Marked increases in systemic blood flow in resistant or refractory hypertensives of African ancestry in Africa.

AIMS: A distinct volume-dependent increase in systemic blood flow has recently been demonstrated to contribute to hypertension in groups of African ancestry. We determined whether systemic blood flow contributes to resistant or refractory hypertension (RHTN).

METHODS

We compared the multivariate adjusted haemodynamic correlates of blood pressure in RHTN ( n  = 100) on diuretic and other therapy, to those in age and sex-matched normotensives (NT, n  = 128), untreated hypertensives (Untreat-HTN, n  = 124), and treated-controlled hypertensives (Control-HTN, n  = 74) of African ancestry in South Africa. Haemodynamics were determined from velocity and diameter measurements in the left ventricular outflow tract, and central arterial pressures.

RESULTS

All hypertensives had higher stroke volume (SV), cardiac output (CO) and peak aortic flow (Q) compared to NT ( P  < 0.05 to <0.0001). However, RHTN had higher SV, CO and Q than Untreat-HTN and Control-HTN ( P  < 0.0001). Proximal aortic characteristic impedance (Zc) in RHTN was similar to Untreat-HTN, but greater than NT ( P  < 0.005), and Control-HTN ( P  < 0.05). In RHTN, systemic vascular resistance was lower compared NT, Untreat-HTN and Control-HTN ( P  < 0.005 to <0.0001), and total arterial compliance was higher compared to Untreat-HTN and Control-HTN ( P  < 0.02 to <0.0001). The pressure generated by the product of Q and Zc (P QxZc ) and hence aortic pulse pressure were higher in RHTN compared to NT, Untreat-HTN and Control-HTN ( P  < 0.0001), effects attributed primarily to increases in SV and Q.

CONCLUSIONS

Despite the use of diuretic therapy, increases in systemic blood flow are the main determinant of RHTN in groups of African ancestry in South Africa. Novel approaches to targeting volume-dependent increases in blood flow in this population are therefore required.