A non-invasive determination of lung perfusion compared with the direct Fick method.

In 5 young pigs (7--9 kg each) data on effective lung perfusion were obtained using a sinusoidal forcing function in the inspired halothane concentration. These data were compared with the cardiac output measured by the direct Fick method for oxygen, corrected for venous admixture. To produce different levels of cardiac output during each experiment the respiratory and circulatory conditions were changed. For the 5 experiments taken together, the mean of the ratios between the non-invasively obtained effective lung perfusion and the venous admixture corrected Fick data was 1.01 (SD = 0.14, n = 55) with r = 0.92.