Determining the Repeatability of Low Flow Mediated Constriction and Total Vessel Reactivity in the Brachial Artery of Humans

Abstract

Endothelial function is the ability of an artery to vasodilate and can be assessed using a flow mediated dilation (FMD) test. While FMD is a useful tool for assessing endothelial function, it has been argued that it does not capture overall vascular function. Two novel measures, low flow mediated constriction (L-FMC) and total vessel reactivity (TVR) have been introduced to compensate for the potential limitations of FMD. Unfortunately, little is known about the repeatability of brachial artery L-FMC and TVR. Additionally, it is unclear how L-FMC and TVR might be influenced by age, sex and the presence of cardiovascular disease (CVD) or CVD risk. Therefore, the main purpose of this investigation was to assess the day-to-day repeatability of FMD, L-FMC and TVR in the brachial artery. The secondary purpose was to assess if FMD, L-FMC and TVR were associated with age and if this relationship was influenced by sex or the presence of CVD or CVD risk factors. 375 participants (age:37±22) were included in the study, 98 participants (age:34±19) underwent two FMD tests and were included in the repeatability analysis. For all participants brachial artery endothelial function was assessed using a FMD test. The day-to-day repeatability of FMD was substantial (ICC=0.68), L-FMC was slight (ICC=0.01) and TVR was moderate (ICC=0.50). Age was associated with FMD and TVR (ρ=-0.24, ρ=-0.19, p<0.005), however there was no relationship between age and L-FMC. The relationships between age and FMD and TVR persisted in individuals with CVD and CVD risk factors, and sex did not moderate the relationship between age and any of our vascular outcomes. These results indicate that brachial artery FMD and TVR are relatively repeatable, however L-FMC is not repeatable. As well, it appears that age is associated with a decrease in FMD and TVR, but not related to L-FMC.