DELAY-TIME ADJUSTMENTS TO MINIMIZE ERRORS IN BREATH-BY-BREATH MEASUREMENT OF VO(2) DURING EXERCISE

If the delay time between gas concentration and flow signals is not ad equately corrected during breath-by-breath analysis of expired gas, an error in calculation of oxygen consumption (Vo(2)) will result. To ex amine the frequency and delay time dependences of errors in Vo(2) meas urement, six healthy men exercised at 100, 200, and 250 W on a cycle e rgometer while breath-by-breath assessment of Vo(2) was made simultane ously with collection of expired air. Subjects breathed first at norma l rates (15-30 breaths/min) and then at 70 breaths/min. Each subject p erformed each level of exercise twice by using erroneous values for th e delay time between gas concentration and flow signals. At normal bre athing frequencies, errors in Vo(2) measurement were +/-10% over the f ull range of delay times used, and the errors were not tightly correla ted with variations in delay times from optimum. However, at 70 breath s/min, errors approached +/-30% as the variations in delay times devia ted +/-0.1 s from the optimal, and the errors were highly correlated w ith the variations in delay times. We conclude that there is greater p otential for errors in Vo(2) measurement with incorrect delay time at higher breathing frequencies. These findings suggest that the optimal delay time for breath-by-breath systems should be adjusted by using hi gh breathing frequencies.