Key result
During step-loaded exercise in a calf, mixed venous oxygen saturation decreased from 59.6% to 52.2% as cardiac output increased from 8.9 to 11.4 L/min, demonstrating a linear correlation.
Mixed venous oxygen saturation closely tracks cardiac output changes during exercise without conspicuous time delay, making it a promising parameter for physiologic control of a total artificial heart.
SvO2 may guide total artificial heart control during exercise; animal data leave human translation open.
Mixed venous oxygen saturation (SvO2) has been proposed as one of the suitable parameters for physiologic control of a total artificial heart (TAH). To establish the practical application of SvO2, we investigated the response of cardiac output (CO) and SvO2 to step-loaded exercise. A normal calf was surgically equipped with an ultrasonic flowmeter probe and an oximetry catheter in the pulmonary artery to measure CO and SvO2, respectively. Three stage step treadmill exercise tests (1, 2, and 4 km/h) were performed three times. While CO increased from 8.9 L/min at preexercise level to 9.7, 10.2 and 11.4 L/min at 1, 2, and 4 km/h, respectively, SvO2 decreased from 59.6% to 56.8, 55.3, and 52.2%, respectively. There existed a linear correlation between the magnitude of changes in CO and SvO2. CO and SvO2 exhibited a similar course of change, expressing an inverted exponential curve. The time constant of SvO2 was from 19 to 35 seconds, whereas that of CO was from 21 to 39 seconds. We conclude that SvO2 changes in close association with CO during exercise and has good potential to be a parameter for physiologic control of a TAH, by reflecting the recipient's CO demand without conspicuous time delay.
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Nakamura et al. (2000) studied Evaluation for total artificial heart control (n=1). Step-loaded treadmill exercise vs. Preexercise level was evaluated on Response of cardiac output (CO) and mixed venous oxygen saturation (SvO2). During step-loaded exercise in a calf, mixed venous oxygen saturation decreased from 59.6% to 52.2% as cardiac output increased from 8.9 to 11.4 L/min, demonstrating a linear correlation.
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