ArticlesPrognostic accuracy of day versus night ambulatory blood pressure: a cohort study
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.
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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)
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José Boggia and Yan Li contributed equally to this manuscript
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IDACO investigators listed at end of article