Relationship between 24-hour arterial pressure and heart rate variation in normotensives, hypertensives and patients with Shy-Drager syndrome.

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Abstract
To investigate a relation between circadian blood pressure and heart rate variation, intra-arterial blood pressure (BP) and heart rate (HR) were recorded during 24 hours in 53 untreated essential hypertensives (EH), 8 secondary hypertensives, 10 normotensives (NT), and 3 patients with Shy-Drager syndrome. Values of systolic BP (SBP) and HR were sampled at about 10 second intervals throughout the 24-hour to calculate the coefficient of correlation between SBP and HR (rSBP-HR). A significant positive correlation was found between SBP and HR levels in each subject of EH with WHO stage I and II, along with NT (averge rSBP-HR =0.59,0.40,and 0.54 respectively, p < 0.001). Low coefficients of correlation were found in the EH with WHO Stage III (r = 0.16) and the patients with pheochromocytoma (r = 0.05). In contrast, a significant negative correlation was found in the patients with Shy-Drager syndrome (r = -0.44,p < 0.001). Since HR is controlled mainly by the autonomic nervous system (ANS), the results suggest that the circadian variation of SBP is also mainly controlled by the ANS in the subjects with high rSBP-HR and that of SBP controlled by the other factors in subjects with low rSBP-HR.