Pulmonary blood flow and tissue volume: model analysis of rebreathing estimation methods.

As the basis for comparing rebreathing methods of estimating pulmonary blood flow (Q) and tissue-capillary volume (Vtc), we use a dynamic mass-balance model for gas species having different physicochemical properties (e.g., He, CO, C2H2). The model accounts for the effects of ventilation and perfusion inhomogeneities, breathing pattern variation, lung and rebreathing-bag volumes, and recirculation. Also, we examine the variability of the estimates caused by random error. In addition to analyzing two well-known methods, we show how an appropriate synthesis of these methods can lead to improved estimates.