The stability and repeatability of spontaneous sympathetic baroreflex sensitivity in healthy young individuals

Spontaneous sympathetic baroreflex sensitivity (BRS) is a valuable tool for assessing how well the baroreflex buffers beat-to-beat changes in blood pressure. However, there has yet to be a study involving appropriate statistical tests to examine the stability of sympathetic BRS within an experimental session and the repeatability between separate sessions. The aim of this study was to use intra-class correlations, ordinary least products regression, and Bland–Altman analyses to examine the stability and repeatability of spontaneous sympathetic BRS assessment. In addition, the influence of recording duration on values of BRS was assessed. In eighty-four healthy young individuals (49 males, 35 females), continuous measurements of blood pressure, heart rate and muscle sympathetic nerve activity (MSNA) were recorded for 10 min. In a subgroup of 13 participants (11 male, 2 female) the measurements were repeated on a separate day. Sympathetic BRS was quantified using MSNA burst incidence (BRS inc) and total MSNA (BRS total) for the first 5-min period, the second 5-min period, and a 2-min segment taken from the second 5-min period. Intra-class correlation coefficients indicated moderate stability in sympathetic BRS inc and BRS total between the first and second 5-min periods in males (BRS inc r = 0.63, BRS total r = 0.78) and females (BRS inc r = 0.61, BRS total r = 0.47) with no proportional bias, but with fixed bias for BRS inc in females. When comparing the first 5-min with the 2-min period (n = 76), the intra-class correlation coefficient indicated poor to moderate repeatability in sympathetic BRS inc and BRS total for males (BRS inc r = −0.01, BRS total r = 0.70) and females (BRS inc r = 0.46, BRS total r = 0.39). However, Bland–Altman analysis revealed a fixed bias for BRS total in males and proportional bias for BRS total in females, with lower BRS values for 5-min recordings. In the subgroup, intra-class correlations indicated moderate repeatability for measures of BRS inc (9 male, 2 female, r = 0.63) and BRS total (6 male, 2 female, r = 0.68) assessed using 5-min periods recorded on separate days. However, Bland–Altman analysis indicated proportional bias for BRS inc and fixed bias for BRS total. In conclusion, measures of spontaneous sympathetic BRS are moderately stable and repeatable within and between testing sessions in healthy young adults, provided that the same length of recording is used when making comparisons.