Renal resistive index in patients with true resistant hypertension: results from the RESIST-POL study

Background: Increased ultrasound Doppler renal resistive index (RRI) is a marker of atherosclerotic and hypertensive organ damage both at renal and systemic level. Aim: To evaluate RRI in patients with true resistant hypertension (TRHT) in the RESIST-POL study. Methods: From 204 patients diagnosed with TRHT in the RESIST-POL study, 151 patients (90 male, 61 female, mean age: 47.7 +/- 10.4, range: 19-65 years) without secondary hypertension were included into the analysis. All patients were characterised by estimated glomerular filtration rate > 60 mL/min/1.73 m(2) and no history of diabetes prior to the study. As a control group we included 50 age-and gender-matched patients (35 male, 15 female, mean age: 46.8 +/- 10.4, range: 19-65 years) with primary well-controlled hypertension. The groups also did not differ in respect to the number of years of known history of hypertension. The RRIs were evaluated on the basis of the Doppler ultrasound examination. Increased RRI was defined as >= 0.7. Results: Both groups did not differ in terms of renal function. Patients with TRHT were characterised by higher RRI as compared with the group with well-controlled hypertension (0.62 +/- 0.05 vs. 0.60 +/- 0.05, p < 0.05). In the TRHT group RRI correlated significantly with age, clinic and ambulatory blood pressure measurement, diastolic blood pressure (DBP) levels, as well as with clinic pulse pressure (PP) (r = 0.297; p = 0.001), with daytime (r = 0.355; p < 0.001) and nighttime (r = 0.313; p < 0.001) PP, and with fasting glucose concentration (r = 0.215; p = 0.008) and E/E' ratio (r = 0.289; p = 0.001) on echocardiography. RRI values were significantly higher in TRHT patients with newly diagnosed diabetes as compared with TRHT patients without diabetes (0.65 +/- 0.05 vs. 0.62 +/- 0.05, p = 0.022). Age, daytime DBP, daytime PP, and E/E' ratio but not fasting glucose concentration correlated independently with RRI in the model. Among patients with TRHT, patients with increased RRI were characterised by older age (52.2 +/- 4.9 vs. 47.3 +/- 10.6 years, p = 0.012), higher body mass index (32.8 +/- 6.0 vs. 29.7 +/- 4.5 kg/m(2), p = 0.034), as well as lower daytime and nighttime DBP values and lower daytime and nighttime heart rate, as compared to patients with RRI < 0.7. The TRHT patients with increased RRI as compared to patients with RRI < 0.7 were characterised also by higher daytime and nighttime PP. Both groups did not differ in respect of renal function. Conclusions: Our study showed that the patients with TRHT were characterised by significantly higher RRI values as compared to the subjects with well-controlled hypertension. It may also be suggested that in the subjects with TRHT renal vascular resistance is related to blood pressure values, selected echocardiographic abnormalities, and some surrogate markers for metabolic and cardiovascular events, including fasting glucose plasma concentration and PP, respectively.