Ambulatory blood pressure monitoring for clinical applications and basic science

Monitoring for spans longer than 24 hours, preferably for 7 days at the outset, has been advocated to obtain more reliable estimates of the circadian characteristics of blood pressure and heart rate. Herein, using data from a chronotherapy trial, we address the desirability of complementing the global analysis of the entire record by the computation of daily sphygmochrons to gain a better assessment of the day-to-day variability in the circadian patterns of these variables. An algorithm for defining optimal spans covering approximately a day (while using all data in a record) is developed and implemented as a script in R. Combined with criteria to determine whether the data in a given span are sufficient to yield reliable estimates of the circadian characteristics of blood pressure and heart rate, results from this approach are compared by means of Bland-Altman plots to those stemming from considering 24-hour spans. Applications of daily sphygmochrons are wide-ranging, in patients as well as in healthy people, for clinical applications, for health maintenance and surveillance, for a better understanding of how blood pressure and heart rate are affected by a variety of factors in everyday life, such as nutrition, exercise, smoking, salt and alcohol intake, and for learning how human physiology is influenced by space-terrestrial weather.