Reactivity to low‐flow as a potential determinant for brachial artery flow‐mediated vasodilatation

Previous studies have reported a vasoconstrictor response in the radial artery during a cuff‐induced low‐flow condition, but a similar low‐flow condition in the brachial artery results in nonuniform reactivity. This variable reactivity to low‐flow influences the subsequent flow‐mediated dilatation (FMD) response following cuff‐release. However, it is uncertain whether reactivity to low‐flow is important in data interpretation in clinical populations and older adults. This study aimed to determine the influence of reactivity to low‐flow on the magnitude of brachial artery FMD response in middle‐aged and older individuals with diverse cardiovascular risk profiles. Data were analyzed from 165 individuals, divided into increased cardiovascular risk (CVR: n = 115, 85M, 67.0 ± 8.8 years) and healthy control (CTRL: n = 50, 30M, 63.2 ± 7.2 years) groups. Brachial artery diameter and blood velocity data obtained from Doppler ultrasound were used to calculate FMD, reactivity to low‐flow and estimated shear rate (SR) using semiautomated edge‐detection software. There was a significant association between reactivity to low‐flow and FMD in overall (r = 0.261), CTRL (r = 0.410) and CVR (r = 0.189, all P < 0.05) groups. Multivariate regression analysis found that reactivity to low‐flow, peak SR, and baseline diameter independently contributed to FMD along with sex, the presence of diabetes, and smoking (total R (2) = 0.450). There was a significant association between reactivity to low‐flow and the subsequent FMD response in the overall dataset, and reactivity to low‐flow independently contributed to FMD. These findings suggest that reactivity to low‐flow plays a key role in the subsequent brachial artery FMD response and is important in the interpretation of FMD data.