SULFHEMOLOGLOBINATED ERYTHROCYTES AS AN OPTICAL INTRAVASCULAR TRACER IN THE LUNG

Sulfhemoglobinated erythrocytes (SHb-RBC's) were examined for utility as an optical multiple indicator dilution tracer in lung studies. A de vice was developed to measure this tracer optically in flowing blood. Arterial blood was sampled from cannulated, anesthetized dogs and pump ed through the device that measured the optical density (OD) of blood at 620 nm. This system was calibrated for increasing SHb-RBC concentra tions using an unsteady-state indicator dilution procedure. Areas unde r optical density (DELTAOD) profiles were well correlated with injecte d SHb-RBC volumes using linear regression (r2 > 0.9). This linearity w as independent of blood oxygenation, hematocrit, or pH. In vivo lung i ndicator dilution studies in the intact dog were performed and compare d to radioisotope indicator studies using Cr-51 labeled erythrocytes. Coefficient of variation (CV) between the two curves was 0.065 under b aseline conditions, 0.085 for studies performed during hypoxia. and 0. 073 after pH was lowered. We conclude that this device linearly measur ed SHb-RBC content in whole blood and that SHb-RBC is as accurate a lu ng indicator dilution tracer as Cr-51-erythrocytes.