Evidence of flowmotion induced changes in local tissue oxygenation

The effect of cyclic blood flow velocity on local tissue oxygenation was studied by means of a mathematical simulation in the situation where red blood cells (RBC) act as discrete oxygen sources. Cyclic time varying fluctuations of capillary blood (flowmotion) are due to arteriolar vasomotion. This effect was introduced into the model as an oscillating RBC velocity with equal periods of high and low velocity regulated by a square wave function. Changes in RBC velocity coupled with a constant time-average capillary hematocrit lead to periods of high and low flux. Input parameters were flowmotion frequency and amplitude, capillary hematocrit, and mean RBC velocity. All results were related to baseline states where the velocity and hematocrit are steady. Our principle finding is that flowmotion alters the tissue oxygenation, whereby: 1) high amplitudes of flowmotion cause a modest increase in axial delivery of oxygen but with a decreased average tissue pO2; 2) decreasing flowmotion frequencies lead to increased radial penetration of oxygen; 3) the lower frequencies of flowmotion cause an increase in the volume of tissue that achieves at least a pO2 level of 5 mmHg. Isovolemic hemodilution was simulated and found to substantially increase the volume of oxygenated tissue as a function of flowmotion. These findings indicate that pO2 transients caused by flowmotion oxygenate tissue domains which under steady-state conditions would remain anoxic.