9.9 FLOW-MEDIATED SLOWING AS A NOVEL METHOD FOR THE NON-INVASIVE ASSESSMENT OF ENDOTHELIAL FUNCTION

Abstract

Background: Flow-mediated slowing (FMS) assesses the slowing of pulse wave velocity (PWV) in response to reactive hyperaemia, to provide a measure of endothelial function. We assessed the reproducibility of FMS and whether the technique is sensitive to the influence of age. FMS was compared to the commonly used, but technically demanding, alternative measure of endothelial function, flow-mediated dilatation (FMD). Methods: PWV was measured using the Vicorder device, with cuffs placed around the upper arm and wrist. FMD was assessed in the contralateral arm. The reproducibility of FMS was assessed in 23 subjects on two separate occasions. FMS and FMD were also assessed concurrently in 23 younger subjects (mean age 22±2years, 11 males) and 13 older subjects (mean age 69±6years, 7 males), all of whom were normotensive and not taking vasoactive medication. Response to glyceryl trinitrate (GTN, 25 μg administered sublingually) was also assessed with both techniques. Results: FMS was reproducible, with positive correlations between repeat visits (r =0.56, P=0.003). FMS and FMD did not correlate (r=0.23, P=0.18) whereas GTN mediated responses did (rho=0.42, P=0.01). Comparisons between younger and older groups demonstrated that FMS, FMD and GTN-mediated slowing were all significantly attenuated in older subjects (P<0.01 for all) but there was no age-related difference in GTN-mediated dilatation (p=0.7). Conclusions: FMS is a reproducible technique that is sensitive to the influence of age, but does not correlate with FMD. The extent to which FMS represents endothelial function is worthy of further investigation.