Purpose: There are no data in the literature to our knowledge related to changes in renal resistive index (RRI) values over 24-h period and the importance of detecting these changes in patients who have hypertension (HT). In this study, we aimed to investigate the variation of RRI values over 24-h period and its usability in hypertensive patients.
Methods: A total of 118 subjects (80 with HT and 38 healthy controls) were included in the study. Morning, midday, evening, and midnight RRI, renal pulsatility index, and accelerated time were measured by Doppler ultrasonography (US). B-mode US and elastograpic assessment were performed only in the morning.
Results: Temporal RRI varied significantly (p < 0.001). The highest and lowest levels were found in the morning and evening, respectively. All temporal RRI levels were significantly higher in patients with HT (both p < 0.001). The absolute and relative increases in RRI (ΔRRI) levels were similar in two groups. All temporal RRI measurements positively correlated with the patient age, pulse pressure, renal cortical thickness, and cortical stiffness. However, absolute-ΔRRI and relative-ΔRRI positively correlated with the age. Absolute-ΔRRI positively correlated with the pulse pressure and cortical stiffness, and no correlation was observed between relative-ΔRRI and these variables. Of the four temporal measurements, morning RRI were found to be independently associated with cortical stiffness (p < 0.001).
Conclusions: RRI measurements varied over 24-h period in patients with HT and/or healthy controls. Morning RRI was significantly higher than other day time, and it is also related to renal cortical stiffness.
Keywords: Hypertension; Renal resistive index; Variation.