Open-loop analysis of circulatory system in awake live animals: relations between mixed venous saturation (SvO2) and hemodynamic parameters.

In order to derive quantitative relations between the mixed venous hemoglobin saturation (SvO2) and hemodynamic and metabolic parameters in awake live animals, biventricular bypass experiments were conducted in goats using a pair of pneumatic artificial hearts. The artificial hearts were used to bypass continuously the fibrillating ventricles, to control precisely the pump output, and to derive open-loop responses of the peripheral circulatory system. The specially developed reflection-type optical sensors were mounted on each artificial heart to measure continuously arterial and mixed venous SO2 and hemoglobin content ([Hb]), which in combination with pump output data oxygen consumption of the animal was derived on-line for a maximum duration of 40 days. The SvO2 sensitively reflected the changes in respiratory status. [Hb], pump output, and oxygen consumption. The SvO2 was linearly related to the oxygen consumption but showed nonlinear relation to the pump output. The exercise study revealed that the SvO2 level may be used to detect the anaerobic threshold. The SvO2 is a useful parameter to evaluate circulatory status of the patients.