gms | German Medical Science

Objective: Heart rate variability (HRV) is defined as variation of the beat-to-beat R-R time interval between consecutive heart beats in the electrocardiogram (ECG). HRV reflects autonomic control of the cardio-vascular system, which may be impaired in patients with lesions of brain stem areas associated with autonomic control functions. The aim of the present study was to compare the HRV between (1) healthy volunteers, (2) comatose patients without and (3) comatose patients with a brain stem lesion as verfied by MRI and (4) patients exhibiting the clinical criteria of brain death.

Methods: HRV was assessed in 11 healthy volunteers, in 20 comatose patients without a brain stem lesion in the MRI, in 24 comatose patients with a brain stem lesion verified by MRI and in 21 patients fulfilling the clinical criteria of brain death. The ECG was digitized by means of an analog-to-digital converter and sampled for a period of 30 minutes once a day (500 Hz sampling rate, 12 bit resolution). For each patient, consecutive normal R-R time intervals [s] were determined from these time-series and used to calculate the standard deviation of beat-to-beat intervals (SDNN) and the root mean square of successive differences (RMSSD), two common HRV parameters.

Results: Patients with a brain stem lesion showed a marked reduction of the HRV-paramerters (SDNN=0.019±0.018, RMSSD=0.018) as compared to comatose patients without a brain stem lesion (SDNN=0.031±0.027, RMSSD=0.032) and healthy volunteers (SDNN=0.080±0.028, RMSSD=0.059). HRV was further reduced in patients fulfilling the clinical criteria of brain death (SDNN=0.0056±0.0054, RMSSD=0.003).

Conclusions: Our results show that HRV is markedly reduced in comatose patients with brain stem lesions and further reduced in patients fulfilling the criteria of brain death. Therefore, the continuous quantitative assessment of different HRV-parameters constitutes a promising new approach for monitoring patients with lesions in the brain stem.