Kinetics analysis of muscle arterial-venous O(2) difference profile during exercise.

Muscle vascular dysfunction, a hallmark of chronic diseases such as heart failure and diabetes, impairs the matching of blood flow (Q(m)) to O(2) utilization (V(O(2m))) following exercise onset. One recently described consequence of this behavior is that arterial-venous O(2) difference [(a-v)(O(2)), the mirror image of muscle vascular oxygenation] transiently overshoots the subsequent steady-state and, in so doing, may provide important information regarding Q(m) versus V(O(2m)) dynamics. Using computer simulations, we tested the hypothesis that key parameters of the (a-v)(O(2)) overshoot - peak response, downward time constant (tau(D)), and total area - would relate quantitatively to Q(m) kinetics. Our results demonstrated significant proportionality (all p<0.01) between Q(m) mean response time and peak (r(2)=0.56), tau(D) (r(2)=72) and total area (r(2)=0.97) of (a-v)(O(2)) overshoot. These results suggest that analysis of (a-v)(O(2)) or its proxy, muscle vascular oxygenation [measured using near-infrared spectroscopy or phosphorescence quenching], provides valuable information regarding blood flow and vascular function particularly in reference to V(O(2m)) kinetics.