for a lung with 50 compartments. The paramet ers recovered using both models are dependent on the time interval over whi ch the blood sample is taken. For best results, the blood sample should be drawn over several breath cycles.