APPLICATION OF EXPIRED GAS SIMULATION BY SYSTEM DYNAMICS TO CONSTANT WORK RATE EXERCISE

Abstract

PURPOSE To construct a system dynamics (SD) model with use of expired gas data obtained during an incremental exercise test and to simulate kinetics of VO2, VCO2 and VE during a constant exercise test used by the SD model. METHODS Five healthy males took part in this study. All subjects performed an incremental test to determine maximal oxygen uptake (VO2max) and anaerobic threshold (AT). Then, the subjects undertook three constant tests that consisted low work rate (80%AT), middle work rate (100%AT), high work rate (120%AT) by a cycle ergometer. In this modeling, it was assumed that 1) the behavior of VO2 and lactate (La) depends on exercise intensity, 2) VCO2 is the sum of metabolic VCO2 that stems from increased VO2 and VCO2 that is generated for buffering La, 3) VE is the sum of normal ventilation and hyperventilation that depends on respiratory compensation. Fitness of the model was examined by determination coefficient (r2) of simulated and measured VE, VO2 and VCO2. Robustness of simulation to the change in intensity was examined by a comparison of simulation residual to measurement of each constant test. The data of the incremental test were used for modeling, and data of constant tests for criteria of validity. RESULTS In all subjects, the goodness of fit index of the simulated VE, VCO2 and La to measured data for the incremental test were high (r2 > 0.90, P < .05), so that the SD model was verified. For simulation of each intensity constant test, simulated VE, VO2 and VCO2 were significantly fitted to the measurements for low, middle and high work rate constant tests (r2 > 0.90, P < .05). In comparison of residuals of simulated VE, VO2 and VCO2, there were not significant differences among all work rate constant tests, thereby indicating robustness of simulation. CONCLUSION The simulation of expired gas dynamics used the SD model was valid and robust to constant exercise.