[The day-night rhythm in the 24-hour blood pressure profile. A possibility of distinguishing between primary and secondary hypertension?].
Automatic 24-hour blood pressure measurements were undertaken in 60 patients with primary systemic hypertension (24 women, 36 men; mean age 51 +/- 23 years) and 105 with secondary hypertension (36 women, 69 men; mean age 51 +/- 24 years). The aim of the study was to ascertain whether the absence of a day-night blood pressure rhythm is a reliable sign that the hypertension is secondary or whether it can also occur in primary hypertension. None of the patients was receiving any treatment. Day-night rhythm was abolished in 10 patients with primary hypertension (16%) and in 65 of those with secondary hypertension (62%). But an analysis of 11 case reports indicated that in an individual case there is no absolute rule. While absence of the day-night rhythm points to secondary hypertension, there are numerous exceptions.