Periwound skin microcirculation of venous leg ulcers

Chronic venous ulceration has an estimated prevalence of from 0.06 to 1.3% with about 57 to 80% of patients with leg ulcers having demonstrable venous disease. The sequence of events whereby chronic venous insufficiency leads to leg skin ulceration is not yet worked out. Venous hypertension may set the stage for subsequent ulcer development via linkages to observed changes in skin microvessel metrics, morphology, rheology, permeability, hemodynamics, and the interstitium. Periulcer measurements show decreased transcutaneous oxygen and elevated carbon dioxide tensions, yet the skin blood perfusion measured with laser Doppler fluxometry (LDF) is reported to be elevated. This elevated perfusion, (Q), could be due to independent changes in blood velocity (U), and volume (V), with different mechanistic implications depending on the mode. Thus, we sought to determine the relative contributions of these two components with the aim of clarifying the mechanism responsible for the reported skin flow changes. Patients studied (n = 16) had unilateral venous ulcers, an ankle/brachial BP index >0.8, and venous pathology demonstrated by duplex imaging. Ulcer areas ranged from 0.6 to 76.9 cm² (mean = 13.7 cm²) and were present for 2 to 144 months, mean = 32. With the patient supine, Q (ml/min/100 g), V (%), and U (mm/sec) were measured by LDF (Vasamedics, BPM403A) at two to three sites on periulcer skin and compared with measurements at corresponding sites on the nonulcerated limb at local skin temperatures of 35 and 44. Results confirm an elevation in basal periulcer flow (7.0 vs 1.8 ml/min/100 g, P = 0.001) and show this to be due to elevations in both circulating blood volume (1.24 vs 0.62%, P < 0.001) and velocity (1.23 vs 0.65 mm/sec, P =.004). Maximal Q, V, and U were also higher on the ulcer leg, being for Q, 11.2 vs 6.42 ml/min/100 g, P = 0.03; for V, 1.49 vs 1.13%, P =.002; and for U, 1.76 vs 1.33 mm/sec, P = 0.020. Expressing each leg's basal values as a percentage of its own maximal response shows the ulcerated leg to have higher values for Q, V, and U, with (ulcer leg/control leg) ratios being 2.5, 1.8, and 1.4, respectively. These findings show that the LDF perfusion increase is due to roughly equal increases in microvessel circulating blood volume and velocity. Based on the present functional data and the preponderance of in vivo microvessel changes reported in the literature, a plausible and consistent characterization of the periulcer tissue is one of a tissue in which the number of microvessels is reduced, with the remaining ones carrying a greater blood volume at an increased blood velocity.