Muscle blood flow-O2 uptake interaction and their relation to on-exercise dynamics of O2 exchange

A computer model was developed to provide a theoretical framework for interpreting the dynamics of muscle capillary O2 exchange in health and disease. We examined the effects of different muscle oxygen uptake (V˙O2m) and CvO2 profiles on muscle blood flow (Q˙m) kinetics (Q˙m=V˙O2m/[CaO2−CvO2]). Further, we simulated V˙O2m and Q˙m responses to predict the CvO2 profile and the underlying dynamics of capillary O2 exchange (CvO2=CaO2−V˙O2m/Q˙m). Exponential equations describing V˙O2m, CvO2 and Q˙m responses in vivo were used in the simulations. The results indicated that Q˙m kinetics were relatively insensitive to CvO2 parameters, but directly associated with V˙O2m kinetics. The biphasic Q˙m response produced a substantial fall in CvO2 within the first 15-20 s of the exercise transition (phase 1 of Q˙m). These results revealed that the main determinant of CvO2 (or O2 extraction) kinetics was the dynamic interaction of Q˙m and V˙O2m kinetics during phase 1 of Q˙m.