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Published on: January 14, 2009
Internal validity of inter-digital web pinching as a model for perceptual diffuse noxious inhibitory controls-induced
Anouk Streff1, Gilles Michaux, Fernand Anton
1Laboratory of Psychophysiology, University of Luxembourg, Luxembourg.
Insights
Inter-digital web pinching (IWP) effectively triggers diffuse noxious inhibitory controls (DNIC) for pain modulation. This method is less confounded by baroreflex sensitivity (BRS) than hot water immersion (HIT), offering a clearer understanding of endogenous pain control mechanisms.
Area of Science:
- Neuroscience
- Pain Research
- Human Physiology
Background:
- Heterotopic noxious counter-stimulation (HNCS) using hot and ice-water immersions are common for studying endogenous pain modulation.
- Thermoregulatory activity during HNCS complicates differentiating between baroreflex sensitivity (BRS) and diffuse noxious inhibitory controls (DNIC) related hypoalgesia.
Purpose of the Study:
- To analyze the internal validity of inter-digital web pinching (IWP) as a tonic pain model for inducing DNIC.
- To differentiate between BRS-related and DNIC-like hypoalgesia by comparing IWP with hot water immersion (HIT).
Main Methods:
- A randomized controlled study involving 24 healthy volunteers assessed mechanical and thermal perceptual wind-up before and after IWP (15N) or HIT (47.5°C) for 2 minutes.
- Wind-up was induced by repetitive heat or ballistic impact stimuli. Cardiovascular activity, pain experience, and corrugator muscle activity were monitored.
Main Results:
- Both HNCS methods induced similar pain experiences, but HIT showed more pronounced cardiovascular activity, indicating BRS contamination.
- Wind-up was significantly reduced by both HNCS types, with a stronger effect for HIT than IWP.
- IWP demonstrated validity for DNIC induction with minimal BRS confounding.
Conclusions:
- HNCS methods allow differentiation between BRS-related and DNIC-like hypoalgesia.
- Inter-digital web pinching (IWP) is a valid and less confounded model for inducing DNIC, crucial for understanding endogenous pain modulation.
Abstract:
Hot and ice-water immersions are commonly used for heterotopic noxious counter-stimulation (HNCS) in investigations on endogenous pain modulation. However, coincident sympathetic thermoregulatory activity does not allow to differentiate between perceptual hypoalgesia related to baroreflex sensitivity (BRS) or diffuse noxious inhibitory controls (DNIC). The present study analysed the internal validity of another supposedly less confounded tonic pain model (inter-digital web pinching; IWP) regarding its potential as DNIC trigger. We performed a randomized controlled study in 24 healthy gender-matched drug-free volunteers aged 21-54 (median 25) years. The study protocol comprised the assessment of mechanical and thermal perceptual wind-up before and after an IWP (15N) or hot water immersion trial (HIT; 47.5°C) of 2 min duration. Wind-up was induced either by 10 repetitive (1Hz) contact heat (max. 49°C; 5×5 mm thermode) or ballistic impact stimuli (0.5g at 9 m/s) on the phalanges of the non-dominant hand. Cardiovascular activity, pain experience and corrugator muscle activity were continuously monitored. Although both HNCS forms produced a similar pain experience (45% of scale), a more pronounced cardiovascular activity was observable for the HIT (P<0.01). This indicates a higher baroreceptor activity and stronger contamination of painful water immersion by BRS-related hypoalgesia. Regardless of pain modality, wind-up was significantly reduced by HNCS, although this was stronger for painful water immersion than for noxious pinching (P<0.01). The HNCS types allow a differentiation between BRS-related and DNIC-like hypoalgesia. IWP proved its validity for DNIC induction, being practically non-confounded by BRS.
