Distinct Contribution of Systemic Blood Flow to Hypertension in an African Population Across the Adult Lifespan

Abstract

Although hypertension in groups of African ancestry is volume-dependent, the relative impact of systemic flow (stroke volume, peak aortic flow [Q]) versus vascular mechanisms (systemic vascular resistance, aortic characteristic impedance [Zc], total arterial compliance) components of arterial load has not been evaluated across the adult age range. In participants of African ancestry (n=824, age=16–99 years, 68.3% female), using central arterial pressure and aortic velocity and diameter measurements in the outflow tract, we determined the hemodynamic correlates of age-related increases in blood pressure. Strong independent positive relations between age and stroke volume or peak aortic Q were noted ( P <0.0001), effects associated with ventricular end diastolic volume and aldosterone-to-renin ratios. Age-related increases in mean arterial pressure were associated with stroke volume and not systemic vascular resistance. Although age-Q relations began from early adulthood, initially an inverse association between age and aortic Zc ( P <0.0001) driven by increments in aortic root diameter ( P <0.0001) prevented an enhanced systolic blood pressure and pulse pressure. When Zc began to positively relate to age ( P <0.0001), age-Q relations translated into increases in forward wave pressures and hence systolic blood pressure and pulse pressure. Age relations with pulse pressure were as strongly determined by Q as by Zc or total arterial compliance (0.027±0.001 versus 0.028±0.001 and 0.032±0.003 mm Hg per yearly increase in pulse pressure produced by Q, Zc, and total arterial compliance; P <0.0001). Uncontrolled hypertension (confirmed with 24-hour blood pressure) was determined more by Q, Zc, and total arterial compliance than by increases in systemic vascular resistance ( P <0.0005 for comparison). In conclusion, relationships between age and systemic blood flow contribute markedly to hypertension in groups of African origins.

Marked intrafamilial aggregation and heritability of aortic flow in a community with prevalent volume-dependent hypertension in Africa

“…In this regard, more women than men volunteered for the present study and hence the present findings may relate more to women than to men. However, the contribution of Q to age-related increases in BP and the correlates of Q in the present population are similar in women and men [6]. Thus, it is likely that the genetic factors that determine Q have similar effects in both sexes.…”

“…In this regard, variations in brachial PP are largely determined by the pressure generated by the product of aortic Q and Z c . Furthermore, the impact of systemic flow on BP is far greater than that of systemic vascular resistance (SVR) [6]. Thus, in contrast, to several populations around the world, in groups of African ancestry living in Africa, increases in systemic flow are as important as the vascular determinants of BP in the pathogenesis of hypertension [6,7].…”

“…Furthermore, the impact of systemic flow on BP is far greater than that of systemic vascular resistance (SVR) [6]. Thus, in contrast, to several populations around the world, in groups of African ancestry living in Africa, increases in systemic flow are as important as the vascular determinants of BP in the pathogenesis of hypertension [6,7]. Although renal mechanisms explain the marked increases in systemic flow but not alternative haemodynamic determinants of BP [8], current antihypertensive therapy, including diuretic therapy has no proven ability to produce sustained decreases in systemic blood flow.…”

“…However, the extent to which increases in systemic flow as compared with vascular mechanisms responsible for increases in BP are inherited in African populations is unknown. As the impact of increases in systemic flow in Africa is on hypertension associated with increases in SBP rather than on isolated increases in DBP [7], in the present study, we therefore, aimed to compare the intrafamilial aggregation and heritability of peak aortic flow (Q) to that of aortic characteristic impedance to flow (Z c ), and total arterial compliance (TAC), the dominant vascular factors that determine PP and hence SBP in Africa [6,7].…”

Increased Backward Wave Pressures Rather than Flow Explain Age-Dependent Heart Rate Effects on Central, But not Peripheral Arterial Pressure

“…In the present study performed in a community sample studied across the full adult age range, we therefore performed central arterial waveform analysis from both flow and pressure assessments (Figure S1). 13,[17][18][19] Making use of the range of physiological resting HR values that occur in any population, we thereby determined the mechanisms responsible for the associations between HR and Pf and hence PPc and the impact of age thereon.…”