Fluorescein flowmetry: a method for measuring relative capillary blood flow in the intestine

The present work represents an attempt to develop a method for measuring relative blood flow in intestinal capillaries, by the use of sodium fluorescein (Na-F) as an indicator substance. The method is called fluorescein flowmetry (FF). A mathematical model was developed; blood flow was expressed as an index between the maximum fluorescence obtained during the first circulatory passage of Na-F and the rise time, defined as the time interval between 10 and 90% of the maximum fluorescence. The prerequisites for the mathematical model were tested in experiments in animals and man. The extraction of Na-F in the intestinal capillaries was found to be more than 99%. The ratio between the tissue clearance and uptake was found to be 0.0051, indicating no back flux. Experiments in man revealed that the rise time was proportional to the mean transit time and the mean transversal time of the bolus proper. The accuracy of FF was confirmed in man where the ratio between mucosal and serosal-muscular capillary blood flow was 2:1. From the results obtained, it appears that FF can be used as a method for measuring relative capillary blood flow in the intestine.