Heart-rate variability in brain-damaged adults.

To test whether or not the characteristics of the adult heart-rate reflect the condition of the central nervous system (as they seem to do in the fetus), ten patients with neurological deficits of acute onset were studied. No patients had received drugs and none was hypoxic. The findings indicate that the normal cyclic changes in heart-rate are reduced in the presence of severe brain damage. Variability decreases rapidly if intracranial pressure rises, and the rate of return of variability reflects the subsequent state of neuronal function, even when intracranial pressure has been restored to normal. In this limited setting, then, it appears that heart-rate variability may reflect the functional state of the central nervous system.