Laser Doppler flowmetry during hyperaemic reactions in the skin.

Laser Doppler flowmetry (LDF) was used to study skin blood flow in the finger tip and on the dorsum of the hand in healthy volunteers. Vasodilatation in the finger tip was induced by immersing the arm in water at 42 degrees C, and vasodilatation in the dorsum of the hand by intracutaneous injection of dihydralazine. Simultaneous measurements were performed using venous occlusion plethysmography (finger tip) and 133Xe clearance (dorsum of hand). Three output signals from the laser Doppler flowmeter were recorded. The LDFPf-1 value is linearly related to the blood flow, provided the concentration of blood cells in the scattering volume is low. The LDFPf-2 value is generated by a signal processor designed to give linearity even at higher concentrations of moving blood cells (CMBC), the latter quantity being reflected by the CMBC value. During vasodilatation by immersion, all laser Doppler values from the finger tip increased but less than the total finger blood flow as measured using venous occlusion plethysmography. Intracutaneous injection of dihydralazine in the dorsum of the hand caused markedly increased CMBC values and the increase in LDFPf-2 was significantly greater than that of LDFPf-1. The increase in 133Xe clearance was less pronounced. The results indicate that capillary blood flow as well as blood flow in vessels below the capillary level contribute to the Doppler signal. However, flow through the arteriovenous shunts in the finger tip seems to be only partially registered by the laser Doppler technique. The higher the CMBC value, the more obvious is the difference between LDFPf-1 and LDFPf-2 values. When using laser Doppler flowmetry, the addition of CMBC value registration may be helpful in clarifying changes in microvascular blood flow.