Blood pressure and heart rate fluctuations and baroreflex control: insights from data before and after brain death

摘要

In this paper we report on the changes in blood pressure and heart rate variability and baroreflex function observed in 11 comatose patients before and after brain death. Spontaneous variability of systolic blood pressure (SBP) and pulse interval (PI, the reciprocal of heart-rate) were estimated by spectral analysis. Spontaneous baroreflex sensitivity (BRS) and baroreflex effectiveness index (BEI) by the sequence technique.Brain death was associated with significant spectral changes, including a generalized reduction in PI spectra and a decrease of the 0.1 Hz power in SBP spectra. No change was observed in the blood pressure power at the respiratory frequency. BRS and BEI, values showed a high individual dispersion before brain death - although the group average was close to normal values. Five patients even showed BRS values markedly higher than normal. In all subjects the SBP/PI spontaneous sequences from which BRS was estimated almost completely disappeared after brain death.These changes occurring in the transition from the state of impending brain death to the complete inactivity of the brain stem provide an additional support to the hypothesis of a main contribution of the baroreflex to the genesis of the respiratory oscillation in the heart rate spectra and of the 0.1 Hz rhythm on both blood pressure and heart rate variability.