Density indicator method to measure pulmonary blood flows.
The injection of plasma, saline, or erythrocyte (RBC) concentrate into the pulmonary circulation produces a change in the gravimetric density of the blood outflow similar to the dilution curve of dye. We used an improved density-measuring system to assess the flow of these density indicators through the lung in vivo and in vitro perfused dog lobe. From the in vitro density-dilution curves of plasma and RBC concentrate we calculated the pulmonary flow rate and found it to be 1.04 +/- 0.02 (SD) times the measured one. The outflow-dilution curves of gravimetric density were not as broad as those of optical density following in vivo injection of plasma bolus containing indocyanine green, and the gravimetric measurements dipped to base line, whereas the optical measurement did not. The density-dilution curves of isotonic saline injection are similar to that of plasma. Following injection of RBC concentrates with the dye, density changes in the pulmonary outflow lag behind the emergence of the dye. This was presumably related to RBC aggregation in the concentrates. In reference to the injected plasma, no loss in the density indicators for saline and RBC injection was observed. Based on these results and the similarity of the density indicators to the blood, we conclude that the plasma and isotonic saline are good density indicators to be used for the determination of pulmonary blood flows.