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Twenty-four hour ambulatory blood pressure in the population
F Nyström1, O Malmström, B E Karlberg
1Department of Endocrinology, Faculty of Health Sciences, University Hospital, Linköping, Sweden.
Objectives:
To establish a population-based 24-h ambulatory blood pressure (ABP) reference material with day/night mean BP calculated by standardized and true bedtimes.
Design:
A cross-sectional study of 200 randomly selected subjects (20 men and 20 women in each 10-year age interval 20-70 years) in Linköping, Sweden.
Setting:
University Hospital of Linköping, Sweden.
Results:
Participation rate was 67%. Mean supine clinic BP (CBP) and 24-h-ABP values for the whole material were 123 +/- 13/79 +/- 8 mmHg and 120 +/- 10/73 +/- 7 mmHg, respectively. White coat BP phenomenon increased with age (systolic CBP/ABP ratio versus age, r = 0.35, P < 0.0001). Seventeen participants had a night/day mean arterial blood pressure ratio > 0.9 (non-dipper) when calculated from their own time-notations. If standardized day (06.00-23.00) and night (23.00-06.00) limits were used, 24 subjects were non-dippers. Of these, only eight were 'true'. 'True' non-dippers had a similar day-time mean arterial ABP as 'true' dippers (92.4 +/- 11 mmHg versus 91.9 +/- 13 mmHg, P = 0.92) while night-time BP was higher (89.9 +/- 13 mmHg versus 74.1 +/- 7 mmHg, P < 0.0001).
Conclusion:
Population-based ABP reference values have been defined. We found 9% non-dippers and that standardized day/night-time limits may lead to misclassification. This could be due to gender- and age-differences in sleeping habits, which was also shown in this study. The frequency of white coat BP phenomenon increases with age.