However, the complexity of the underlying mechanism of the reaction to the iontophoresis of Ach makes its use as a specific test of endothelial function debatable . Moreover, other limitations must be acknowledged, including non-specific effects, and poor reproducibility when LDF is used . Therefore, studies using iontophoresis must be carefully designed to reduce these, and LDI rather than LDF is recommended to assess perfusion. Provided that a low intensity current is used (i.e., <100 μA), saline
should be preferred as the control (Figure 3). Pre-treatment with a local anesthetic is a way to limit axon reflex-induced vasodilation . Limiting current density (<0.01 mA/cm2) and charge density (<7.8 mC/cm2) also ACP-196 decreases current-induced vasodilation . Finally, skin resistance may be reported and can be readily approximated by connecting a
voltmeter in parallel . Perfusion data may then be normalized to skin resistance, or resistance can be standardized by adjusting the distance between the electrodes. PORH refers to the increase in skin blood flow above baseline levels following release from brief arterial occlusion . Many mediators contribute to PORH. Sensory nerves are partially involved through an axon reflex response [84,88]. Local mediators include large-conductance calcium activated potassium (BKCa) channels that seem INCB018424 supplier to play a major role , suggesting that EDHF is involved, whereas results are conflicting concerning Dehydratase the implication of prostaglandins [8,29,95]. The
inhibition of NO synthesis does not alter PORH on the forearm , but recent work suggests that COX inhibition unmasks the NO dependence of reactive hyperemia in human cutaneous circulation . On the finger pad, however, the response seems to be partly NO-dependent . In summary, PORH should not be considered as a test for microvascular endothelial function itself, but could be used as a tool to detect overall changes in microvascular function. Various parameters can be quantified from the flux response after arterial occlusion (Figure 4). One of the most commonly used is peak hyperemia, whether expressed as a raw value or as a function of baseline, i.e., area under the curve, peak minus baseline or relative change between peak and baseline expressed as a percentage, calculated from [(peak − baseline)/baseline] × 100. Peak perfusion may also be scaled to the so-called maximum vasodilation achieved when the skin is heated to 42°C or higher . Time to peak perfusion is another parameter quantified when performing PORH, but its physiological significance as a marker of skin microvascular reactivity remains to be established. When assessed with single-point LDF, the inter-day reproducibility of PORH is variable, depending both on the skin site, the way of expressing data, and the baseline skin temperature (Table 1).