Autonomic nervous system activity in dipper and non-dipper essential hypertensive patients. What about sex differences?

Objectives To compare the autonomic nervous system activity indexes obtained from photoplethysmography in dipper and non-dipper hypertensive patients and to seek a potential influence of sex on the relation between autonomic nervous system and the nocturnal decrease in blood pressure. Methods We studied 245 hypertensive patients, who underwent 24 h ambulatory blood pressure monitoring (ABPM), photoplethysmographic blood pressure recording, and echocardiography. Non-dipping patients were defined as those whose nocturnal decrease in systolic blood pressure (SBP), diastolic blood pressure (DBP), or both was less than 10% of the daytime blood pressure. Spectral powers of SBP, DBP and heart rate were obtained from photoplethysmographic recordings over three main frequency bands: very low frequency (0.005-0.05 Hz), low frequency (0.05-0.14 Hz) and high frequency (0.14-0.40 Hz). Results Because their ABPM were normal (less than 135/ 85 mmHg; n = 33), of poor quality (n = 22) or performed at a period too far from the photoplethysmographic recording (n = 17), 66 patients were excluded from the analysis. The remaining 179 patients comprised 117 dippers and 62 non-dippers. The groups did not differ regarding clinical and echocardiographic characteristics, irrespective of sex. Low-frequency spectral powers were significantly lower in non-dippers than in dippers, whatever the signal, whereas high-frequency spectral powers did not differ significantly between the groups. The nocturnal decrease in blood pressure increased with increasing low-frequency spectral powers, but was negatively correlated with high-frequency spectral powers. Multivariate linear regression analysis identified low-frequency spectral power of SBP and clinic DBP as independent factors determining the decrease in blood pressure. After adjustment for all significant covariates, the odds of being a non-dipper did not differ between men and women. Conclusion A non-dipper profile seemed to be associated, in both men and women, with lower low-frequency spectral powers compared with those in dippers, suggesting impaired sympathetic arterial modulation.