Background: In certain patients in routine practice, blood pressure (BP) measurements differ substantially from week to week or month to month. Although often assumed to be random, such variability could provide information on underlying pathology or prognosis. In order to be informative, however, visit-to-visit BP variability would have to be neither random (i.e. it should be reproducible over time within individuals) nor artefactual (i.e. it should not be an artefact of the method/timing of measurement, for example). Methods: We quantified visit-to-visit variability in BP and explored potential confounding factors by analysing repeat measurements obtained every few months during follow-up in two large trials in patients with a transient ischaemic attack (TIA) or minor ischaemic stroke: the UK-TIA Aspirin Trial (effect of aspirin, effect of season and day of the week of measurement) and the European Carotid Surgery Trial (ECST – effect of carotid endarterectomy). By comparing different periods of follow-up, we also determined the reproducibilities of mean and several different measures of variability for both systolic (SBP) and diastolic BP (DBP). Results: The mean absolute difference between adjacent SBP readings was 14.7 mm Hg in the UK-TIA Trial and 16.0 mm Hg in ECST. Visit-to-visit variability in both SBP and DBP were independent of the potentially confounding factors studied, but reproducibility of all the variability measures was statistically significantly greater than zero. Reproducibility (intraclass correlation) of standard deviation of SBP was 0.32 (p < 0.0001) in the UK-TIA Trial and 0.18 (p = 0.0007) in ECST. Consequently, classification of patients with high (top quintile) or low (bottom quintile) variability was consistent over time (observed/expected = 2.21, 95% confidence interval 1.71–2.85, p < 0.0001, and 1.65, 1.23–2.21, p = 0.0007, respectively). Reproducibility increased with the number of measurements used to calculate variability, and was independent of any correlation with mean BP. Conclusions: Visit-to-visit variability in BP in these populations was reproducible, independently of any correlation with mean BP, demonstrating that visit-to-visit intra-individual BP variability is not random.

Keywords:
Blood pressure variability, Mean blood pressure, Reproducibility of blood pressure levels, Standard deviations in blood pressure, Stroke, Transient ischaemic attack, Variability in blood pressure measurements
1.
MacMahon S, Peto R, Cutler J, Collins R, Sorlie P, Neaton J, Abbott R, Godwin J, Dyer A, Stamler J: Blood pressure, stroke, and coronary heart disease. Part 1. Prolonged differences in blood pressure: prospective observational studies corrected for the regression dilution bias. Lancet 1990;335:765–774.
2.
Clarke R, Shipley M, Lewington S, Youngman L, Collins R, Marmot M, Peto R: Underestimation of risk associations due to regression dilution in long-term follow-up of prospective studies. Am J Epidemiol 1999;150:341–353.
3.
Lewington S, Clarke R, Qizilbash N, Peto R, Collins R: Age-specific relevance of usual blood pressure to vascular mortality: a meta-analysis of individual data for one million adults in 61 prospective studies. Lancet 2002;360:1903–1913.
4.
Wroe SJ, Sandercock P, Bamford J, Dennis M, Slattery J, Warlow C: Diurnal variation in incidence of stroke: Oxfordshire community stroke project. BMJ 1992;304:155–157.
5.
Kario K, Shimada K, Pickering TG: Clinical implication of morning blood pressure surge in hypertension. J Cardiovasc Pharmacol 2003;42(suppl 1):S87–S91.
6.
Otsuka K, Cornelissen G, Halberg F, Oehlerts G: Excessive circadian amplitude of blood pressure increases risk of ischaemic stroke and nephropathy. J Med Eng Technol 1997;21:23–30.
7.
Hossain M, Ooi WL, Lipsitz LA: Intra-individual postural blood pressure variability and stroke in elderly nursing home residents. J Clin Epidemiol 2001;54:488–494.
8.
Dawson SL, Manktelow BN, Robinson TG, Panerai RB, Potter JF: Which parameters of beat-to-beat blood pressure and variability best predict early outcome after acute ischemic stroke? Stroke 2000;31:463–468.
9.
James GD, Pickering TG, Yee LS, Harshfield GA, Riva S, Laragh JH: The reproducibility of average ambulatory, home and clinic pressures. Hypertension 1988;11:545–549.
10.
Palatini P, Mormino P, Canali C, Santonastaso M, De Venuto G, Zanata G, Pessina AC: Factors affecting ambulatory blood pressure reproducibility: results of the HARVEST trial. Hypertension 1994;23:211–216.
11.
Thomas C, Wood GC, Langer RD, Stewart WF: Elevated blood pressure in primary care varies in relation to circadian and seasonal changes. J Hum Hypertens 2008;22:755–760.
12.
Murakami S, Otsuka K, Kubo Y, Shinagawa M, Yamanaka T, Ohkawa S, Kitaura Y: Repeated ambulatory monitoring reveals a Monday morning surge in blood pressure in a community-dwelling population. Am J Hypertens 2004;17:1179–1183.
13.
Wilson SL, Poulter NR: The effect of non-steroidal anti-inflammatory drugs and other commonly used non-narcotic analgesics on blood pressure level in adults. J Hypertens 2006;24:1457–1469.
14.
Timmers HJLM, Buskers FGM, Wieling W, Karemaker JM, Lenders JWM: Long-term effects of unilateral carotid endarterectomy on arterial baroreflex function. Clin Auton Res 2004;14:72–79.
15.
UK-TIA Study Group: The United Kingdom transient ischaemic attack (UK-TIA) aspirin trial: final results. J Neurol Neurosurg Psychiatry 1991;54:1044–1054.
16.
European Carotid Surgery Trialists’ Collaborative Group: Randomised trial of endarterectomy for recently symptomatic carotid stenosis: final results of the MRC European Carotid Surgery Trial (ECST). Lancet 1998;351:1379–1387.
17.
Yong M, Diener HC, Kaste M, Mau J: Characteristics of blood pressure profiles as predictors of long-term outcome after acute ischemic stroke. Stroke 2005;36:2619–2625.
18.
Mena L, Pintos S, Queipo NV, Aizpura JA, Maestre G, Sulbaran T: A reliable index for the prognostic significance of blood pressure variability. J Hypertens 2005;23:505–511.
19.
McGraw KO, Wong SP: Forming inferences about some intraclass correlation coefficients. Psychol Methods 1996;1:30–46.
20.
Fleiss JL, Cohen J: The equivalence of weighted kappa and the intraclass correlation coefficient as measures of reliability. EBSCO 1973;33:613–619.
21.
ESPS Group: European Stroke Prevention Study. Stroke 1990;21:1122–1130.
22.
Howard SC, Rothwell PM: Regression dilution of systolic and diastolic blood pressure in patients with established cerebrovascular disease. J Clin Epidemiol 2003;56:1084–1091.
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2009
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