Nocturnal blood pressure dipping in the hypertension of autonomic failure

Abstract

Blood pressure (BP) normally decreases during the night. Absence of this phenomenon (nondipping) is associated with increased cardiovascular risk. Altered autonomic and endocrine circadian rhythms are suspected to play a role. Patients with peripheral autonomic failure offer a unique opportunity to study this phenomenon, because approximately 50% develop supine hypertension despite very low autonomic function. The purpose of this study was to define the prevalence of dipping in these patients and to determine whether dipping is associated with less severe autonomic impairment or exaggerated nocturnal sodium excretion. We collected BP and urine from 8:00 pm to 8:00 am in 41 peripheral autonomic failure patients with supine hypertension. Dipping (systolic BP fall >or=10% during 12 am to 6 am from baseline [8 pm to 10 pm]) occurred in 34% of patients, with an average decrease of -44+/-4 mm Hg at 4 am. Systolic BP, averaged from 12 am to 6 am, decreased to normotensive levels in 50% (n=7) of dippers and 15% (n=7) of nondippers. There were no significant differences in the severity of autonomic failure, nocturnal diuresis, or natriuresis (0.18+/-0.01 in dippers versus 0.18+/-0.01 mEq/mg of creatinine in nondippers; P=0.522) between groups. At 8:00 am, orthostatic hypotension was similar between groups (-84/-35+/-9/4 mm Hg in dippers versus -93/-39+/-6/3 mm Hg in nondippers; P=0.356 for systolic BP). In conclusion, dipping was observed in one third of patients with peripheral autonomic failure, so that a significant percentage of patients would not require treatment for supine hypertension. Dipping was not associated with increased nocturnal urinary sodium or volume excretion or less severe autonomic failure. Thus, mechanisms independent of autonomic pathways contribute to BP dipping in these patients.

Figures

Figure 1

Nighttime systolic and diastolic blood pressure (left axis), and heart rate (right axis) averaged every two hours from 8PM to 8AM in dippers (solid lines) and non-dippers (discontinued lines). Baseline ("daytime") period was defined from 8PM to 10PM and the sleeping period ("nighttime") from 12AM to 6AM (horizontal bar). Values are expressed as means±SEM. * p

Figure 2

Floating bargraphs denote systolic and diastolic blood pressure in the supine posture (closed bars) and after one minute upright (open bars), taken at 8AM in dippers (left panel) and non-dippers (right panel). Corresponding heart rates are denoted by the closed circles.

Figure 3

Bargraphs denote urinary volume (left) and sodium excretion (right, corrected for creatinine) collected from 8PM to 8 AM in dippers and non-dippers.

Figure 4

Change in mean systolic BP (SBP) from 8PM to 4AM (maximal decrease) in non-dippers (white bars) treated with placebo or nitroglycerin (NTG), and in dippers (black bar) treated with placebo. *p=0.048 by Wilcoxon signed-rank test. **p