Regardless of the time of day that it is measured—whether it be during the morning, the afternoon, the evening, and night time—there is a parallel, incremental, upward shift in blood pressure in the vast majority of hypertensive patients when compared with normotensive individuals. Intuitively it would therefore seem appropriate that strategies to reduce blood pressure should be effective throughout the 24 hour period in a consistent fashion (fig 1).

Epidemiological evidence reveals that the highest number of cardiovascular events occur in the early morning period and this corresponds to the time when there is a surge in blood pressure.1 Blood pressure is not necessarily at its highest at this point, but there is a sharp rise from the inherently low levels during the night time period to those around the time of wakening. It should be appreciated, however, that there are also other events that occur at this time such as changes in platelet aggregability and catecholamines. Importantly, as most patients take their antihypertensive medication in the morning, the surge in blood pressure also corresponds to the period with minimum pharmacological cover—that is, 24 hours post dose with a once a day regimen.

Epidemiological evidence also shows that blood pressure variability itself is an independent determinant of target organ damage. Thus, for any given level of average blood pressure, where variability around that mean is greater, the patient is likely to be more susceptible to evidence of hypertension related end organ damage.1 Furthermore, there is evidence to support the contention that drug induced blood pressure variability may also be deleterious.

In patients who fail to show the “normal” circadian dip in night time blood pressure there is evidence of increased cardiovascular risk.1 Initially this was demonstrated in …