Thermography as potential real-time technique to assess changes in flow distribution in hemofiltration

Flow distributions are critical determinants in the function of hemofilters. Despite their importance, however, flow distributions cannot currently be measured in filters during experimental or clinical applications. Here, we demonstrate that the thermal conduction properties of extracorporeal circuits may provide a tool to overcome this limitation. More specifically, we show that thermography provides an indirect approach to visualize differences in regional perfusion rates through temperature profiles on the filter surface. Thermograms were recorded using a TVS700 system (Ca. Goratec) during recirculating in vitro hemofiltration of porcine blood. Different test protocols were executed to characterize the contribution of thermal conduction and convection to the measurable changes in the temperature at the surface of the filter housing. For comparison and validation, these experiments were supplemented by computer tomography (CT) of filters after dye injection. Thermography enabled real-time visualization of the flow distributions in a hemofilter. Moreover, 'point' trends taken from different regions of the filter provided quantitative information about changes of flow distributions in response to changing experimental conditions. Our preliminary data suggest that thermography is a promising new approach for assessing the principles and time-related changes in flow distributions in hemofiltration. As expected, resolution is lower than that in CT measurements and further studies will be necessary to determine the smallest temperature gradient that still identifies differences in regional perfusion rates. Given its potential to develop into an inexpensive tool for the 'bedside' level monitoring of flow distributions during clinical studies, further investigation of thermography is highly desirable.