Normal values for ambulatory blood pressure and differences between casual blood pressure and ambulatory blood pressure

OBJECTIVE: To determine normal values for 24 h ambulatory blood pressure in a Danish population and to study the relationship to casual blood pressure. STUDY POPULATION: A random sample of 2656 Danish men and women participated in a population survey. The participants were selected in age groups and were aged 41-42, 51-52, 61-62 or 71-72 years during the survey. METHODS; Casual blood pressure (standard mercury sphygmomanometer) and 24 h ambulatory blood pressure (Takeda TM-2421) were measured successfully in 2082 subjects. All subjects under antihypertensive treatment (247) were excluded, restricting the study population to 1835 participants. RESULTS: Casual and 24 h ambulatory blood pressure were correlated (P < 0.0001) in all age and sex groups. Casual systolic/diastolic blood pressures were 129.6+/-17.8/82.6+/-10.3 for men and 125.1+/-18.2/79.7+/-9.9 mmHg for women. Twenty-four-hour average blood pressures were 130.8+/-14.2/75.3+/-8.6 for men and 122.4+/-14.9/69.6+/-8.3 mmHg for women. A multivariate linear logistic regression model confirmed that a high casual blood pressure (odds ratios 11/7 for systolic/diastolic blood pressure; P=0.001) was the major determinant of a lower ambulatory than casual blood pressure; age and sex were less important. CONCLUSION: The relationship between casual blood pressure on the one hand and the difference in casual and 24 h ambulatory blood pressure on the other hand suggests that ambulatory blood pressure represents a regression towards the mean compared to casual blood pressure. Any definition of an upper normal level of 24 h ambulatory blood pressure that is derived from a correlation between casual and ambulatory measurements will be inaccurate, and must await long-term studies of the relationship between ambulatory blood pressure and subsequent cardiovascular events.