[Nyctohemeral changes of blood pressure. Diagnostic and prognostic value]

The blood pressure shows circadian variation in normal subjects with higher diurnal than nocturnal values: the difference between day and night time blood pressure is about 10-20 mmHg for systolic and for diastolic blood pressure. These variations are mainly related to physical and/or psychosensorial stress: the physician is himself a cause of increased blood pressure (the "white coat" effect). The degree of the nocturnal decrease in blood pressure which is maximal 2 and 3 o'clock is related to the quality and depth of sleep. The nocturnal decrease is followed by an increase in blood pressure when the person wakes up (early morning peak). Diagnostic signs: a physiological inversion of the circadian rhythm may be observed in people who sleep during the daytime and work at night. There would seem to be less of a nocturnal fall in black persons in the United States. Some pathological conditions can inverse or at least disturb the ciacadian variation: apart from hypertension, this has been reported in autonomic nervous system disease, in diabetics with autonomic neuropathy in some elderly patients, in Cushing's syndrome, after cardiac transplantation, etc... In hypertensives, the lack of nocturnal decrease of the blood pressure or an inversion in circadian rhythm should be looked for in severe and secondary hypertension such as associated with pheochromocytoma, or in renal dialysis patients. In toxaemia of pregnancy, this abnormality may herald an eclamptic crisis. Prognostic signs: in normotensives (especially in black persons) and hypertensives, inversion of the circadian rhythm is associated with more severe left ventricular hypertrophy and a higher morbidity.