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Spontaneous sympathetic baroreflex sensitivity is correlated with cardiac baroreflex sensitivity in healthy, young individuals

      Aim. Low baroreflex sensitivity (BRS) is associated with elevated cardiovascular risk. However, the evidence is based primarily on measurements of cardiac BRS. It cannot be assumed that cardiac or sympathetic BRS alone represent a true reflection of baroreflex control of blood pressure. The aim of this study was to examine the relationship between sympathetic and cardiac BRS in healthy, young individuals. Methods. Continuous measurements of blood pressure, heart rate and muscle sympathetic nerve activity (MSNA) were made under resting conditions in 50 healthy individuals (18-28 yrs). Cardiac BRS was quantified by plotting RR interval against systolic blood pressure using the sequence method. Sympathetic BRS was quantified by plotting MSNA burst incidence against diastolic pressure. Results. Significant baroreflex slopes were obtained for 42 participants. A significant positive correlation was found between cardiac and sympathetic BRS (r = 0.32, p = 0.038). When cardiac baroreflex sensitivities were divided into ‘up’ and ‘down’ sequences, a significant correlation with sympathetic BRS was observed for ‘down’ (r = 0.38, p = 0.012) but not ‘up’ sequences (r = 0.23, p = 0.146). In 29 participants significant baroreflex slopes were obtained when plotting total MSNA against diastolic pressure. In this subset, a significant correlation was observed between sympathetic BRS and cardiac BRS (r = 0.39, p = 0.036) and cardiac BRS ‘up’ (r = 0.37, p = 0.047). Conclusion. In healthy, young individuals the effectiveness of the baroreflex appears to be consistent between cardiac and sympathetic arms within individuals. This suggests that cardiac BRS may be appropriate for estimating overall baroreflex function where measurements of sympathetic outflow are not feasible. This relationship warrants investigation in clinical populations.
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