Impact of venous return on pulmonary oxygen uptake kinetics during dynamic exercise: in silico time series analyses from muscles to lungs

摘要

The aim of the present study was to investigate whether a single-compartment (SCM) and a multi-compartment (MCM) venous return model will produce significantly different time-delaying and distortive effects on pulmonary oxygen uptake ((V) over barO(2pulm)) responses with equal cardiac outputs ((Q)over dot) and muscle oxygen uptake ((V) over barO(2musc)) inputs. For each model, 64 data sets were simulated with alternating Q. and (V) over barO(2musc) kinetics-time constants (tau) ranging from 10 to 80 s-as responses to pseudorandom binary sequence work rate (WR) changes. Kinetic analyses were performed by using cross-correlation functions (CCFs) between WR with (V) over barO(2pulm) and (V) over barO(2musc). Higher maxima of the CCF courses indicate faster system responses-equal to smaller tau values of the variables of interest (e. g., tau(V) over barO(2musc)). The models demonstrated a highly significant relationship for the resulting (V) over barO(2pulm) responses (r 0.976, P 0.001, n 64). Both models showed significant differences between(V)over barO-2pulm and (V) over barO(2musc) kinetics for (V) over barO(2musc) ranging from 10 to 30 s (P 0.05 each). In addition, a significant difference in (V)over barO-2pulm kinetics (P 0.05) between the models was observed for very fast (V)over barO-2musc kinetics (tau 10 s). The combinations of fast ((Q)over dot dynamics and slow (V) over barO(2musc) kinetics yield distinct deviations in the resultant (V) over barO(2pulm) responses compared with (V) over barO(2musc) kinetics. Therefore, the venous return models should be used with care and caution if the aim is to infer (V) over barO(2musc) by means of (V) over barO(2pulm) kinetics. Finally, the resultant (V) over barO(2pulm) responses seem to be complex and most likely unpredictable if no cardiodynamic measurements are available in vivo.