Circadian blood pressure variations in endocrine disorders

Circadian rhythm of blood pressure and of heart rate was studied in patients with hyperthyroidism (n = 10), pheochromocytoma (n = 8), primary hyperaldosteronism (n = 7), and in a control group of essential hypertensive patients (n = 18) and of normotensive healthy subjects (n = 11). 24-hour blood pressure was monitored non-invasively using SpaceLabs (SL 90207) with 8-min intervals in the daytime (8 a.m. to 10 p.m.) and 30-min intervals during night-time (10 p.m. to 8 a.m.). To characterize circadian blood pressure rhythm the difference between the mean blood pressure during daytime and that during night-time was calculated. In patients with hyperthyroidism the day-night difference of the systolic and diastolic blood pressure and of the heart rate was significantly reduced when compared to the normotensive control group (p < 0.05). The day-night difference of the systolic and diastolic blood pressure was significantly lower in the group with pheochromocytoma and hyperthyroidism than in the essential hypertensive controls (p < 0.05); the day-night difference of the heart rate was similar. In the patients with primary hyperaldosteronism the day-night differences of the systolic and diastolic blood pressure and of the heart rate was similar to those in essential hypertensive controls. We conclude that endocrine disorders affecting sympathetic activity like pheochromocytoma or hyperthyroidism influence the circadian blood pressure rhythm, whereas the renin-aldosterone-system has no major impact on the diurnal blood pressure variation. The results therefore support the hypothesis that circadian blood pressure variation is mainly mediated by a modulation of the sympathetic tone.