Continuous Measurement of Oxygen Delivery and Oxygen Consumption in Awake Live Animals

Abstract

The spectrophotometric reflection method can provide accurate and rapid measurement of hemoglobin oxygen saturation (SO₂) by utilizing optical absorption differences of oxy- and deoxy-hemoglobin (Figure 1, Van Assendelft, 1970) and scattering characteristics at the red cell-plasma interface. Based on the reflection technique, various oximeters have been developed including the fiber-optic catheter (Cole et al., 1972;Baele et a]., 1982), catheter-tip oximeters (Yee et al., 1977; Schmitt et al., 1986), and finger tip pulse oximeters (Mendelson et al., 1983). Though these systems can provide continuous and accurate measurement of hemoglobin oxygen saturation in various clinical settings at the bed-side, there is not yet a clinically reliable in vivo oximeter that can provide simultaneous measurements of both hemoglobin content ([Hb]) and oxygen saturation. Thus, when measurement of cardiac output or oxygen consumption is required in the clinical setting, the blood is analyzed for its hemoglobin content and then the oxygen content derived. Also, the measurement of SO₂ is affected by the variations in the hematocrit which exist from person to person and which occur, for example, during cardio-pulmonary bypass, due to hemodilution. Calibration is thus necessary as the hematocrit shift occurs.