Multiple session experimental pain measurement

Abstract

Experimental heat pain transients were administered to 30 normal volunteers over four weekly sessions, measuring both heat pain (HP) threshold and suprathreshold magnitude estimation through VAS. Repeatability and bias for these two factors were evaluated. Heat pain thresholds measured through the method of limits were previously shown to have inter-session bias, presumably due to a practice effect. Existence of such a bias between first and second measurement sessions casts doubt on the usefulness of this parameter for pain assessment of individuals over time. In the present study, measurements of normal HP thresholds over four sessions showed that bias exists between the first and successive sessions, but not among sessions other than the first. It is concluded that (i) HP thresholds obtained from a single session are of limited value, and should be carefully interpreted. (ii) Long-term studies that use the HP threshold should take results from the second (or later) session as their baseline. The Visual Analog Scale (VAS) is considered the 'gold standard' for assessment of clinical and suprathreshold experimental pain, and changes in VAS score are regarded as significant evidence of individual response to treatment, placebo, or experimental manipulation. Although its overall group accuracy and precision have been examined for both clinical and experimental pain, and found adequate (Price 1988), the VAS has not been rigorously assessed for repeatability. Stimuli at three pain levels, 1.5, 3 and 4.5 degrees C above each individual's heat pain threshold as determined at each session, were given. Several models of analysis of the VAS were tested and repeatabilities (r) obtained from these analyses demonstrate poor precision for each of the tested analysis models. For example, inter-session repeatabilities for the three individual pain levels ranged from r = 3.8-4.7, effectively providing a confidence interval of 7.6-9.4 for any VAS reading on a 0- to 10-point scale. An examination of intra-session VAS provided somewhat better results. Thus, use of the VAS in similar experimental settings is called into question. The use of the VAS in clinical settings, where individual assessments are necessary, is also called into question, but remains to be specifically tested.

Neuropathic pain: Are there distinct subtypes depending on the aetiology or anatomical lesion?

“…However, they are difficult to use in large samples (18,34,39), despite their significant advantages for pathophysiological studies (3,9,13,18). Additionally, normative values (30) are not relevant to elderly patients, are limited to some pain areas and do not include responses to suprathreshold stimulation, which may be less reliable on repeated examination (38). Our data demonstrate the validity of NPSI-based self-assessment of evoked pains, making it suitable for our study and for clinical practice and therapeutic trials.…”

Across- and within-session variability of ratings of painful contact heat stimuli

“…Previous reports indicate that VAS ratings of painful heat are not highly repeatable measures of pain on an individual subject level (Yarnitsky et al 1996) but exhibit relatively stable mean values for groups of individuals within a single session (Granot et al 2003) and across multiple sessions over a 4-week period (Rosier et al 2002). However, a recent study reported that group ratings of painful heat stimuli declined significantly across an 8-day period, with associated reductions in pain-related brain activity (Bingel et al 2007).…”

Assessing analgesic actions of opioids by experimental pain models in healthy volunteers – an updated review

“…Normally summarized pain measures are more robust giving a high signal to noise ratio, which determines the sensitivity of the pain model [122].The 'method of levels' is a stimulation paradigm where certain levels of stimulus intensities are presented to the subject in preferentially random order and the subject then scores the level of pain. The 'method of limits' is a stimulation paradigm where the level of stimulus intensity is gradually increased until, for example, the pain detection threshold is reached.This method often gives a higher variability than the 'method of levels' probably because reaction time is an important factor in the 'method of limits' [123].…”