Defining abnormal flow-mediated slowing of brachial–radial pulse wave velocity, a noninvasive vasoreactivity test

Objectives: Flow-mediated slowing (FMS) reflects macrovascular reactivity by quantifying the decline in brachial–radial pulse wave velocity (PWV) during reactive hyperaemia. We identified abnormal FMS response using normal values and integrative algorithms. Methods: In this cross-sectional, observational study, 408 community-dwelling individuals underwent FMS testing with 5 min of upper arm occlusion. FMS was assessed at 30 s intervals for 4 min postocclusion. From 76 healthy individuals, we extracted limits of normality for peak FMS, defining an abnormal peak response if PWV slowed by less than 9.4% (if <60 years) or 4.6% (if ≥60 years). Group-based trajectory modelling (GBTM) assigned participants to distinct FMS response groups. Multivariable regression identified clinical correlates of the FMS response groups. Results: Higher age correlated independently with less decline in PWV in the early phase ( P ≤ 0.0076 for 0–30 s), whereas higher SBP and no beta blocker use were linked to less decline overall (SBP: P ≤ 0.048 for 0–210 s; beta blockers: P ≤ 0.014 for 0–180 s). Abnormal peak FMS was associated with higher SBP [adjusted odds ratio (OR): 1.31, P = 0.0017) and less use of beta blockers (adjusted OR: 0.44, P = 0.041). A three-group GBTM model identified a low, moderate and high FMS response group. The risk for a low FMS response increased with age, SBP and no use of beta blockers ( P ≤ 0.038 for all). Conclusion: Abnormal FMS response was linked to cardiovascular risk factors such as ageing, hypertension and beta blocker use. The FMS response patterns may enable qualitative interpretation of FMS tests, though validation against hard clinical outcomes is warranted.