Even if these factors are controlled, blood pressure is subject to biological variation from beat to beat, minute to minute, and day to day. Each blood pressure measurement is therefore analogous to a single sample from a population of blood pressures. However, it is a patient’s mean blood pressure over months and years that are thought to determine his or her risk of cardiovascular disease. In order to increase the precision of the estimated blood pressure, clinical diagnosis is based on the average of MK-2206 2HCl measurements taken after resting for 5 minutes in a non-stimulating environment. Despite such standardized procedures, BP remains highly variable both within and between individuals. However, both this accepted fact and the ease of describing such variability are not well appreciated. Understanding to what extent BP is variable is very important since the large variability of BP impacts diagnosis of hypertension, clinical management of elevated BP and number of drugs prescribed to achieve ‘‘BP control’’. BP variability has been shown to increase with increasing blood pressure and correlate with target-organ damage, independent of absolute BP values. However, the importance of BP variability as an independent risk factor remains controversial. In a study by Pierdomenico S et al, after adjustment for other covariates in a Cox multivariate analysis, the adverse prognostic impact of high BP variability was no longer evident. In fact the prognostic value of BP variability has not been tested by proper longitudinal studies and the few available ones are limited by small study size, short follow up or conclusions based on surrogate markers rather than on the incidence of hard end points,Niraparib such as cardiovascular events. A better exploration of BP variability and of the influence of drugs on BP variability may improve understanding of the mechanisms involved in BP changes induced by drugs. We know that drugs reduce cardiovascular risks, in different ways and to various extents, by different mechanisms; however what is surprising is that we do not clearly know the impact of these drugs on BP variability. We have used the availability of a large amount of resting research setting BP data from 33,611 patients, accumulated as part of two systematic reviews, to answer whether thiazides affect BP variability and describe some other characteristics of BP variability.