Short-term stability of baroreflex sensitivity

We studied the within-session stability of the noninvasive baroreflex sensitivity (BRS) in 23 young healthy male subjects, by analyzing continuous 8-minute recordings, and comparing the results of the first and second 4-minute periods. BRS recordings were made under 15/min (0.25 Hz) metronome respiration. BRS was computed by integrating the spectral systolic blood pressure to inter-beat-interval (IBI) transfer function in the 0.05-0.10 Hz band. For the group, BRS and mean IBI in the first and the second 4-minute period (mean+SD: 8.8±6.0 vs. 8.2±6. 5 ms/mmHg, and 927±151 vs. 938±153 ms, respectively) did not differ significantly. However, Bland-Altman plots (differences against averages) revealed rather large individual BRS differences between the first and second half of the recording period: the absolute values of the differences were 34.6±30% of the average (range 0.8-111.2%, median 22.7%). BRS differences were not related to changes in mean IBI. We conclude that for reliable BRS assessment a recording period of 4 minutes is too short. A continuous 8-minute recording with metronome respiration is preferable and feasible