Blood pressure and heart rate variability and baroreflex sensitivity before and after brain death

Objectives-To evaluate spontaneous blood pressure and heart rate variabilit y and spontaneous baroreflex sensitivity before and after brain death. Methods-Spontaneous variability of arterial blood pressure and heart rate-e stimated by power spectra of systolic (SBP) and diastolic blood pressure (D BP) and pulse interval (Pl)-and spontaneous baroreflex sensitivity (BRS)-es timated by the alpha index and the sequence technique-were evaluated in 11 patients twice: shortly before and 1 hour after the onset of brain death. Results-Significant spectral changes occurred after brain death: a general power reduction in PI spectra; a shift of SBP, DBP and PI powers toward the lower frequencies, resulting in a greater slope of the "1/f" spectral tren ds; and a marked reduction of SBP and DBP powers (-93%) and of SBP-PI coher ence (-63%) at 0.1 Hz. The estimated average BRS was relatively high before brain death (around 11 ms/mm Hg), and fell close to 0 or even was not dete ctable at all after brain death. Conclusions-Parameters describing spontaneous blood pressure and heart rate variability and indexes reflecting the baroreflex function, which were rel atively normal up to a few hours before brain death, underwent marked chang es with the onset of brain death. All the changes found are likely to refle ct the cessation of activity of the cardiovascular brain stem centres. Thes e findings indicate that techniques of blood pressure and heart rate spectr al analysis and of dynamic assessment of baroreflex sensitivity may be usef ul to complement the diagnosis of brain stem death.