PATHOPHYSIOLOGY OF HYPERTENSION

Abstract

Objective: The Xenon-133 washout technique can be used to assess mean renal blood flow as well as intrarenal blood flow patterns. Disappearance of tracer from the kidney generally follows either a bi-exponential or a mono-exponential decay pattern. The latter pattern suggest homogenization of blood flow. In addition, oscillatory patterns in the decay curves may point to local vasomotor activity. In this study, we compared patients with essential hypertension (EH) to patients with hypertension due to fibromuscular dysplasia (FMD) or atherosclerotic renal artery stenosis (ARAS) to assess possible differences in Xenon washout characteristics between these groups. Design and method: Renal blood flow was measured by injecting Xenon-133 gas through a catheter placed in the renal artery and monitoring the disappearance of the isotope within 180 seconds. The acquired curves were fitted to one- or two-phase decay models and oscillation in the curves was calculated using standard deviation of residuals. All measurements were obtained before contrast was injected. Results: There were no differences in the number of one-phase or two-phase fits between groups (p = 0.135). For two-phase decays, the fast component was markedly lower in both FMD and ARAS groups compared to EH (p < 0.001). The slow component was lower in ARAS compared to EH (p = 0.002). Mono-exponential decay values did not differ significantly between groups (p = 0.088). Oscillations in curves were lesser in EH as compared to both FMD (p = 0.004) and ARAS (p < 0.001). Conclusions: A fall in the fast blood flow component in FMD and ARAS may be due to either redistribution of blood flow from cortical nephrons with a high perfusion rate to deeper nephrons with slower flow rates or to possible recruitment of ‘dormant’ cortical nephrons. Differences between ARAS and FMD groups in fast and slow flow could mean that the responsible pathophysiological process has proceeded further in ARAS compared to FMD. Enhanced oscillation patterns may be due to an increase in local vasomotor activity. Lesser oscillation in EH patients could mean that this pathophysiological process is not activated in this group.