Computational Parametric Analysis of the Mechanical Response of Structurally Varying Pacinian Corpuscles.

The Pacinian corpuscle (PC) is a cutaneous mechanoreceptor that senses low-amplitude, high-frequency vibrations. The PC contains a nerve fiber surrounded by alternating layers of solid lamellae and interlamellar fluid, and this structure is hypothesized to contribute to the PC's role as a band-pass filter for vibrations. In this study, we sought to evaluate the relationship between the PC's material and geometric parameters and its response to vibration. We used a spherical finite element mechanical model based on shell theory and lubrication theory to model the PC's outer core. Specifically, we analyzed the effect of the following structural properties on the PC's frequency sensitivity: lamellar modulus (E), lamellar thickness (h), fluid viscosity (µ), PC outer radius (Ro), and number of lamellae (N). The frequency of peak strain amplification (henceforth "peak frequency") and frequency range over which strain amplification occurred (henceforth "bandwidth") increased with lamellar modulus or lamellar thickness and decreased with an increase in fluid viscosity or radius. All five structural parameters were combined into expressions for the relationship between the parameters and peak frequency, ωpeak=1.605×10-6N3.475(Eh/µRo), or bandwidth, B=1.747×10-6N3.951(Eh/µRo). Although further work is needed to understand how mechanical variability contributes to functional variability in PCs and how factors such as PC eccentricity also affect PC behavior, this study provides two simple expressions that can be used to predict the impact of structural or material changes with aging or disease on the frequency response of the PC.

Comparison of NSAID patch given as monotherapy and NSAID patch in combination with transcutaneous electric nerve stimulation, a heating pad, or topical capsaicin in the treatment of patients with myofascial pain syndrome of the upper trapezius: a pilot study.

OBJECTIVE: This study compared the therapeutic effect of monotherapy with a nonsteroidal anti-inflammatory drug (NSAID) patch vs an NSAID patch combined with transcutaneous electric nerve stimulation (TENS), a heating pad, or topical capsaicin in the treatment of patients with myofascial pain syndrome (MPS) of the upper trapezius. DESIGN: A randomized, single-blind, controlled study of combination therapy for patients with MPS was performed. METHODS: Ninety-nine patients were randomly assigned to one of four different self-management methods for treatment: NSAID patch (N = 25), NSAID patch + TENS (N = 24), NSAID patch + heating pad (N = 25), and NSAID patch + topical capsaicin (N = 25). The NSAID patch used in this study was a ketoprofen patch. All treatment groups were observed for 2 weeks, and the numeric rating scale (NRS) pain score, cervical active range of motion, pressure pain threshold, and Neck Disability Index were assessed. RESULTS: There was no significant difference between the NSAID patch alone group and the three combination therapy groups with respect to decrease in NRS score from baseline (day 0) to each period of observation. In covariate analysis, although there was no difference among the groups in most of the periods, the data at day 14 indicated a trend (P = 0.057). There were no significant differences in the other variables. CONCLUSIONS: We did not observe a statistical difference in improvements to the clinical variables among the four different methods. However, further studies regarding the effectiveness of a mixture of topical capsaicin and ketoprofen in patients with MPS should be considered.

Ovoid geometry of the Pacinian corpuscle is not the determining factor for mechanical excitation.

Static displacements in Pacinian corpuscles (PCs) were measured using video microscopy. Mechanical stimuli of 10-40 microm steps were applied to the PC capsule surfaces using cylindrical contacts with different diameters. Displacements parallel to the stimulation axis were measured at various locations in the focal plane of the optical setup. In contrast to previous data in the literature, the displacements within the corpuscle were found to be linearly related to the indentation amplitude. Displacements decreased as a function of lamella depth, with a more negative slope close to the surface and less negative slope at deeper locations. The experimental data were compared to the predictions of a previous mechanical model, and to the results of two new models: (1) elastic semi-infinite continuum model; (2) ovoid isotropic finite-element model. Although the previous model did not specify displacement boundary conditions, it predicted the current experimental results well. On the other hand, the experimental displacements were found to be smaller than those predicted by the semi-infinite continuum and finite-element models. However, both semi-infinite continuum and finite-element models yielded close results, which show that the three-dimensional ovoid geometry of the corpuscle is not the primary factor for determining the displacements in physiological conditions. Furthermore, simulations with the finite-element model using a wide range of material properties yielded similar results. This supports the hypothesis that a homogeneous isotropic model for the PC cannot predict experimental results. The modeling analyses suggest that the experimental results are largely affected by the displacement of the incompressible interlamellar fluid and the layered structure of the corpuscle.