CIRCADIAN VARIATION OF HEMODYNAMICS IN PATIENTS WITH ESSENTIAL-HYPERTENSION - COMPARISON BETWEEN EARLY-MORNING AND EVENING

Objective: An increased incidence of cardiovascular accidents in the m orning has been reported, but the reason why is not clear. We measured 24-h haemodynamics and focused on its change in the morning. Design: To study the circadian variation of haemodynamics, we recorded 24-h di rect blood pressure and electrocardiogram using a telemetry method, in 21 untreated inpatients with essential hypertension, and measured car diac output using the dye-dilution method in the morning, in the eveni ng and during sleep. We also determined the beat-to-beat cardiac outpu t (using the pulse-contour method), the total peripheral resistance an d the ratio of low- to high-frequency components (using power spectral analysis of the R-R interval during 24 h), and made comparisons betwe en morning and evening values. Results: Both systolic and diastolic bl ood pressure increased rapidly in the early morning. Although the comp arison of blood pressure between morning and evening showed no differe nce, total peripheral resistance and low- to high-frequency ratio were significantly higher in the morning than in the evening, but cardiac output was lower in the morning. Conclusions: Sympathetic nervous acti vity and vascular resistance seem to be higher in the morning than in the evening, and these haemodynamic changes may stress the cardiovascu lar system.