Quantification of autonomic activity in the brainstem in normal, comatose and brain dead subjects using heart rate variability.

The heart rate variability is defined as variation in distance between sequential ventricular complexes in the electrocardiogram and can be given in percent by referring the standard deviation to the average values of heart rate. The bivariate distribution of heart rate variability and of heart rate shows a discrimination of the group of comatose patients from brain dead subjects and normals.