Elsevier

The Lancet

Volume 370, Issue 9594, 6–12 October 2007, Pages 1219-1229
The Lancet

Articles
Prognostic accuracy of day versus night ambulatory blood pressure: a cohort study

https://doi.org/10.1016/S0140-6736(07)61538-4Get rights and content

Summary

Background

Few studies have formally compared the predictive value of the blood pressure at night over and beyond the daytime value. We investigated the prognostic significance of the ambulatory blood pressure during night and day and of the night-to-day blood pressure ratio.

Methods

We did 24-h blood pressure monitoring in 7458 people (mean age 56·8 years [SD 13·9]) enrolled in prospective population studies in Denmark, Belgium, Japan, Sweden, Uruguay, and China. We calculated multivariate-adjusted hazard ratios for daytime and night-time blood pressure and the systolic night-to-day ratio, while adjusting for cohort and cardiovascular risk factors.

Findings

Median follow-up was 9·6 years (5th to 95th percentile 2·5–13·7). Adjusted for daytime blood pressure, night-time blood pressure predicted total (n=983; p<0·0001), cardiovascular (n=387; p<0·01), and non-cardiovascular (n=560; p<0·001) mortality. Conversely, adjusted for night-time blood pressure, daytime blood pressure predicted only non-cardiovascular mortality (p<0·05), with lower blood pressure levels being associated with increased risk. Both daytime and night-time blood pressure consistently predicted all cardiovascular events (n=943; p<0·05) and stroke (n=420; p<0·01). Adjusted for night-time blood pressure, daytime blood pressure lost prognostic significance only for cardiac events (n=525; p≥0·07). Adjusted for the 24-h blood pressure, night-to-day ratio predicted mortality, but not fatal combined with non-fatal events. Antihypertensive drug treatment removed the significant association between cardiovascular events and the daytime blood pressure. Participants with systolic night-to-day ratio value of 1 or more were older, at higher risk of death, and died at an older age than those whose night-to-day ratio was normal (≥0·80 to <0·90).

Interpretation

In contrast to commonly held views, daytime blood pressure adjusted for night-time blood pressure predicts fatal combined with non-fatal cardiovascular events, except in treated patients, in whom antihypertensive drugs might reduce blood pressure during the day, but not at night. The increased mortality in patients with higher night-time than daytime blood pressure probably indicates reverse causality. Our findings support recording the ambulatory blood pressure during the whole day.

Introduction

In 1988, O'Brien and colleagues1 reported for the first time that an abnormal circadian blood-pressure profile with a less marked decrease in night-time blood pressure led to an increased risk of stroke. Subsequent studies of populations2, 3, 4, 5 and hypertensive cohorts6, 7, 8, 9, 10, 11, 12 generally corroborated that a raised nocturnal blood pressure predicted a higher rate of cardiovascular complications. Despite the apparent agreement between these previously published large-scale studies,2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 several potential limitations need further clarification of the prognostic accuracy of day versus night ambulatory blood pressure. Many studies considered only fatal outcomes2, 3, 10, 11 or did not have the power to study cause-specific cardiovascular endpoints.2, 3, 5, 9 Investigators dichotomised the night-to-day blood pressure ratio, and applied different definitions of dipping status or different daytime and night-time intervals. Few reports formally compared the predictive value of the blood pressure at night over and beyond the daytime value. Finally, in cohorts of patients with hypertension, antihypertensive drug treatment attenuated the association between outcome and blood pressure.7

An international consortium constructed a database of prospective population studies with the goal to advance research on the prognostic accuracy of the ambulatory blood pressure.13, 14 We aimed to report risk estimates that were independently associated with the daytime and night-time blood pressures. Additionally, we investigated in categorical and continuous analyses whether the night-to-day blood pressure ratio contained any prognostic information over and beyond the 24-h blood pressure.

Section snippets

Study population

We constructed the International Database on Ambulatory blood pressure monitoring in relation to Cardiovascular Outcomes (IDACO).13, 14 Studies were eligible for inclusion if they included a random population sample, if information about the conventional and ambulatory blood pressures and cardiovascular risk factors were available at baseline, and if the subsequent follow-up included fatal and non-fatal outcomes. We did an electronic search of studies written in English, using the search terms

Results

The study population consisted of 4358 (58%) people from Europe, 1666 (22%) from Asia, and 1434 (19%) from South America. 3416 (46%) of the participants were women, and 3436 (46%) had hypertension on conventional blood pressure measurement, 1637 (48%) of whom were taking drugs to lower their blood pressure. Mean age was 56·8 (SD 13·9) years. The mean conventional blood pressure was 132·4 (20·8) mm Hg systolic and 80·1 (11·6) mm Hg diastolic. For the 24-h blood pressure, these values were 124·8

Discussion

Our study has shown that the predictive accuracy of the daytime and night-time blood pressures and the night-to-day blood pressure ratio depended on the outcome under study. For fatal endpoints, the night-time blood pressure did better than the daytime blood pressure, and the night-to-day ratio predicted total, cardiovascular, and non-cardiovascular mortality. In contrast, for fatal combined with non-fatal outcomes, the daytime blood pressure did equally well as the night-time blood pressure,

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  • Cited by (0)

    José Boggia and Yan Li contributed equally to this manuscript

    IDACO investigators listed at end of article

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