Blood pressure circadian rhythm in essential hypertension.

1. Both systolic and diastolic blood pressure show a well defined circadian variation in ambulatory hypertensive subjects. 2. Blood pressure is highest in the mid-morning (10.00 hours) and lowest during sleep at 03.00 hours. 3. Treatment with oxprenolol (taken during the day) reduces daytime blood pressure but is less effective during the night and early morning.