title: Autonomic responses to heat pain: Heart rate, skin conductance, and their relation to verbal ratings and stimulus intensity.
abstract: In human pain experiments, as well as in clinical settings, subjects are often asked to assess pain using scales (eg, numeric rating scales). Although most subjects have little difficulty in using these tools, some lack the necessary basic cognitive or motor skills (eg, paralyzed patients). Thus, the identification of appropriate nonverbal measures of pain has significant clinical relevance. In this study, we assessed heart rate (HR), skin conductance (SC), and verbal ratings in 39 healthy male subjects during the application of twelve 6-s heat stimuli of different intensities on the subjects' left forearm. Both HR and SC increased with more intense painful stimulation. However, HR but not SC, significantly correlated with pain ratings at the group level, suggesting that HR may be a better predictor of between-subject differences in pain than is SC. Conversely, changes in SC better predicted variations in ratings within a given individual, suggesting that it is more sensitive to relative changes in perception. The differences in findings derived from between- and within-subject analyses may result from greater within-subject variability in HR. We conclude that at least for male subjects, HR provides a better predictor of pain perception than SC, but that data should be averaged over several stimulus presentations to achieve consistent results. Nevertheless, variability among studies, and the indication that gender of both the subject and experimenter could influence autonomic results, lead us to advise caution in using autonomic or any other surrogate measures to infer pain in individuals who cannot adequately report their perception. Skin conductance is more sensitive to detect within-subject perceptual changes, but heart rate appears to better predict pain ratings at the group level.
authors.affiliation: Alan Edwards Centre for Research on Pain, McGill University, Montreal, Que., Canada Department of Neurology and Neurosurgery, McGill University, Montreal, Que., Canada Department of Psychiatry, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA Science College and Department of Biology, Concordia University, Montreal, Que., Canada Faculty of Dentistry, McGill University, Montreal, Que., Canada Department of Anesthesiology, McGill University, Montreal, Que., Canada.
authors.forename: Marco L
authors.initials: ML
authors.lastname: Loggia
authors.forename: Mylène
authors.initials: M
authors.lastname: Juneau
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Bushnell
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001341:Autonomic Nervous System / Q000503:physiopathology*; D005712:Galvanic Skin Response / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology*; D006358:Hot Temperature / Q000009:adverse effects*; D006801:Humans; D008297:Male; D010146:Pain / Q000209:etiology / Q000503:physiopathology*; D010147:Pain Measurement / Q000379:methods; D017288:Pain Threshold / Q000502:physiology*; D011601:Psychophysics / Q000379:methods; D011930:Reaction Time / Q000502:physiology; D055815:Young Adult