Impact of Family History of Hypertension on Racial Differences in Flow‐Mediated Dilation and Reactive Hyperemia

Abstract

The prevalence of hypertension and cardiovascular disease is highest in non-Hispanic black (BK) individuals. This has led to a number of studies investigating potential racial differences in vascular function, assessed as flow-mediated dilation (FMD, macrovascular function) and reactive hyperemia (RH, microvascular function). These studies suggest that otherwise healthy BK individuals may have reduced vasodilator responses, compared to white (WH) individuals. However, it is notable that these studies did not consider the participants' family history of hypertension (FHH), which is important because studies have shown that individuals with a positive (+) FHH exhibit blunted vasodilator function compared to those with no FHH (-FHH). Hence, whether the higher prevalence of +FHH among BK individuals contributed to the previously reported differences in FMD and RH between BK and WH individuals is unknown. Thus, we aimed to investigate the impact of FHH on FMD and RH in BK and WH males. We hypothesized that FMD and RH would be attenuated in BK compared to WH males, and further, a +FHH would reduce FMD and RH compared to a -FHH in both groups. We studied 17 young healthy BK (+FHH: n = 9) and WH males (+FHH: n = 9). Heart rate (ECG) and brachial artery diameter and blood velocity (duplex Doppler Ultrasound) were continuously measured while subjects laid supine. Baseline measures were recorded for 2 min, following which a cuff placed around the forearm was rapidly inflated to 220 mmHg for 5 min. All measurements were recorded for 30 s prior to and 3 min after cuff release. FMD was quantified as a percent change in brachial artery diameter from baseline to peak diameter after cuff release. The impact of shear rate on FMD was controlled for statistically using an ANCOVA. RH was quantified as peak blood velocity and hyperemic blood velocity area under the curve (AUC) to 60s after cuff release. Baseline brachial artery diameter and blood velocity were not different between groups (P > 0.05 for all comparisons). FMD was significantly blunted in BK (4.12 ± 0.64%, Mean ± SE) compared to WH males (6.00 ± 0.49%; P = 0.025), and remained significantly blunted after controlling for impact of shear rate on FMD (BK: 4.19 ± 0.58% vs. WH: 5.93 ± 0.58%; P = 0.046). There was no effect of FHH on FMD in either race (interaction and main effect of FHH P > 0.05). Likewise, RH was significantly blunted in BK compared to WH males when quantified as peak blood velocity (BK: 58 ± 3 cm.s-1 vs. WH: 70 ± 4 cm.s-1, P = 0.025), as well as hyperemic blood velocity AUC to 60s (BK: 1419 ± 85 a.u. vs. WH: 1738 ± 123 a.u., P = 0.041), with no effect of FHH in either race (interaction and main effect of FHH P > 0.05 for both measures). These preliminary findings suggest that young healthy BK males exhibit attenuated FMD and RH compared to their WH counterparts; an effect that appears to be independent of FHH.