Reliability of nocturnal blood pressure dipping.

BACKGROUND: Increasing evidence documents the fact that individuals whose blood pressure drops or 'dips' relatively little at night have a higher risk of numerous cardiovascular illnesses. OBJECTIVE: To examine the reliability of various measures of nocturnal blood pressure dipping. METHODS: This study examined 17 individuals with ambulatory blood pressure monitoring on three 24 h recordings while they pursued a schedule similar to that of in-patients on a clinical research unit. Nocturnal dipping of blood pressure was scored three ways: as the drop in blood pressure between 10 p.m. and 6 a.m. ('clocktime'), as the drop in blood pressure tailored to each individual's reported bedtime ('bedtime'), and as the drop in blood pressure accompanying polysomnographically verified sleep ('sleeptime'). RESULTS: Adequate reliability was obtained for all three measures of dipping. There was, in general, a significant correlation across testing occasions (P<0.05). The correlation coefficient ranged from 0.5 to 0.8, depending on which criterion of dipping was selected and whether the endpoint was systolic blood pressure, diastolic blood pressure, or mean arterial blood pressure. CONCLUSIONS: The reliability of systolic blood pressure dipping was somewhat lower than that of diastolic or mean arterial blood pressure dipping. Dipping appears to be a reliable construct. While no one definition of dipping was demonstrably better than another, the most sensible definition of dipping would allow some adjustment for defining 'night' on the basis of each individual's idiosyncratic bed time.

Effect of continuous positive airway pressure on blood pressure : a placebo trial.

This study examined the effect of continuous positive airway pressure (CPAP) treatment on blood pressure in patients with obstructive sleep apnea. Thirty-nine patients with sleep apnea were studied. Ambulatory blood pressure monitoring was obtained before and after patients were randomized to receive either 1 week of CPAP or placebo CPAP (CPAP administered at ineffective pressure). Blood pressure was examined over daytime hours (6 AM to 10 PM) and during nighttime hours (10 PM to 6 AM). Daytime mean arterial blood pressure decreased significantly but equally in both the active treatment group and the placebo treatment group (P=0.001). Nighttime mean arterial pressure levels decreased to a much greater extent over time in the patients who received active CPAP treatment (P=0. 032). CPAP does appear to decrease nighttime blood pressure. However, the decrease in daytime blood pressure may reflect a nonspecific response (ie, placebo), since both the active treatment group and the placebo treatment group developed comparable decreases in blood pressure.

Race and diurnal blood pressure patterns. A review and meta-analysis.

Investigators have reported variable findings regarding the role of race in diurnal blood pressure patterns. We performed a review and meta-analysis of this literature to identify the overall effect of race on circadian blood pressure patterns. Eighteen studies involving 2852 participants were reviewed. Meta-analyses were conducted using effect sizes calculated from the data provided directly in the study reports. Separate meta-analyses were conducted on effect sizes for differences between blacks and whites in daytime and nighttime systolic and diastolic blood pressure and nocturnal dip in systolic and diastolic blood pressure. To evaluate discrepancies in findings from studies involving American versus non-American blacks, overall meta-analyses as well as within-subset meta-analyses of black/white differences were conducted for comparisons involving American and non-American blacks. Results of overall meta-analyses indicate that blacks experience higher levels of systolic and diastolic blood pressure, both at night and during the day. These differences were significantly greater at night than during the day (P<0.05). Results of within-subset analyses involving American blacks mirrored those for all black/white comparisons, except that the effect of race on nocturnal dip, ie, that American blacks experienced less of a dip in both systolic and diastolic blood pressure at night, was significant (P<0.05). In contrast, the effect of race on nocturnal dip was not significant for comparisons involving non-American blacks. These results suggest a consistent difference in the chronobiology of blood pressure, particularly in American blacks.