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

Abstract

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 <10% as long as the signal-to-noise ratio was >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.NEW & NOTEWORTHY 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.