↓ Skip to main content

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

Overview of attention for article published in Emerging Themes in Epidemiology, February 2017
Altmetric Badge


1 Dimensions

Readers on

21 Mendeley
You are seeing a free-to-access but limited selection of the activity Altmetric has collected about this research output. Click here to find out more.
Exploring diurnal variation using piecewise linear splines: an example using blood pressure
Published in
Emerging Themes in Epidemiology, February 2017
DOI 10.1186/s12982-017-0055-5
Pubmed ID

Jamie M. Madden, Xia Li, Patricia M. Kearney, Kate Tilling, Anthony P. Fitzgerald


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. 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). 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. 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).

Mendeley readers

The data shown below were compiled from readership statistics for 21 Mendeley readers of this research output. Click here to see the associated Mendeley record.

Geographical breakdown

Country Count As %
Israel 1 5%
Denmark 1 5%
Unknown 19 90%

Demographic breakdown

Readers by professional status Count As %
Student > Ph. D. Student 5 24%
Professor > Associate Professor 4 19%
Researcher 4 19%
Student > Master 2 10%
Librarian 2 10%
Other 3 14%
Unknown 1 5%
Readers by discipline Count As %
Medicine and Dentistry 9 43%
Neuroscience 2 10%
Biochemistry, Genetics and Molecular Biology 2 10%
Engineering 2 10%
Psychology 1 5%
Other 4 19%
Unknown 1 5%