Repeated clinic blood pressure measurement was compared with non-invasive ambulatory blood pressure (ABP) monitoring in 10 elderly subjects with isolated systolic hypertension (ISH) and 11 normotensive controls (NT). 2. Subjects were assessed on four occasions at weekly intervals. None was receiving antihypertensive or vasoactive medication. 3. Mean clinic blood pressure was consistently higher than mean daytime ABP in both clinical groups. This effect was greater for systolic (SBP) than diastolic blood pressure (DBP) and in the ISH group compared with the NT group. The reproducibility of the clinic minus ABP difference was high in both groups; the mean +/- s.d. of the differences was 26 +/- 15/9 +/- 2 mmHg in the ISH group and 7 +/- 18/8 +/- 9 mmHg in the controls. 4. ABP readings were normally distributed for both SBP and DBP in both groups. In the ISH group, the frequency distribution of SBP readings was shifted to the right whilst the distribution of DBP readings overlapped that of the NT subjects. 5. These results suggest a pressor response may largely account for the elevated SBP seen in elderly subjects with sustained ISH based on casual readings.
