Functional microcirculatory impairment: A possible source of reduced skin oxygen tension in human diabetes mellitus

Lower extremity transcutaneous oxygen tension (TcPO2) is used as a diagnostic and prognostic indicator of tissue perfusion and is reduced in diabetes mellitus. Since cardiac output, leg blood flow and microvascular perfusion each can singly or jointly effect tissue oxygenation, the relative importance of macro- vs microvascular factors has not been resolved. To clarify this issue we compared TcPO2 levels in diabetic and nondiabetic subjects in whom cardiac output, leg pulsatile blood flow, and microcirculatory perfusion parameters were noninvasively measured. In 60 diabetic and 60 nondiabetic subjects the following measurements were done on both legs during a single session evaluation: foot dorsum TcPO2 at 45°, skin microvascular perfusion reserve (MVR) in response to local thermal provocation from 35 to 45° using laser-Doppler, ankle-brachial index using Doppler ultrasound (ABI), and pulsatile leg blood flow using magnetic resonance flowmetry; cardiac output was determined using transthoracic bioimpedance. The diabetic and nondiabetic groups were determined to have nonsignificant differences (mean ± SEM, DM vs NODM) with respect to age (63.3 ± 1.1 vs 60.1 ± 1.5 years), cardiac output (5.5 ± 0.2 vs 5.5 ± 0.2 l/min), leg blood flow (1.6 ± 0.05 vs 1.7 ± 0.06 ml/min/100 cc) and ABI. Although macrocirculatory values were equivalent, microvascular function indicators were significantly reduced in the diabetic group: TcPO2 (51.9 ± 1.4 vs 62.9 ± 1.3 mmHg); MVR (76.7 ± 1.5 vs 84.9 ± 0.9%) and were correlated only in diabetics (r² = 0.48, P < 0.001). The findings suggest a primary linkage between the diabetic TcPO2 deficit and the microcirculatory submaximal vasodilatory response, with little if any role of macrocirculatory factors.