Microvascular flow distribution and transcapillary diffusion at the forefoot in patients with peripheral ischemia

Transcapillary diffusion of Na-fluorescein injected by the intravenous route was measured by a videomicroscopy system in the skin of the dorsum of the forefoot in healthy controls (n = 21) and in patients with moderate (n = 35) and severe (n = 29) ischemia secondary to lower extremity arterial occlusive disease. Systolic ankle blood pressure and transcutaneous PO2 at the forefoot were significantly decreased in both groups of patients according to the severity of ischemic disease (p less than 0.001). The difference of the mean filling times between the first and last capillaries was used as a parameter for inhomogenous microvascular perfusion. It was significantly increased in moderate and severe ischemia (p less than 0.05). Transcapillary diffusion measured with a large window densitometer in a skin area of 2.8 mm2 was significantly enhanced in both groups of patients. The increase was more pronounced in the patients with severe ischemia (p less than 0.001) than in those with moderate ischemia (p less than 0.05). Among the patients with severe ischemia the diabetics exhibited significantly higher mean values of pericapillary fluorescence light intensity than the non-diabetics (p less than 0.001). At high magnification (550 times) distinct sites of increased transcapillary diffusion were detected in both groups of patients. They were most often localized at the apex of the capillary loops ("candle light phenomenon") and were more frequent in patients with severe than with moderate ischemia. In conclusion microvascular blood flow distribution is inhomogeneous and transcapillary diffusion increases at the level of single capillaries and skin areas in patients with moderate and especially severe foot ischemia.