Relative Sensitivity to Alfentanil and Reliability of Current Perception Threshold Vs Von Frey Tactile Stimulation and Thermal Sensory Testing

Recent technological advances claim to allow quantitative measurement of the functional integrity of both large and small diameter sensory nerve fibers using the current perception threshold (CPT) sensory testing device. This device has yet to be validated against the corresponding gold standard references for sensory testing (thermal sensory testing [TST]) and von Frey tactile hair stimulation [VF]) to correlate its evaluation of similar sensory nerve perceptions. A baseline neurosensory examination using the CPT, TST and VF methods was performed on 19 healthy volunteers. Using a randomized, double-blind, placebo-controlled design, each subject received an alfentanil or diphenhydramine (as a placebo control) infusion in separate study sessions. The order of the study sessions was randomized and separated by 1 week. The 3 neurosensory examinations were repeated at 3 different targeted plasma levels of study drug. Changes in neurosensory thresholds were then compared between the 3 methods. All CPT measurements and the cold pain measurement showed a significantly higher degree of variability than the other TST and VF measurements. There appeared to be a correlation between the CPT 5 Hz pain threshold and the TST cold pain and warm sensation; intravenous alfentanil significantly elevated all 3 detection thresholds. In addition, there was no effect of alfentanil on the VF or the CPT 2000 Hz thresholds. However, we did not see the predicted relation between the 250 Hz CPT stimulus and cool sensation. From these studies, there is some evidence that similar fiber tracts may be measured between the CPT, TST, and VF methods, especially with the CPT 5 Hz measures and C-fiber tract activity.