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 O(2) exchange in health and disease. We examined the effects of different muscle oxygen uptake (V O(2m)) and CvO(2) profiles on muscle blood flow (Q (m)) kinetics (Q (m)=V O(2m)/[CaO(2)-CvO(2)]). Further, we simulated V O(2m) and Q (m) responses to predict the CvO(2) profile and the underlying dynamics of capillary O(2) exchange (CvO(2)=CaO(2)-V O(2m)/Q (m)). Exponential equations describing V O(2m), CvO(2) and Q (m) responses in vivo were used in the simulations. The results indicated that Q (m) kinetics were relatively insensitive to CvO(2) parameters, but directly associated with V O(2m) kinetics. The biphasic Q (m) response produced a substantial fall in CvO(2) within the first 15-20s of the exercise transition (phase 1 of Q (m)). These results revealed that the main determinant of CvO(2) (or O(2) extraction) kinetics was the dynamic interaction of Q (m) and V O(2m) kinetics during phase 1 of Q (m).