Heterogeneity of laser Doppler flowmetry in perfused muscle indicative of nutritive and nonnutritive flow

Laser Doppler flowmetry (LDF) signal responses have been compared with metabolic changes using both a surface macroprobe and randomly placed implantable microprobes in muscles of the constant-flow-perfused rat hindlimb. Changes in response to total flow and to vasoconstrictors that are known to increase (norepinephrine, NE) or decrease (serotonin, 5-HT) hindlimb oxygen uptake were assessed. The surface macroprobe (anterior end of biceps femoris) identified only one type of LDF response characterized by increased signal in response to NE and decreased signal in response to 5-HT. Implanted microprobes (tibialis, gastrocnemius, vastus, or biceps femoris) identified sites that gave three LDF responses of differing character. These responses were where the LDF signal increased with NE and decreased with 5-HT (56.7%), where the LDF signal decreased with NE and increased with 5-HT (16.5%), or where there was no net response to either vasoconstrictor (24.7%). The data are consistent with discrete regions of nutritive and nonnutritive flow in muscle where flow in each as controlled by vasoconstrictors relates directly to the metabolic behavior of the tissue.