Is the EEG cyclic alternating pattern a true autonomous entity? Analytic study in a case of post-traumatic coma with good prognosis.

The cyclic alternating pattern (CAP) characterizes stage-II coma according to Fischgold and Mathis. Its evolution and prognostic value are still uncertain. An analytic investigation of CAP and its components (phase A of greater arousal and phase B of lesser arousal) was conducted on a patient with post-traumatic coma who completely recovered. The relationships between this type of pattern and the stages of physiologic sleep were investigated during four prolonged night recordings taken at regular intervals. The evolution of CAP in post-traumatic coma is compared with the development of CAP observed in Creutzfeldt-Jakob disease. The hypothesis is suggested that CAP may be related to other cyclic phenomena, especially the Lundberg B-type CSF pressure waves. According to this assumption, in a coma with CAP, mechanisms for the organization of arousal, which are not known but persist up to the threshold of death, could still be acting. In sleep these same mechanisms are supposed to be integrated with others, more sophisticated and less resistant to pathogenic injuries.