Evaluation of four different methods to measure endothelium-dependent vasodilation in the human peripheral circulation

At present, several techniques exist that claim to evaluate endothelium-dependent vasodilation (EDV) in the human peripheral circulation. The present study aims to evaluate the relationships between four of these techniques. A group of 24 young, healthy subjects underwent measurements of EDV and endothelium-independent vasodilation (EIDV) in predominately resistance vessels in the forearm using the invasive forearm technique with local infusion of methacholine and sodium nitroprusside, evaluation of flow-mediated vasodilation (FMD) in the conduit brachial artery measured by ultrasound, with or without the addition of ischaemic hand exercise, and evaluation of the reduction in the relative height of the inflection point of the radial pulse wave following β₂-adrenergic receptor stimulation. The reduction in the relative height of the inflection point following β₂-adrenergic receptor stimulation was significantly related to both EDV and EIDV in the forearm (r =-0.41 and r =-0.42 respectively; both P<0.05), but not to the EDV/EIDV ratio (r =-0.10). However, FMD, with or without the addition of ischaemic hand exercise, was not significantly related to the results obtained using the other two techniques (r =-0.18 to +0.13). In conclusion, the reduction in the relative height of the inflection point of the pulse wave following β₂-adrenergic receptor stimulation was related to both EDV and EIDV measured by the invasive forearm technique, indicating that the pulse wave technique does not measure EDV specifically. FMD in the brachial artery, with or without ischaemic hand exercise, was not significantly related to values obtained using the other two techniques, indicating that endothelial function differs between conduit and resistance arteries, and that both of these measurements should be evaluated in future studies.