Pulmonary gas-exchange analysis by using simultaneous deposition of aerosolized and injected microspheres

Numerical methods for determining end-capillary gas contents for ventilatio n-to-perfusion ratios were first developed in the late 1960s. In the 1970s these methods were applied to validate distributions of ventilation-to-perf usion ratios measured by the multiple inert-gas-elimination technique. We c ombined numerical gas analysis and fluorescent-microsphere measurements of ventilation and perfusion to predict gas exchange at a resolution of simila r to 2.0-cm(3) lung volume in pigs. Oxygen, carbon dioxide, and inert gas e xchange were calculated in 551-845 compartments/animal before and after pul monary embolization with 780-mu m beads. Whole lung gas exchange was estima ted from the perfusion- and ventilation-weighted end-capillary gas contents . Before lung injury, no significant difference existed between microsphere -estimated arterial PO2 and PCO2 and measured values. After lung injury, th e microsphere method predicted a decrease in arterial PO2 but consistently underestimated its magnitude. Correlation between predicted and measured in ert gas retentions was 0.99. Overestimation of low-solubility inert gas ret entions suggests underestimation of areas with low ventilation-to-perfusion ratios by microspheres after lung injury. Regional deposition of aerosoliz ed and injected microspheres is a valid method for investigating regional g as exchange with high spatial resolution.