A novel geometric method for determining the time constant for oxygen uptake kinetics.

The kinetic response of oxygen uptake (V̇o₂) to transitions of exercise intensity is one of the important parameters of aerobic function. The typical kinetic response between two steady states can be reasonably well fitted with a mono-exponential function that has a time constant τV̇o₂. However, due to the variability of breath-by-breath measures of V̇o₂ determination of τV̇o₂ has usually required superimposition of repeated exercise protocols. We developed a novel geometric method of determining τV̇o₂ from the analysis of slopes and intercepts of a plot of cumulative oxygen uptake (cumV̇o₂) versus time for single exercise protocols. We used mathematical modeling to generate 3,600 series of breath-by-breath V̇o₂ measures versus time for various exercise protocols. To test whether our geometric method was robust to the presence of real-life variability, we applied random (Gaussian) variation to both the interval between breaths and to the measured values of V̇o₂. Our method derived values for τV̇o₂ that were accurate to within 1.5-3.5 s for both on- and off-transits and for models that represented healthy normal subjects as well as persons with cardiovascular disease. The coefficient of variation for multiple iterations of the method was &lt;10% as long as the signal-to-noise ratio was &gt;20:1. We present a novel geometric method for deriving the τV̇o₂ of oxygen uptake kinetics. This method uses analysis of the slopes and intercepts of a plot of cumulative V̇o₂ versus time and does not require multiple repetitions of the exercise protocol but still gives accurate estimates of τV̇o₂.<b>NEW &amp; NOTEWORTHY</b> We present a novel geometric method for deriving the τV̇o₂ of oxygen uptake kinetics. This method uses analysis of the slopes and intercepts of a plot of cumulative V̇o₂ versus time and does not require multiple repetitions of the exercise protocol but still gives accurate estimates of τV̇o₂.