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Pain Rep. 2017 Nov 15;2(6):e626. doi: 10.1097/PR9.0000000000000626. eCollection 2017 Nov.

A tonic heat test stimulus yields a larger and more reliable conditioned pain modulation effect compared to a phasic heat test stimulus.

Lie MU1,2, Matre D3, Hansson P4,5, Stubhaug A5,6, Zwart JA1,6,7, Nilsen KB1,3,7,8.

Author information

1
Research and Communication Unit for Musculoskeletal Health (FORMI), Oslo University Hospital, Oslo, Norway.
2
Faculty of Health Science, Oslo and Akershus University College of Applied Sciences, Oslo, Norway.
3
Department of Work Psychology and Physiology, National Institute of Occupational Health, Oslo, Norway.
4
Department of Molecular Medicine and Surgery, Karolinska Institutet, Stockholm, Sweden.
5
Department of Pain Management and Research, Division of Emergencies and Critical Care, Oslo University Hospital, Oslo, Norway.
6
Faculty of Medicine, University of Oslo, Oslo, Norway.
7
Department of Neurology, Oslo University Hospital, Oslo, Norway.
8
Department of Neuromedicine and Movement Science, Norwegian University of Science and Technology, Trondheim, Norway.

Abstract

Introduction:

The interest in conditioned pain modulation (CPM) as a clinical tool for measuring endogenously induced analgesia is increasing. There is, however, large variation in the CPM methodology, hindering comparison of results across studies. Research comparing different CPM protocols is needed in order to obtain a standardized test paradigm.

Objectives:

The aim of the study was to assess whether a protocol with phasic heat stimuli as test-stimulus is preferable to a protocol with tonic heat stimulus as test-stimulus.

Methods:

In this experimental crossover study, we compared 2 CPM protocols with different test-stimulus; one with tonic test-stimulus (constant heat stimulus of 120-second duration) and one with phasic test-stimuli (3 heat stimulations of 5 seconds duration separated by 10 seconds). Conditioning stimulus was a 7°C water bath in parallel with the test-stimulus. Twenty-four healthy volunteers were assessed on 2 occasions with minimum 1 week apart. Differences in the magnitude and test-retest reliability of the CPM effect in the 2 protocols were investigated with repeated-measures analysis of variance and by relative and absolute reliability indices.

Results:

The protocol with tonic test-stimulus induced a significantly larger CPM effect compared to the protocol with phasic test-stimuli (P < 0.001). Fair and good relative reliability was found with the phasic and tonic test-stimuli, respectively. Absolute reliability indices showed large intraindividual variability from session to session in both protocols.

Conclusion:

The present study shows that a CPM protocol with a tonic test-stimulus is preferable to a protocol with phasic test-stimuli. However, we emphasize that one should be cautious to use the CPM effect as biomarker or in clinical decision making on an individual level due to large intraindividual variability.

KEYWORDS:

Conditioned pain modulation; Experimental pain; Reliability

Conflict of interest statement

Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article.

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