Factors Critical to Iontophoretic Assessment of Vascular Reactivity: Implications for Clinical Studies of Endothelial Dysfunction

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Abstract
Skin microvascular responses to iontophoresis of acetylcholine, an endothelium-dependent vasodilator, and sodium nitroprusside, an endothelium-independent vasodilator, were measured using a laser Doppler imager whose software controlled iontophoretic current delivery in an integrated fashion. A novel feature involved monitoring voltage across the iontophoresis chambers during current application (total charge: 8 mC). Both drugs elicited vasodilatation but with differing magnitudes and time courses, whereas current delivery with only vehicle (0.5% NaCl) present was ineffective. During drug delivery a three-to fourfold difference in calculated skin resistance was observed between subjects, with higher resistance being associated with lower dilator responses to both drugs. There was a significant (p r