Effects of inspiratory loading on the chaotic dynamics of ventilatory flow in humans.

Human ventilation at rest exhibits complexity and chaos. The aim of this study was to determine whether suprapontine interferences with the automatic breathing control could contribute to ventilatory chaos. We conducted a post hoc analysis of a previous study performed in awake volunteers exhibiting cortical pre-motor potentials during inspiratory loading. In eight subjects, flow was recorded at rest, while breathing against inspiratory threshold loads (median 21.5 cm H(2)O) and resistive loads (50 cm H(2)Ol(-1)s(-1)) loads, and while inhaling 7% CO(2)-93% O(2). Chaos was identified through noise titration (noise limit, NL) and the sensitivity to initial conditions was assessed through the largest Lyapunov exponent (LLE). Breath-by-breath variability was evaluated using the coefficient of variation of several ventilatory variables. Chaos was consistently present in ventilatory flow recordings, but mechanical loading did not alter NL, LLE, or variability. In contrast, CO(2) altered chaos and reduced variability. In conclusion, inspiratory loading - and any resultant respiratory-related cortical activity - were not associated with changes in ventilatory chaos in this study, arguing against suprapontine contributions to ventilatory complexity.