REPRODUCIBILITY OF THE CIRCADIAN SYSTOLIC BLOOD-PRESSURE VARIATION IN THE ELDERLY

Objectives: To establish the reproducibility of the nocturnal systolic blood pressure (SEP) change in elderly subjects and to examine the use of cumulative sums (cusums) analysis in the assessment of circadian SEP variation. Subjects: Forty-two untreated elderly subjects (35 hypertensive, 7 normotensive) of mean age 75.5 years from the hypertension clinic at a large teaching hospital participated in a reproducibility study. Methods: Twenty-four-hour ambulatory blood pressure monitoring was performed and repeated at a median interval of 2 months (range 2 weeks to 9 months). Outcome measures: Reproducibility of circadian SEP variation from fixed time analysis of day-night SEP difference and from cusums-based parameters. Results: Twenty-four-hour SEP values were highly reproducible with a coefficient of variation of 5.8%. However, the day-night SEP difference for fixed time periods was poorly reproducible, with a coefficient of variation > 130%. A substantial proportion of subjects (36-43%) altered their 'dipping status' between visits. The use of cusums analysis improved the reproducibility of measures of circadian SEP change (cusums plot height and maximum circadian variation) with coefficients of variation falling to 40 and 38%, respectively. Conclusions: The use of fixed time definitions results in poor reproducibility of the circadian SEP change in the elderly, which will lead to regression dilution bias when studying the relationship of circadian SEP variation to outcome measures in hypertension. The notion of dipping and non-dipping circadian blood pressure patterns should be abandoned in favour of more reproducible cusums-based measures of circadian blood pressure variation.