Changes in blood pressure and systemic vascular resistance do not predict microvascular structure during treatment of mild essential hypertension

Background: Essential hypertension is characterized by small artery remodeling and increased systemic vascular resistance (SVR). We hypothesized that changes in SVR index (SVRI) were associated with measures of small artery structure as reflected by minimum coronary and forearm vascular resistance (C-Rmin and F-Rmin, respectively). Also, we investigated how F-Rmin is related to C-Rmin, coronary flow reserve (CFR), left ventricular mass index (LVMI) and blood pressure (BP). Method: Sixty-six never-treated patients with uncomplicated mild essential hypertension had the following measured at baseline: 24-h blood BP, LVMI, CFR and C-Rmin (echocardiography), F-Rmin (forearm plethysmography) and SVRI determined by a gas re-breathing method. After 6 months of antihypertensive therapy administered by the general practitioner, the patients returned for follow-up measurements. Results: Changes in SVRI did not correlate to changes in F-Rmin (r = 0.001, P = 0.98) or C-Rmin (r = 0.13, P = 0.39) but did correlate to changes in CFR (r = 0.30, P = 0.04). Further analysis was performed by assigning the patients into two groups according to the median of drop in F-Rmin. When adjusted in a multivariate model, changes in F-Rmin (−8.1 ± 3.2%) were significantly associated with changes in C-Rmin (−9.3 ± 4.9%) and LVMI (−6.9 ± 1.7%) (P < 0.01), but not to either 24-h BP, SVRI or CFR. Conclusion: The results show that changes in neither BP nor SVRI reflected changes in minimum vascular resistance. However, changes in the forearm and coronary microcirculation occurred in parallel. Moreover, we demonstrated that neither BP nor SVRI reduction can predict changes in microvascular structure in hypertension. Thus, direct measurements of microvascular structure are needed to determine whether improvement is obtained.