8th World Congress on Pain, Vancouver. Abstracts page 332(5), International Association for the Study of Pain Press, Seattle, 1996.
Evaluation of a New Experimental Electrical Pain Model in Humans
L.R. Poree, M.S. Angst, J.B. Dyck, Department of Anesthesia,
Stanford University, Stanford, CA
Aim of Investigation
"Previous experimental electrical pain models most often utilized a 100 Hz, constant current, square wave stimulus. Subjective criticism of this is that the perception of this stimulus does not "feel" like true pain. A 5 Hz, constant current, sine wave stimulus was examined for its potential to cause a realistic and consistent painful perception in volunteers for pain threshold and pain tolerance values."
Methods
"10 healthy volunteers were tested on two separate days (3 day interval) during a morning and an afternoon session (4 h interval). A stimulating gold surface electrode (0.7 cm²) was attached in a standardized manner over the lateral upper left arm. A constant current device(Neurometer®, Neurotron Inc., Maryland) delivered 5 Hz sine wave electrical stimuli of 3 s duration with an inter-stimulus interval of 15 s. The pain threshold was determined with two different algorithms, a staircase method (stimulus repetitively increases stepwise until painful, then decreases until not painful; threshold results from averaging adjacent values) and a bisection method (derative determination and rating of mid-range intensity between lowest painful and highest not painful stimulus defines threshold value). Pain tolerance was determined by an ascending staircase algorithm only. Results are expressed as median. Statistical analysis was performed with the Mann-Whitney and the Wilcoxin paired-sample test."
Results
"Pain threshold values (mA) were not different for the two algorithms. Pain threshold and pain tolerance were lower in afternoon than in morning sessions (p<0.05). Individual within-day variability was lower for pain tolerance than for pain threshold (p<0.01). Intra-individual within-day variability for pain threshold was 30%. Between-days variability was 37%. Intra-individual within day variability for pain tolerance was 16%. Between-days variability was 26%."
Conclusion
"Noxious 5 Hz, constant current, sine wave stimuli were easy identified by volunteers as realistic painful perception. Pain threshold values were similar with two different stimulation algorithms. Diurnal variation for pain threshold and tolerance were found. The intra-individual variability for pain threshold and tolerance is within acceptable limits for a psychophysical measurement. The 5 Hz, constant current, sine wave stimulus may be a viable alternative to the traditionally used 100 Hz, constant current, square wave stimulus."
