The “independent breath” algorithm: assessment of oxygen uptake during exercise

Reduction of noise of breath-by-breath gas-exchange data is crucial to improve measurements. A recently described algorithm (“independent breath”), that neglects the contiguity in time of breaths, was tested.

Oxygen, carbon dioxide fractions, and ventilatory flow were recorded continuously over 26 min in 20 healthy volunteers at rest, during unloaded and moderate intensity cycling and subsequent recovery; oxygen uptake (\(\dot {V}{{\text{O}}_{\text{2}}}\)) was calculated with the “independent breath” algorithm (IND) and, for comparison, with three other “classical” algorithms. Average \(\dot {V}{{\text{O}}_{\text{2}}}\) and standard deviations were calculated for steady-state conditions; non-linear regression was run throughout the \(\dot {V}{{\text{O}}_{\text{2}}}\) data of the transient phases (ON and OFF), using a mono-exponential function.

Comparisons of the different algorithms showed that they yielded similar average \(\dot {V}{{\text{O}}_{\text{2}}}\) at steady state (p = NS). The standard deviations were significantly lower for IND (post hoc contrasts, p < 0.001), with the slope of the relationship with the corresponding data obtained from “classical” algorithms being < 0.69. For both transients, the overall kinetics (evaluated as time delay + time constant) was significantly faster for IND (post hoc contrasts, p < 0.001). For the ON transient, the asymptotic standard errors of the kinetic parameters were significantly lower for IND, with the slope of the regression line with the corresponding values obtained from the “classical” algorithms being < 0.60.

The “independent breath” algorithm provided consistent average O₂ uptake values while reducing the overall noise of about 30%, which might result in the halving of the required number of repeated trials needed to assess the kinetic parameters of the ON transient.