[Circadian rhythm of blood pressure. Importance of the severity and not the cause of arterial hypertension].

Recent work have raised the possibility of a lack of circadian blood pressure variability in secondary hypertension. To test this hypothesis, we compared 11 patients with renovascular hypertension (RVH) and 11 essential hypertensive patients (EH) matched for sex, age, body weight, height and the average level of SBP from 7 a.m. to 10 p.m. monitored every 15 minutes with a Spacelabs 5200 device. All patients had BP monitored during 24 hours, inside the hospital, after all anti-hypertensive drugs were discontinued for more than 5 days. Paired t test revealed no difference between the two groups. Differences (D - N) between average day time (7 a.m.-10 p.m.) and night time (10 p.m.-7 a.m.) systolic and diastolic BP were not different in the two groups. (Table: see text). To test the influence of BP level on circadian BP variation, we studied the correlation between the difference in day and night average SBP, as a % of average day time SBP, and the average day time SBP in 25 normal subjects and 64 hypertensive patients without treatment. A weak but significant correlation was demonstrated (r = -0.29; p less than 0.01). The higher the average day time SPB, the lower the difference between day and night. In conclusion, circadian variation of BP is not different between essential and renovascular hypertensive patients, but there is a trend to a smaller variation in patients with the higher BP.