A closed-loop system for maintaining constant experimental muscle pain in man

Abstract

Reliable experimental models are needed to help improve our knowledge of how the central nervous system adapts to function in the presence of muscle pain in man. We developed a microprocessor-based control system for maintaining a constant level of experimental muscle pain. Pain was induced in the relaxed right masseter of healthy young adults by using an infusion pump to inject an algesic 0.15 mL bolus of 5% hypertonic saline over 15 s. Subjects supplied feedback on their present pain intensity (PPI) via a 10 cm long electronic visual-analog scale (VAS) and a 0.07 Hz zero-order hold. The adaptive controller identified the system dynamic response and proportional-integral-derivative (PID) controller parameters from the subject's initial response to the bolus (pain rise and fall time constants and peak amplitude) as well as his/her response to a 90 s constant infusion. Finally, using the pain feedback the adaptive PID controller was successfully used to adjust the infusion rate to maintain PPI in five out of seven healthy adults at a mean (SD) 4.8(0.9) PPI level with respect to the 5.0 PPI setpoint for periods up to 15 min (when the experiment was arbitrarily terminated). The infusion rate required to maintain the given level of masseter pain was found to increase by approximately 3 to 5%/minute.

Placebo Effects Mediated by Endogenous Opioid Activity on μ-Opioid Receptors

“…Deep sustained muscle pain was maintained from 40 to 60 min after radiotracer administration by the infusion of medication-grade 5% hypertonic saline into the relaxed masseter (jaw) muscle via a computer-controlled pump (total volume, 2.91 Ϯ 0.96 ml), as described previously (Zhang et al, 1993;Stohler and Kowalski, 1999). Briefly, after the standardized bolus injection of 0.15 ml of hypertonic saline, infused over 15 s, subjects were required to report the present pain intensity every 15 s on an electronic version of 100 mm visual analog scale (VAS), with the lower and upper bound of the scale marked with numbers 0 and 100, representing the range from "no pain" to "the most pain intensity imaginable."…”

“…However, sustained pain also induces the activation of antinociceptive responses (Levine et al, 1978;Watkins and Mayer, 1982;Zubieta et al, 2001), which by substantially reducing pain ratings over time (Bencherif et al, 2002) may interfere with the subsequent formation of the placebo effect (Price et al, 1999). These issues were addressed by using an adaptive system that maintained pain over time by increasing the magnitude of the algesic stimulus as the rating of pain intensity reported by the volunteers declined over time (Zhang et al, 1993). The increases in algesic requirement then provided an objective psychophysical measure of antinociceptive activity, whereas the relationship between stimulus magnitude and pain ratings relate it to the subjective individual experiences of pain.…”

Craniofacial Pain and Motor Function: Pathogenesis, Clinical Correlates, and Implications

“…In experimentally induced pain, significantly smaller vertical and lateral movement amplitudes were found in deliberate unilateral chewing in the condition of pain (Svensson et al, 1996). When computer-controlled infusions of hypertonic saline were used to study the effect of pain intensity on jaw motor function (Zhang et al, 1993), the maximum voluntary jaw-opening movements became smaller with increasing pain intensities. In parallel, masseteric motor units fired at higher rates with increasing pain intensities.…”

Variations in the Human Pain Stress Experience Mediated by Ventral and Dorsal Basal Ganglia Dopamine Activity

“…Here pain was maintained from 45 to 65 min after the administration of radiotracer by the infusion of medication-grade 5% hypertonic saline into the relaxed masseter (jaw) muscle via a computercontrolled closed-loop system, as described previously (Zhang et al, 1993;Stohler and Kowalski, 1999). Initially, the subject-specific parameters of the system for maintaining muscle pain are established.…”