Patients with renal dysfunction have longer time to nighttime blood pressure dip, researchers report

Patients with renal dysfunction may experience a delay in the time it takes before their blood pressure (BP) falls during the night, according to findings from a recent study. "Because glomerular filtration capability is one of the major factors determining sodium sensitivity, as a function of loss of glomerular filtration rate, the nocturnal dip in BP may be less pronounced," the authors of the study wrote. To determine whether the dipping time--defined as the duration before mean...

Patients with renal dysfunction may experience a delay in the time it takes before their blood pressure (BP) falls during the night, according to findings from a recent study.

"Because glomerular filtration capability is one of the major factors determining sodium sensitivity, as a function of loss of glomerular filtration rate, the nocturnal dip in BP may be less pronounced," the authors of the study wrote.

To determine whether the dipping time--defined as the duration before mean arterial pressure falls to <90% of daytime average--is longer with worse renal functioning, researchers examined ambulatory BP measurements and urinary sodium excretion rates during day and night to estimate circadian rhythms in 65 patients with chronic kidney disease (CKD) who were hospitalized at Japan's Nagoya City University Hospital.

Results indicated that nocturnal decline in mean arterial pressure was significantly less pronounced with worse renal functioning (represented as a significant interaction by 2-way analysis of variables [ANOVA]; P<.0001). Specifically, when patients were stratified by creatinine clearance, the night/day ratio of mean arterial pressure was significantly higher among patients in the third tertile (5-41 mL/minute) than in the first tertile (91-164 mL/min; P<.0001), and this ratio was significantly inversely correlated with creatinine clearance (P<.0001).

The nocturnal decline in urinary sodium excretion rates was also less pronounced with worse renal functioning (2-way ANOVA; P<.0001), the authors noted. Although patients' 24-hour urinary sodium excretion rate did not differ significantly across tertiles (P=.07), as renal function worsened, the daytime urinary sodium excretion rate was significantly reduced (P<.0001) in the third tertile versus the first tertile, while the nighttime rate showed a trend toward an increase (P=.08).

Additionally, the night/day ratio of urinary sodium excretion rates was significantly higher in the third tertile than in the first tertile (P<.0001) and was significantly inversely correlated with creatinine clearance (P<.0001). As renal function deteriorated from the first to third tertiles, urinary sodium concentration was significantly lowered during both daytime (P=.001) and nighttime (P=.01).

Dipping times differed significantly across tertiles (P<.0001) and were significantly longer in the third tertile than in the first tertile (P<.0001). Dipping times were inversely correlated with creatinine clearance (P<.0001) but were positively correlated with the night-to-day ratios of mean arterial pressure (P<.0001) and urinary sodium excretion rates (P<.0001). These patterns remained even after excluding 24 patients who did not experience nocturnal dipping.

Finally, when cumulative incidence rates of the nocturnal dip were compared across tertiles of renal function, nocturnal dip was significantly more common in the first tertile than in the third tertile (P<.0001), and only creatinine clearance significantly predicted nocturnal BP dip (HR, 1.017; 95% CI, 1.008-1.026; P=.0002) in multivariate analysis. Compared with the first tertile, patients in the third tertile were 80% less likely to experience nocturnal BP dip (HR, 0.20; 95% CI, 0.08-0.55; P=.002).

"Because it is well known that BP during sleep has a greater impact on cardiovascular disease than BP during daytime, circadian BP rhythm itself must be considered as one of the important risk factors for cardiovascular disease," the authors concluded. "Dipping time may be used as a novel marker to quantitatively analyze circadian BP rhythm. Furthermore, shortening dipping time may become a new target of antihypertensive therapy in future."

These findings were published online Oct. 20 ahead of print by the journal Hypertension by Fukuda M, et al.