Patterns of diffusion through skin capillaries in patients with long-term diabetes

We used intravital fluorescence videomicroscopy to study the pattern of transcapillary and interstitial diffusion in the nail folds of 13 patients with long-term diabetes and of 12 healthy controls. In both groups intravenously injected sodium fluorescein left the intravascular compartment. Its distribution in the pericapillary space and in the remote parts of the interstitial space was measured on single frames of the television tape by videodensitometers that are sensitive to intensities of fluorescent light. In the diabetics the dye passed both physiologic diffusion barriers--the capillary wall and the pericapillary space--in significantly increased amounts (P less than 0.01). The enhanced penetration of the tracer into the remote area caused an early homogeneous, milky blurring of the capillary image, whereas in the controls the pericapillary space remained clearly delineated for as long as 40 to 50 minutes after the appearance of the dye. The altered pattern of diffusion could be explained by increased permeability of the diffusion barriers, or, alternatively, by either changes of the mobility of the dye due to binding of the dye by intravascular or interstitial proteins or abnormal hemodynamics in the microvascular circulation. This technique provides a quantitative, noninvasive method of studying the natural history of diabetic microangiopathy.