Transcapillary diffusion of Na-fluorescein measured by a 'large window technique' in skin areas of the forefoot.

A method is introduced for the study of transcapillary diffusion of 20% Na-fluorescein (0.3 ml/l of blood given intravenously) in skin areas by a fluorescence video-microscopy system which has been used earlier for measurements at the single capillary level or on axes crossing capillary groups. Two groups of 17 and 14 healthy volunteers respectively were included in a test-retest experiment (first measurement at day one, second measurement at day three). The appearance of the dye was visualized and the intensity of fluorescent light measured by a quadratic video densitometer window at the forefoot in an area of 2 mm2 containing 78 capillaries on the average. In both groups with and without control of the skin temperature, there were no statistically significant differences of the mean values measured at the first and second day of study. However, the mean intraindividual differences and the coefficients of variance were significantly (p less than 0.005) higher in the subjects without temperature control. It is concluded that the method is suited to detect transcapillary diffusion of Nafluorescein in skin areas by an almost atraumatic procedure with acceptable reproducibility. Potentially, it may be used to follow the natural history of microvascular diseases and to test the effect of various treatment modalities.