Correlation between Blood Pressure Changes Assessed by 24-hour Ambulatory Blood Pressure Monitoring and Urine Microalbuminuria Excretion Rate in Normal and Essential Hypertension

To document the correlation between renal damage and circadian blood pressure variation, urinary microalbumin excretion rate (UAER) and 24-hour ambulatory blood pressure monitoring (24-hr ABPM) were performed in 16 normotensives and 29 stage I–III essential hypertensive subjects (whole-day mean BP; 120.13/79.06 mmHg vs 152.59/94.31 mmHg, p<0.05). The BP variables of 24-hr ABPM included hourly mean arterial pressure (MAP), maximum, minimum and mean systolic and diastolic BP of the awaking (daytime) and sleep time (nighttime), and whole-day mean BP. Subsequently, BP reduction of maximum, minimum and mean BP between awaking time and sleep time were also calculated as other variables. UAER was not different between the normotensive and hypertensive group (9.44 ± 11.48 vs 11.87 ± 9.27 μg/min, p>0.05). 10 subjects (2/16 in normal vs 8/29 subjects in hypertensives) revealed over 16 μg/min of UAER. All of the awaking BP variables and whole-day mean BP were correlated with the UAER in whole subjects and hypertensives, but almost sleep BP variables except maximum DBP and mean DBP were not. On the contrary, only daytime minimum DBP and SBP were correlated with UAER in normotensives. The common best correlated BP variable in awaking time was minimum BP (DBP and SBP; r=0.49, r=0.44 in whole, r=0.51, r=0.58 in hypertensives, r=0.54, 0.56 in normotensives, all p<0.05). Hourly MAP at 24 PM in whole subjects (r=0.49, p<0.05) and that of at 22 PM in hypertensives were best correlated (r=0.71, p<0.05). Those from 15 PM to 1 AM in whole subjects were also significantly correlated with the UAER (r=0.33∼0.44, all p<0.05). But in hypertensives, all the hourly MAPs were correlated except those of 4, 5, 6, 10, 11 AM and 14 PM. On the contrary, in normal group, the hourly MAP were not completely related to UAER throughout 24 hours (all p=NS). Among all computed day-night BP reductions, only minimum DBP was significantly correlated with the UAER (r=0.34, p=0.022). This study suggests that not only awaking BP but also day-night minimum DBP reduction are highly responsible for the renal impairment in essential hypertension.