Repeated automatic versus ambulatory blood pressure measurement: the effects of age and sex in a normal ageing population.

Objectives: To study blood pressure adaptation in relation to age and sex. In a subsample, laboratory blood pressure measurements were compared with ambulatory daytime blood pressure measurements to determine the degree of agreement between the two methods. The night-time blood pressure reduction was analysed as a function of blood pressure status, age and sex.

Design: A cross-sectional study in 469 healthy volunteers, aged 23-82 years, stratified for age, sex and educational level.

Methods: Laboratory blood pressure was measured automatically (Dinamap 8100) five times during a 20 min recording session. Cardiovascular events in the medical history were identified in order to treat the cardiovascular event-free group separately in subsequent analyses. Within 3 weeks after laboratory blood pressure measurement, ambulatory blood pressure was measured for 24 h in 135 volunteers from the main study.

Results: Both diastolic and systolic blood pressure varied markedly in a single measurement session as a function of age, independent of mean pressure level. After 15 min no further blood pressure decrease was observed. On the basis of the average of the final two blood pressure measurements, 18.8% of the subjects were in the hypertensive range (WHO/ISH guidelines). Ambulatory blood pressure measurements were in accord with earlier findings and correlated 0.74 and 0.73 with laboratory diastolic and systolic blood pressure, respectively, but weighted kappa values indicated only moderate agreement (0.42 and 0.51). Women showed a more profound reduction in cnight-time blood pressure than did men.

Conclusions: There is a substantial change in blood pressure during a single measurement session which is greater in older age groups. The moderate agreement between the two methods of blood pressure measurement supports the notion that blood pressure measured in a single session has limited generalizability to average daytime levels in a population sample.