An optical multiple indicator dilution technique to measure lung permeability-surface area: calibration and baseline measurement

A device was designed to measure the change in optical density (ΔOD) of blood at selected wavelengths as a function of the concentration of optically absorbing multiple indicator dilution (MID) tracers. The optical MID (OMID) tracers selected for this measurement device and their corresponding wavelengths are the following: indocyanine green(ICG)-bound albumin measured at 820 nm, sulfhemoglobinated erythrocytes (Shb-RBC´s) measured at 620 nm, and 1,2-propanediol measured at 9.55 μm. Arterial blood from cannulated anesthetized dogs was circulated through an extracorporeal flow-through circuit which included this ΔOD measurement device. Calibration of the 820 nm and 620 nm channels produced r² of greater than 0.95 for the optical density-tracer mass regressions. The propanediol measurement channel (9.55 μm) was also linearly calibrated. An in vivo optical MID study was performed and compared to a radioisotope MID study. Lung vascular permeability-surface area (PS) values calculated using the two methods were 5.76 and 5.73 mL/s. It is concluded that this OMID technique is an acceptable alternative to radioisotope MID studies