METHODOLOGICAL ASPECTS OF THE EVALUATION OF ENDOTHELIUM-DEPENDENT VASODILATATION IN THE HUMAN FOREARM

The present study, involving 56 healthy subjects from a health screeni ng, was undertaken to address some methodological questions regarding the measurement of endothelial function using local intra-arterial inf usions of metacholine (2 and 5 mu g min(-1)) to evaluate endothelium-d ependent vasodilatation, and sodium nitroprusside (SNP, 5 and 10 mu g min(-1)) to evaluate endothelium-independent vasodilatation. Forearm b lood flow (FBF) was measured by venous occlusion plethysmography. The ratio of FBF during the highest dose of metacholine to FBF during the highest dose of SNP was used as an index of endothelial function. In 1 0 young volunteers the procedure was repeated after 2 h and again afte r 3 weeks in order to study short-term and long-term reproducibility o f the method. Neither the vasodilatatory response to metacholine (r = 0.006) nor that to SNP (r = 0.08) was related to resting FBF. Neither the circumference nor :che length of the arm was related to endothelia l function (r = 0.01-0.11), as evaluated by the FBF on metacholine to nitroprusside ratio (mean 1.3 +/- 0.3 SD). The use of a wrist cuff to exclude hand circulation, or not, did not influence the evaluation of endothelial function significantly. Maximal FBF after 3 min of arteria l occlusion of the forearm was significantly related to blood flow dur ing both metacholine (r = 0.53, P < 0.01) and nitroprusside Infusion ( r = 0.36, P<0.05), but not to the FBF on metacholine to nitroprusside ratio (r = 0.01). The short-term and long-term reproducibility of FBF during vasodilatation with metacholine and SNP was good (r = 0.89-0.97 , P<0.001), while the individual measurements for resting FBF were les s reproducible when repeated after 3 weeks (r = 0.34). In conclusion, endothelial function was not related to resting FBF, nor to the arm ci rcumference or length, No major difference was seen whether endothelia l function was evaluated with or without exclusion of the hand circula tion. Maximal FBF during reactive hyperaemia was not related to endoth elial function.