Simulation of Oxygen Uptake Kinetics in Exercise

The kinetics of oxygen uptake in exercise was simulated with assuming the kinetics of muscle oxygen uptake and considering the circulatory time delay. There were three phases in the simulated kinetics of oxygen uptake. The effects of the differences in time constant of cardiac output and muscle oxygen uptake and in venous blood volume on these phases of ox-ygen uptake kinetics were examined in the present simulation. Cardiac output had an effect on phase 1, muscle oxygen uptake on phase 2, and venous blood volume on phase 1 and 2. Furthermore the present simulation could become a possible way for estimating muscle ox-ygen uptake without previously assuming venous blood volume. Accordingly the simulation curve visually fitted for the measured oxygen uptake was obtained when parameters of venous blood volume and time constant of muscle oxygen uptake were controlled at 1. 5 I and 30 s, re-spectively. The estimated time constant of muscle oxygen uptake was slower than the mea-sured time constant of cardiac output. Thus the present result at the onset of step exercise could not suggest evidence supporting the transport limitation hypothesis of oxygen uptake kinetics