A method to define reference profiles for ambulatory blood pressure, with application to blood pressure profiles in 158 young subjects.

Ambulatory blood pressures (systolic, SBP, diastolic, DBP) and heart rate were determined over 24 h every 15 min in the day and every 15 min in the night in 72 normal subjects aged 21 +/- 1 SEM with normal casual office pressures (WHO's criteria: office DBP less than or equal to 90 mmHg, office SBP less than or equal to 140 mmHg) and in 86 essential hypertensive subjects aged 21 +/- 1, with borderline office pressure (WHO's criteria: office DBP less than or equal to 95 mmHg, office SBP less than or equal to 160 mmHg). Complete 24-hour profiles (mean +/- SD) were reported. In the average, mean ambulatory DBP in the normal group was about 72.5 mmHg in "day time" (9 a.m.-9 p.m.) and 63.5 mmHg in "night time" (midnight-7 a.m.). Ambulatory SBP in the normal group were about 126 mmHg and 110 mmHg for the same time periods. In the borderline hypertensive group, the figures were 74 mmHg (day-time) and 67 mmHg (night time) for diastolic pressure and 140 mmHg (day time) and 118 mmHg (night time) for systolic pressure. However, when the normal and borderline groups were defined as above on the basis of office pressure, ambulatory blood pressure profiles in the two groups showed a large overlap. A method was proposed to reduce this overlap by partially reallocating the subjects on the basis of ambulatory blood pressure. First, a typical profile was defined for each group and a distance was defined between two arbitrary profiles. Then a subject in the normal (resp. hypertensive) group was reallocated to the hypertensive (normal) group if his profile was closer to the typical profile of the hypertensive (normal) group than the typical profile of his own group. Applied to ambulatory DBP profiles, this method reallocated 49 subjects (over the total of 158), significantly reduced the initial overlap of BP profiles between the two groups, and defined reference profiles for "normal" and "borderline" ambulatory blood pressures.