Monitoring the brain-stem state through the assessment of the baroreceptor-heart rate reflex in critically brain-injured patients

The aim of this study was to evaluate whether the analysis of cardiovascular dynamics and the assessment of the baroreceptor-heart rate reflex can be used to derive information on the functionality of the cardiomotor brain-stem centers and whether this information may facilitate the diagnosis of brain death. We estimated during impending brain death in 11 comatose patients hospitalized in ICU (1) spontaneous variability of systolic and diastolic blood pressure (SBP and DBP) and pulse interval (PI, the reciprocal of heart-rate) by spectral analysis; and (2) 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 and DBP spectra. BRS and BEI, close to normal values just before brain death, dropped to 0 after the brain death event. These changes - likely to reflect the cessation of activity of the cardiovascular brainstem centers - suggest that techniques for blood pressure and heart rate spectral analysis and for the dynamic estimation of spontaneous baroreflex control of the heart can be used for monitoring the brain-stem state in ICU and may complement the traditional assessment of brain-stem death.