dc.contributor.author	Madden, Jamie M.
dc.contributor.author	Li, Xia
dc.contributor.author	Kearney, Patricia M.
dc.contributor.author	Tilling, Kate
dc.contributor.author	Fitzgerald, Anthony P.
dc.contributor.funder	Health Research Board	en
dc.date.accessioned	2017-03-07T11:22:25Z
dc.date.available	2017-03-07T11:22:25Z
dc.date.issued	2017-02-02
dc.date.updated	2017-03-07T10:15:25Z
dc.description.abstract	Background: There are many examples of physiological processes that follow a circadian cycle and researchers are interested in alternative methods to illustrate and quantify this diurnal variation. Circadian blood pressure (BP) deserves additional attention given uncertainty relating to the prognostic significance of BP variability in relation to cardiovascular disease. However, the majority of studies exploring variability in ambulatory blood pressure monitoring (ABPM) collapse the data into single readings ignoring the temporal nature of the data. Advanced statistical techniques are required to explore complete variation over 24 h. Methods: We use piecewise linear splines in a mixed-effects model with a constraint to ensure periodicity as a novel application for modelling daily blood pressure. Data from the Mitchelstown Study, a cross-sectional study of Irish adults aged 47–73 years (n = 2047) was utilized. A subsample (1207) underwent 24-h ABPM. We compared patterns between those with and without evidence of subclinical target organ damage (microalbuminuria). Results: We were able to quantify the steepest rise and fall in SBP, which occurred just after waking (2.23 mmHg/30 min) and immediately after falling asleep (−1.93 mmHg/30 min) respectively. The variation about an individual’s trajectory over 24 h was 12.3 mmHg (standard deviation). On average those with microalbuminuria were found to have significantly higher SBP (7.6 mmHg, 95% CI 5.0–10.1) after adjustment for age, sex and BMI. Including an interaction term between each linear spline and microalbuminuria did not improve model fit. Conclusion: We have introduced a practical method for the analysis of ABPM where we can determine the rate of increase or decrease for different periods of the day. This may be particularly useful in examining chronotherapy effects of antihypertensive medication. It offers new measures of short-term BP variability as we can quantify the variation about an individual’s trajectory but also allows examination of the variation in slopes between individuals (random-effects).	en
dc.description.sponsorship	Health Research Board (PhD/2007/16; Research Grant Ref. HRC 2007/13)	en
dc.description.status	Peer reviewed	en
dc.description.version	Published Version	en
dc.format.mimetype	application/pdf	en
dc.identifier.citation	Madden, J. M., Li, X., Kearney, P. M., Tilling, K. and Fitzgerald, A. P. (2017) ‘Exploring diurnal variation using piecewise linear splines: an example using blood pressure’, Emerging Themes in Epidemiology, 14(1), pp. 1-11. doi:10.1186/s12982-017-0055-5	en
dc.identifier.doi	10.1186/s12982-017-0055-5
dc.identifier.endpage	11	en
dc.identifier.issn	1742-7622
dc.identifier.issued	1	en
dc.identifier.journaltitle	Emerging Themes In Epidemiology	en
dc.identifier.startpage	1	en
dc.identifier.uri	https://hdl.handle.net/10468/3752
dc.identifier.volume	14	en
dc.language.iso	en	en
dc.publisher	BioMed Central	en
dc.rights	© 2017, the Authors. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.	en
dc.rights.uri	http://creativecommons.org/licenses/by/4.0/	en
dc.subject	Circadian modeling	en
dc.subject	Mixed-effects models	en
dc.subject	Biostatistics	en
dc.subject	Blood pressure variability	en
dc.subject	Blood pressure patterns	en
dc.title	Exploring diurnal variation using piecewise linear splines: an example using blood pressure	en
dc.type	Article (peer-reviewed)	en

Exploring diurnal variation using piecewise linear splines: an example using blood pressure

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