Oximetry

Oximetry is the estimation of per cent oxygen saturation of blood by photometric means. Incident light may be reflected from a vascular bed or cuvette and the reflected light measured, or the transmitted light may be measured to yield the required data. Theoretically, transillumination lends itself to absolute measurement with a two-color system, whereas reflection oximetry requires three colors. The instrumentation described employs two colors along with an alternating light source to allow ac amplification. An analogue computer provides a continuous ratio of the corresponding two currents recorded by an ink-writing milliameter. The over-all response to a step change has a period of less than 0.5 seconds and is considered rapid enough for clinical dye curve studies. There is reason to believe that the deficient long-term stability of the photocells limits function as an absolute oximeter.