Background & Aims
Background: Conditioned pain modulation (CPM) assesses diffuse noxious inhibitory control (DNIC), an endogenous pain regulatory processes where one pain stimulus reduces the perception of another.1,2,3,4,5 CPM is less effective in chronic pain conditions, and weakened pain inhibition predicts chronic pain4.
Repetitive painful stimulus elicits a reduction in both pain perception and associated responses6. Studies employing experimental pain models characterized by recurrent thermal stimuli have reported diminished subjective pain intensity7. This likely occurs due to frequent activation of the pain-inhibiting system through repeated exposure to painful stimulus. Therefore, repeated engagement of CPM may alter pain processing, leading to improved pain inhibition and enhanced pain relief.
AIM: To determine the extent to which repeated exposure to CPM protocols modifies CPM efficiency.
Methods
Sixty healthy participants [male (48.3%), female (51.7%); aged 18 – 75 years] were randomly assigned to one of three groups: High Exposure (HE – four sessions using CPM as an intervention, five sessions), Low Exposure (LE – one CPM intervention, two sessions), and No Exposure (NE – no CPM intervention, two sessions). Participants performed CPM using cold water as a conditioning stimulus as the intervention. Assessment of CPM efficiency occurred via induction of CPM using heat as a conditioning stimulus. The change in CPM efficiency between sessions, the CPM efficiency value recorded during the fifth visit was subtracted from that observed during the initial visit for each study intervention arm. ANOVA was conducted to examine changes in CPM efficiency in between and within the sessions.
Results
ANOVA results showed no significant differences for changes in CPM efficiency between sessions (Visit 1 and Visit 5), the based on HE and LE intervention, F(1,38) = 0.04; p=0.36; ?2 = 0.02. Within-session changes in CPM Efficiency from pre to post-intervention at Visit 1 also did not significantly differ between the HE and LE groups per the ANOVA, F(1,38) = 0.24; p=0.05; ?2 = 0.09. Exploratory analysis using paired T-test to examine the change in CPM efficiency within the HE and LE arms. This analysis indicated that CPM efficiency for the HE arm was significantly higher after intervention (M=1.29, SD=0.72) than the preintervention (M=0.42, SD= 0.76), (t[19] = -4.21, p < 0.001). Similarly, the CPM efficiency for the LE arm was significantly higher after intervention (M=0.83, SD=0.47) than the preintervention (M=0.21, SD= 0.66), (t[19] = -3.27, p =0.004). The effect size for HE arm was -0.98 (95%CI -1.46 to -0.40) while the effect size for the LE arm was 0.73 (95%CI -1.22 to -0.22).
Conclusions
Both the HE and LE protocols led to enhancements in CPM efficacy. Importantly, the frequency of intervention administration, i.e. HE (4 sessions) and LE (1 session) groups, did not differentially impact on CPM efficiency. These findings suggest repeated exposure to CPM positively changes endogenous inhibition efficiency. Testing in people with pain conditions is needed to determine the impact on clinical pain.
References
1.Pud, D., Granovsky, Y., & Yarnitsky, D. (2009). The methodology of experimentally induced diffuse noxious inhibitory control (DNIC)-like effect in humans. In Pain (Vol. 144, Issues 1–2, pp. 16–19). https://doi.org/10.1016/j.pain.2009.02.015
2.Yarnitsky, D. (2010). Conditioned pain modulation (the diffuse noxious inhibitory control-like effect): Its relevance for acute and chronic pain states. In Current Opinion in Anaesthesiology (Vol. 23, Issue 5, pp. 611–615). https://doi.org/10.1097/ACO.0b013e32833c348b
3.Nir, R. R., & Yarnitsky, D. (2015). Conditioned pain modulation. In Current Opinion in Supportive and Palliative Care (Vol. 9, Issue 2, pp. 131–137). Lippincott Williams and Wilkins. https://doi.org/10.1097/SPC.0000000000000126
4.Granovsky, Y., Nahman-Averbuch, H., Khamaisi, M., & Granot, M. (2017). Efficient conditioned pain modulation despite pain persistence in painful diabetic neuropathy. Pain Reports, 2(3). https://doi.org/10.1097/PR9.0000000000000592
5.Cruz-Almeida, Y., & Fillingim, R. B. (2014). Can quantitative sensory testing move us closer to mechanism-based pain management? In Pain Medicine (United States) (Vol. 15, Issue 1, pp. 61–72). Blackwell Publishing Inc. https://doi.org/10.1111/pme.12230
6.Bingel, U., Schoell, E., Herken, W., Büchel, C., & May, A. (2007). Habituation to painful stimulation involves the antinociceptive system. Pain, 131(1–2), 21–30. https://doi.org/10.1016/j.pain.2006.12.005
7.Savitha, D., Anto, T., & Thomas, T. (2022). Effects of repeated exposures to experimental cold pain stimulus on pain perception in healthy young Indian men. Medical Journal Armed Forces India, 78, S238–S245. https://doi.org/10.1016/j.mjafi.2021.08.002
Presenting Author
Mark Bishop
Poster Authors
Topics
- Mechanisms: Biological-Systems (Physiology/Anatomy)