EVALUATION OF THE DETERMINANTS OF FLOW - MEDIATED RADIAL ARTERY VASODILATATION IN HUMANS

The relative importance of the early peak response during hyperaemia a nd of the duration of the hyperaemic phase (t1/2: blood now velocity h alf time and AUCt1/2: area under the curve of flow velocity at t1/2) i n the magnitude of the flow-dependent vasodilatation of the radial art ery was determined in humans. Radial artery diameter was measured cont inuously in 18 healthy volunteers using an echo-tracking system couple d to a Doppler device for the measurement of the radial blood flow. In 9 subjects, arterial parameters were measured at baseline and during 3 hyperaemic tests performed after 2, 5 or 10 minutes of ischaemia. Re producibility of the measured parameters was studied in 9 other subjec ts. Radial artery diameter, AUCt1/2 and t1/2 increased proportionally with the duration of ischaemia. In contrast, the peak flow response wa s already maximal after 5 minutes of ischaemia. The regression analysi s showed that the best fit model after stepwise analysis only included t1/2 (r=0.85, p<0.001). There was no correlation between the peak flo w values and the duration of hyperaemia (r=0.29, p=0.14). These result s demonstrate that conduit arteries postischaemic flow-dependent vasod ilatation in humans is both determined by the peak value and by the du ration of the hyperaemic phase and suggest that these two components m ust be consirered when comparing this index of NO release between diff erent groups of subjects.