Comparison of baroreflex sensitivity indices with standard tests of autonomic nervous system function

In order to further evaluate clinical usefulness of α- and β-adrenergic components of the baroreflex sensitivity (BRS) index, the aim of this study was to compare them to standardized measures of the autonomic dysfunction.

In 275 participants (mean age 40.57 ± 15.19, range 18 to 89 years, 76.4% females) referred for testing of the autonomic nervous system, α-BRSa, β-BRSa and BRSv were compared to heart rate (HR) and blood pressure (BP) values, adrenergic and cardiovagal indices of the Composite Autonomic Severity Score (CASS) and heart rate variability (HRV) parameters.

α-BRSa showed statistically significant positive correlation with HR in the supine position and negative with the adrenergic index. β-BRSa showed statistically significant negative correlation with tests for parasympathetic nervous system function. BRSv showed statistically significant negative correlation with all HR and BP parameters and positive with all HRV parameters. In a univariable logistic regression analysis, α-BRSa was a negative predictor (Exp(B) 0.866, 95% CI 0.782-0.959, p = 0.006, respectively) of the pathological adrenergic index. To differentiate between subjects with normal and pathological adrenergic index, the optimal cutoff for α-BRSa was found to be 6.741, which gave a sensitivity of 61.0% and a specificity of 56.0%.

BRSa indices showed a good correlation with standard measures of ANS function. The most promising test was α-BRSa, which performed well as a α adrenergic receptors mediated sympathetic nervous system marker.