School of Medicine and Health Sciences Poster Presentations
Developing a Method to Objectively Assess Sensory Nerve Fiber Sensitivity: A Pilot Study
Document Type
Poster
Abstract Category
Clinical Specialties
Keywords
Pupillary reflex, pupillometry, pain, neurostimulation
Publication Date
Spring 5-1-2019
Abstract
The rate of chronic pain in the United States is greater than the combined rates of diabetes, heart disease, and cancer, with associated healthcare costs ranging from $560-$635 billion per year. It is imperative that an objective assessment tool be developed to ensure adequate pain evaluation and appropriate analgesic intervention is provided to patients experiencing chronic pain. Pupillary reflex dilation (PRD) occurs when an alerting stimulus activates peripheral nociceptive fibers and elicits pupillary dilation. Preliminary data indicates that a unique PRD (nPRD) can be produced by depolarizing sensory nerves fibers via non-noxious neurospecific electrical stimuli at particular frequencies. The area under the curve (AUC) of the nPRD reflects nerve fiber sensitivity and the amplitude correlates with pain self-report. These findings suggest that the nPRD has potential utility in the objective assessment of pain characteristics. In this pilot study of healthy adult subjects, infrared pupillometry was used to evaluate whether the nPRD was reflective of known differences in nerve fiber physiology under tourniquet-induced ischemic conditions. At a baseline state, activated, myelinated Aβ touch fibers inhibit the transmission of presynaptic pain signals by unmyelinated, nociceptive C-fibers to diminish pain sensation. In an ischemic environment, Aβ fibers are not activated and thus no suppression of C-fiber transmission occurs. We hypothesized this phenomenon could be quantified by the nPRD AUC. Baseline nPRD measurements for each fiber type were assessed using perception intensity at a specific activating stimulation frequency (C fiber at 5 Hz, Aδ at 250 Hz, and Aβ at 2000 Hz). A tourniquet was placed on the subject's upper arm and nPRD measurements were repeated at 5-minute intervals. The tourniquet was removed at 20 minutes and final measurements were taken during reperfusion. Five subjects demonstrated the hypothesized outcome. At 12 minutes after tourniquet placement, the Aβ nPRD AUC was diminished while the C-fiber nPRD AUC was significantly increased from baseline. This suggests that ischemia resulted in removal of Aβ regulation and disinhibition of the C-fiber. During reperfusion, the C-fiber nPRD AUC decreased towards baseline indicating a return of Aβ suppression and the Aβ nPRD AUC increased to reflect heightened sensitivity. For all five subjects, there was a significant difference between the Aβ nPRD AUC values (p=0.024) and a difference trending towards significance between the C-fiber nPRD AUC values (p=0.091) at the three time points. These results indicate that the nPRD method is able to detect modulation of nerve fiber sensitivity.
Open Access
1
Developing a Method to Objectively Assess Sensory Nerve Fiber Sensitivity: A Pilot Study
The rate of chronic pain in the United States is greater than the combined rates of diabetes, heart disease, and cancer, with associated healthcare costs ranging from $560-$635 billion per year. It is imperative that an objective assessment tool be developed to ensure adequate pain evaluation and appropriate analgesic intervention is provided to patients experiencing chronic pain. Pupillary reflex dilation (PRD) occurs when an alerting stimulus activates peripheral nociceptive fibers and elicits pupillary dilation. Preliminary data indicates that a unique PRD (nPRD) can be produced by depolarizing sensory nerves fibers via non-noxious neurospecific electrical stimuli at particular frequencies. The area under the curve (AUC) of the nPRD reflects nerve fiber sensitivity and the amplitude correlates with pain self-report. These findings suggest that the nPRD has potential utility in the objective assessment of pain characteristics. In this pilot study of healthy adult subjects, infrared pupillometry was used to evaluate whether the nPRD was reflective of known differences in nerve fiber physiology under tourniquet-induced ischemic conditions. At a baseline state, activated, myelinated Aβ touch fibers inhibit the transmission of presynaptic pain signals by unmyelinated, nociceptive C-fibers to diminish pain sensation. In an ischemic environment, Aβ fibers are not activated and thus no suppression of C-fiber transmission occurs. We hypothesized this phenomenon could be quantified by the nPRD AUC. Baseline nPRD measurements for each fiber type were assessed using perception intensity at a specific activating stimulation frequency (C fiber at 5 Hz, Aδ at 250 Hz, and Aβ at 2000 Hz). A tourniquet was placed on the subject's upper arm and nPRD measurements were repeated at 5-minute intervals. The tourniquet was removed at 20 minutes and final measurements were taken during reperfusion. Five subjects demonstrated the hypothesized outcome. At 12 minutes after tourniquet placement, the Aβ nPRD AUC was diminished while the C-fiber nPRD AUC was significantly increased from baseline. This suggests that ischemia resulted in removal of Aβ regulation and disinhibition of the C-fiber. During reperfusion, the C-fiber nPRD AUC decreased towards baseline indicating a return of Aβ suppression and the Aβ nPRD AUC increased to reflect heightened sensitivity. For all five subjects, there was a significant difference between the Aβ nPRD AUC values (p=0.024) and a difference trending towards significance between the C-fiber nPRD AUC values (p=0.091) at the three time points. These results indicate that the nPRD method is able to detect modulation of nerve fiber sensitivity.
Comments
Presented at Research Days 2019.