Biological zero of laser Doppler fluxmetry: microcirculatory correlates in the hamster cheek pouch during flow and no flow conditions.

The microcirculation of the hamster cheek pouch was visualized by the intravenous injection of FITC-dextran 150,000 during normal flow conditions and when flow was interrupted by clamping proximal to the pouch. Laser Doppler fluxmetry (LDF) was used to evaluate flow during control, 30 min of occlusion and after reperfusion. Intravital video recordings of the microcirculation during occlusion show that blood moves between the different arteriolar segments after occlusion and during the whole period of no flow. This motion was oscillatory in nature, had maximum velocity of order of 30 microns sec-1, and was related to progressive decrease of arteriolar diameter. The LDF output was in the range of 60-100 AU during control. This value fell in the range of 5-25 +/- 15% AU during occlusion and was assumed to constitute the biological zero for this system. The variability of the LDF signals was characterized by the autoregressive modeling power spectrum technique. The power spectra during control, occlusion, and reperfusion were similar, suggesting that motion of blood not related to perfusion or blood flow is present in all conditions. These findings suggest that the biological zero arises from signals that are not flow related and that it should be subtracted from the flow signal.