Functional Activity of the Autonomous Nervous System at Different Levels of Consciousness in Patients with a Brain Damage

Abstract

The purpose of the study — assessment of the level of consciousness in patients with a brain damage on the basis of electrophysiological examination of the functional state of the autonomous nervous system by recording parameters of the heart rate variability (HRV).Materials and Methods. The study included 77 patients on Day 20—50 after a traumatic brain injury, anoxic injury, consequences of acute cerebral circulation disorders. The following parameters of the HRV for a 5-minute recording were accepted as criteria of norm and pathology of the autonomous nervous system (ANS) activity: (1) parasympathetic hyperactivity (hypervagal state) values with 95% confidence intervals were recorded within the accepted values for (a) SDNN (standard deviation of normal to normal R-R intervals), [41.5 —149.3 ms]; (b) rMSSD (root-mean-square of the successive normal sinus R—R interval difference in ms), [42.4—175.0 ms];(c) pNN50% (percentage of successive normal sinus RR intervals >50 ms), [8.14—54.66%]; (d) SI (Baevsky stress index), [0—80 normalized units, n. u.]; (2) the sympathetic hyperactivity recordered within the range of values for (a) SDNN [4.54—13.30 ms]; (b) rMSSD [2.25— 5.77 ms]; (c) pNN50% [0—0.109%]; (d) SI >900 n. u.; (3) the normal value of ANS parameters were recordered within the range of values for (a) SDNN [13.31—41.4 ms]; (b) rMSSD [5.78—42.3 ms]; (c) pNN50% [0.110—8.1%]; (d) SI [80—900 n. u.]. For verification of the hypervagal state, sympathetic hyperactivity or normal state, at least 3 of 4 parameters should be within the specified limits.Results. In 40 (51.9%) of 77 patients examined after a brain damage, ANS functional activity parameters were within the range of pathological values. The sympathetic hyperactivity was identified in 34 patients, and in 6 cases the hypervagal state was diagnosed. Pathological parameters of HRV were found in 80% of patients with severe forms of unconsciousness (vegetative state, coma), and only in 20% of patients with normal consciousness.Conclusion.The computer analysis of the HRV is a necessary element of examination of patients with different levels of consciousness after a brain damage of a traumatic and non-traumatic genesis. The frequency of pathological changes in the functional state of the autonomous nervous system increases significantly in groups of patients from the normal level of consciousness to the state of minimal consciousness, vegetative state, and coma. The sympathetic hyperactivity is the main type of ANS pathology in the groups of patients with minimal consciousness, in the vegetative state, and coma.

Keywords

• autonomous nervous system
• heart rate variability
• minimal consciousness syndrome
• vegetative state