Objective: To assess, in a population-based approach, sympathetic nervous system activity by the use of power spectral analysis of heart rate variability, in normotension, white-coat hypertension, masked hypertension and sustained hypertension.
Methods: The electrocardiographic RR interval was registered in the supine and standing positions and the low-frequency and high-frequency components of its variability were quantified. Cut-off values of 140/90 mmHg for conventional blood pressure and 135/85 mmHg for daytime ambulatory blood pressure were used to define the four blood pressure groups.
Results: After exclusion of patients with diabetes, myocardial infarction or treated hypertension, 1485 subjects with complete data remained for the analysis in the supine position. Age averaged 39 +/- 14 years; 54% were women. Conventional and ambulatory blood pressure averaged, respectively, 122 +/- 16/79 +/- 11 mmHg and 124 +/- 12/77 +/- 8 mmHg. After adjusting for demographic, anthropometric and lifestyle characteristics, the low-frequency to high-frequency ratio (geometric mean) averaged 0.81 in normotension and was significantly higher in white-coat hypertension (1.11; P < 0.001), based on a higher low-frequency component and a lower high-frequency component (P < 0.01). This ratio was not significantly different between normotension, masked hypertension (0.97) and sustained hypertension (0.93). The adjusted standing-to-supine ratio of the high-frequency component (geometric mean) was significantly higher in sustained hypertension (0.50) than in normotension (0.39; P < 0.01), but not in white-coat (0.40) and masked hypertension (0.45).
Conclusion: The findings at rest are compatible with increased sympathetic activity and decreased parasympathetic modulation in white-coat hypertension, with normal autonomic cardiac regulation in masked and sustained hypertension. In addition, sustained hypertension is characterized by a blunted decrease of the high-frequency component on standing.