Baroreflex sensitivity in obesity: relationship with cardiac autonomic nervous system activity

Abstract

Objective: The aim of this study was to test the hypothesis that baroreflex sensitivity (BRS), assessed by indirect measurement of aortic pressure, is blunted in obesity. Additionally, the potential effect of cardiac autonomic nervous system (ANS) activity, aortic compliance, and metabolic parameters on BRS of obese subjects was investigated.

Research methods and procedures: A group of 30 women with BMI>30 kg/m2 and a group of 30 controls with BMI<25 kg/m2 were examined. BRS was estimated by the sequence technique, cardiac ANS activity by short-term spectral analysis of heart rate variability (HRV), and aortic compliance by the method of applanation tonometry.

Results: BRS was lower in obese women (9.18+/-3.77 vs. 19.63+/-9.16 ms/mm Hg, p<0.001). The median values (interquartile range) of the power of both the high-frequency and low-frequency components of the HRV were higher in the lean than in the obese participants [1079.2 (202.7 to 1716.9) vs. 224.1 (72.7 to 539.6) msec2, p=0.001 and 411.8 (199.3 to 798.0) vs. 235.8 (99.4 to 424.5) msec2, p=0.01 respectively]. Low-to-high-frequency ratio values were higher in the obese subjects [0.82 (0.47 to 2.1) vs. 0.57 (0.28 to 0.89), p=0.02]. Aortic augmentation values were not significantly different between lean and obese subjects. Multivariate analysis demonstrated a significant and independent association between BRS and age (p=0.003), BMI (p<0.001), and high-frequency power of HRV (p<0.001). These variables explained 72% of the variation of BRS values.

Discussion: BRS is severely reduced in obese subjects. BMI, age, and the parasympathetic nervous system activity are the main determinants of BRS. Baroreflex behavior is of clinical relevance because an attenuated BRS represents a negative prognostic factor in cardiovascular diseases, which are common in obesity.