Influence of interalveolar diffusion on pulmonary gas exchange

This dissertation presents and analytic method to determine the extent to which interalveolar diffusion can influence pulmonary gas exchange in response to graded vascular embolization. The method shows that failure of inert gas techniques to detect microemboli is due to interalveolar diffusion of inert tracer gases, and demonstrates that microembolic involvement is detectable with the added use of the less diffusible stable isotopes 18O2 and 13CO2. An animal study utilizing two sets of physiologic/inert gas pairs (18O2/acetylene, and 13CO2/dimethyl ether) is presented. Spherical polystyrene beads (diameter 50-500 µm) were injected into anesthetized dogs to induce microembolism. Gas exchange was assessed using the synchronous tracer injection method. In addition to being consistent with the model predictions of the interalveolar, diffusion, the results show sufficient separation in the two gas pairs to suggest feasibility for utilizing the method as a noninvasive means for quantitating both embolic dimension and the extent of involvement throughout the lung. Implications for involvement in human subjects are discussed.