Heart Rate Variability as an Indicator of Nociceptive Pain in Disorders of Consciousness?

J Pain Symptom Manage. 2019 Jan;57(1):47-56. doi: 10.1016/j.jpainsymman.2018.09.016. Epub 2018 Sep 27.


Context: Heart rate variability is thought to reflect the affective and physiological aspects of pain and is emerging as a possible descriptor of the functional brain organization contributing to homeostasis.

Objectives: To investigate whether the short-term Complexity Index (CIs), a measure of heart rate variability complexity is useful to discriminate responses to potentially noxious and nonnoxious stimulation in patients with different levels of consciousness.

Methods: Twenty-two patients (11 minimally conscious state [MCS], 11 vegetative state/unresponsive wakefulness syndrome [VS/UWS]) and 14 healthy controls (HC) were enrolled. We recorded the electrocardiographic response and calculated the CIs before (baseline), during, and after nonnoxious and noxious stimulation. Mann-Whitney and Wilcoxon's tests were used to investigate differences in CIs according to the level of consciousness (i.e., HC vs. patients and VS/UWS vs. MCS) and the three conditions (i.e., baseline, nonnoxious, noxious). The correlation between the three conditions and the Coma Recovery Scale-Revised was investigated by Spearman's correlations.

Results: We observed higher CIs values in HC as compared with patients during the baseline (P < 0.034) and after the noxious stimulation (P < 0.0001). We also found higher values in MCS versus VS/UWS patients after the noxious condition (P < 0.001) and lower values in the noxious versus nonnoxious condition solely for the VS/UWS group (P < 0.007). A correlation was found between CIs in noxious condition and Coma Recovery Scale-Revised scores.

Conclusion: Our results suggest a less complex autonomic response to noxious stimuli in VS/UWS patients. Such method may help to better understand sympathovagal response to potentially painful stimulation in brain-injured patients.

Keywords: Pain; consciousness; heart rate; minimally conscious state; nociception; unresponsive wakefulness syndrome.

Publication types

  • Multicenter Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Consciousness Disorders / complications*
  • Consciousness Disorders / diagnosis
  • Consciousness Disorders / physiopathology
  • Electrocardiography*
  • Female
  • Heart Rate*
  • Humans
  • Male
  • Middle Aged
  • Nociception
  • Nociceptive Pain / complications*
  • Nociceptive Pain / diagnosis*
  • Nociceptive Pain / physiopathology
  • Pain Measurement / methods*
  • Physical Stimulation
  • Young Adult