Usefulness of the resistive index in renal Doppler ultrasonography as an indicator of vascular damage in patients with risks of atherosclerosis.

Background. Chronic kidney disease (CKD) is caused by various risk factors of cardiovascular disease (CVD). The estimated glomerular filtration rate (eGFR) is commonly used for the evaluation of the renal function in patients with CKD; however, it is difficult to assess the pathogenesis of CKD and predict the renal prognosis accurately using only eGFR. The resistive index (RI) in renal Doppler ultrasonography (RDU) is thought to be a good indicator of renal vascular resistance caused by atherosclerosis. In the present study, we investigated whether RI could be used to evaluate the pathogenesis of renal damage and predict the renal prognosis and investigated the correlation between RI and blood pressure (BP) fluctuations in patients with or without hypertension. Methods. The total study population included 194 patients (mean age: 66.2 years), who underwent RDU in our hospital ward between February 2009 and July 2010. We investigated the correlation between RI and multiple clinical parameters, including ambulatory blood pressure monitoring (ABPM). Results. RI significantly correlated with age, eGFR, diastolic BP, pulse pressure and level of albuminuria. Patients with diabetes mellitus (DM) showed a significantly higher RI than patients without DM, although their eGFR was similar; thus, DM might accelerate renal vascular damage and RI could detect earlier changes of vascular damage proceeding the time eGFR is reduced. Regarding ABPM, patients with a larger morning surge [systolic blood pressure (SBP) in the early morning-lowest SBP during sleep] showed a significantly higher RI. Conclusions. The present study indicated that RI might be very useful for the evaluation of very early renal damage more effectively than eGFR and that diurnal BP change might be partly due to the progression of atherosclerotic change in the kidney evaluated by RI.