The effects of sinusoidal linear drifts on the estimation of cardiorespiratory dynamic parameters during sinusoidal workload forcing: a simulation study.

This study aimed at investigating whether: 1) different sinusoidal linear drifts would affect the estimation of the dynamic parameters amplitude (A) and phase lag (φ) of minute ventilation (V˙), oxygen uptake, carbon dioxide production and heart rate (HR) sinusoidal responses when the frequency analysis technique (F) is performed; 2) the Marquardt-Levenberg non-linear fitting technique (ML) would provide more precise estimations of A and φ of drifted sinusoidal responses compared to F. For each cardiorespiratory variable, fifteen responses to sinusoidal forcing of different sinusoidal periods were simulated by using a first-order dynamic linear model. A wide range of linear drifts were subsequently applied. A and φ were computed for all drifted and non-drifted responses by using both F (A and φ) and ML (A and φ). For non-drifted responses, no differences between A vs A and φ vs φ were found. Whereas A and φ were affected by the sinusoidal linear drifts, A and φ were not. Significant interaction effects (technique x drift) were found for A (P <  0.001; ƞ > 0.247) and φ (P <  0.001; ƞ > 0.851). Higher goodness of fit values were observed when using ML for drifted V˙ and HR responses only. The present findings suggest ML as a recommended technique to use when sinusoidal linear drifts occur during sinusoidal exercise, and provide new insights on how to analyse drifted cardiorespiratory sinusoidal responses.