REPRODUCIBILITY OF THE CIRCADIAN SYSTOLIC BLOOD-PRESSURE VARIATION INTHE ELDERLY

Objectives: To establish the reproducibility of the nocturnal systolic blood pressure (SEP) change in elderly subjects and to examine the us e of cumulative sums (cusums) analysis in the assessment of circadian SEP variation. Subjects: Forty-two untreated elderly subjects (35 hype rtensive, 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 fr om 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 reprodu cible, with a coefficient of variation > 130%. A substantial proportio n 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 variat ion) with coefficients of variation falling to 40 and 38%, respectivel y. Conclusions: The use of fixed time definitions results in poor repr oducibility of the circadian SEP change in the elderly, which will lea d to regression dilution bias when studying the relationship of circad ian SEP variation to outcome measures in hypertension. The notion of d ipping and non-dipping circadian blood pressure patterns should be aba ndoned in favour of more reproducible cusums-based measures of circadi an blood pressure variation.