Differences between daytime and nighttime blood pressure variability regarding systemic atherosclerotic change and renal function

Abstract

Recently, new parameters related to hypertension, such as variability in blood pressure and ambulatory arterial stiffness index (AASI), were demonstrated to correlate with arteriosclerotic change. In this study, we investigated the correlation between circadian variability in blood pressure/AASI and renal function. We also investigated differences in the clinical impact of 24 h, daytime and nighttime blood pressure variability on renal and systemic atherosclerotic changes. We analyzed data from 120 patients who underwent renal Doppler ultrasonography (RDU) and ambulatory blood pressure monitoring (ABPM) at our hospital ward, and investigated the correlation between circadian variability in blood pressure/AASI and renal function, including resistive index (RI) evaluated with RDU, which is thought to be a good indicator of renal vascular resistance. Subjects with higher circadian variability in systolic blood pressure (SBP) had significantly higher RI. Daytime variability in SBP correlated more strongly with RI than nighttime variability. Meanwhile, only nighttime variability, but not daytime variability, in SBP was related to carotid atherosclerosis. Similarly, AASI was significantly correlated with RI. Circadian variability in SBP and AASI were both significantly correlated with renal function. Daytime SBP s.d. was especially more strongly correlated with renal vascular resistance, and nighttime SBP s.d. was significantly correlated with intima-media thickness (IMT) and plaque score. These results indicate that evaluating both daytime and nighttime blood pressure variability enables an assessment of pathological conditions in hypertensive patients to prevent cardiovascular diseases.