Problems Involved in the Measurement of Microcirculation by Means of Microelectrodes

Abstract

Until now, the interpretation of local wash-out curves, measured by means of microelectrodes and using hydrogen as diffusible indicator, is an unsettled problem. It has been shown, that even the simultaneous measurement by means of a surface-multiwire-Pt-microelectrode at the isolated and hemoglobin-free perfused rat liver yields different wash-out curves (4). These differences occur with regard to the height of the curves as well as to the moment, when the maximum of the indicator’s concentration is seen by the microelectrode. Fig.1 represents four simultaneously recorded curves. The difference in sensitivity of each micro-electrode has been compensated by a computer. The fast curve corresponds the real input function to the liver and is directly measured in the inflow by means of a non-compensated electrode. Usually the evaluation of local hydrogen wash-out curves is performed in the same way as the evaluation of those clearance curves, which are measured by a large-scale detector, using 85-Krypton or 133-Xenon as indicator. The most commonly used methods are the slope-method (2) and the heightover-area-method (5). Application of these methods to local hydrogen wash-out curves yields different values for the local perfusion rate. Fig.2 shows the comparison between the mean perfusion rates, determined by means of the total inflow, and the local perfusion rates. In fig.2A the local perfusion rates were calculated using the height-over-area-method, whereas in fig.2B the slope-method was applied to the same curves.