Diurnal Rhythms, the Renin-Angiotensin System and Antihypertensive Therapy

Michael Schachter


Br J Cardiol. 2004;11(4) 

In This Article

Circadian Changes in Blood Pressure and Heart Rate

Although it has long been known that blood pressure fluctuates during the day, the amount of data relating to this has hugely increased in recent years since ambulatory blood pressure monitoring became clinically practicable. This has confirmed a consistent pattern in most normotensive and hypertensive subjects, though of course the overall levels are higher in the latter (see figure 1).[1,2] We know that:

  • Highest levels of blood pressure occur after 10 am with a peak around noon but often with a plateau extending to 6 pm.

  • Leading up to this, there is a rise in pressure from the time of waking or before (about 6 am), with the pressure rising by up to 20/15 mmHg in most people.

  • There is a decline in pressure of 10-20% in the late evening and on going to sleep, with a nadir in blood pressure at about 3 am.

Stylised representation of 24-hour blood pressure rhythm in normotensive (lower curve) and hypertensive (upper curve) individuals. The rectangle indicates period of maximum risk for cardiovascular events.

Of course this can be modified by changes in patterns of activity, for instance in shift workers, and by other factors such as strenuous exercise and anxiety (as in the white-coat syndrome). This pattern is also modified in some hypertensive patients, who can experience:

  • The loss of nocturnal 'dipping', that is to say the decline in blood pressure is less than 10% at night and may be almost non-existent. This is associated with increased target-organ damage and enhanced risk of cardiovascular events.[3,4]

  • Extreme dipping, with reductions in pressure of more than 20% in night-time pressures. This too is thought to be harmful, especially with regard to stroke, but this has yet to be fully confirmed.[5]

  • The morning rise or 'surge' in blood pressure may be exaggerated, not necessarily in the rate of rise in pressure but rather in the level attained.

Broadly, changes in heart rate parallel those in blood pressure.

These changes are influenced by many factors apart from actual activity, including age, gender and ethnicity. For instance, the nocturnal dip is generally diminished in black individuals and older individuals from all races.[6] On the other hand it may be greater in women than in men.