Is the introduction of another variable to the strength-duration curve necessary in neurostimulation?

INTRODUCTION: Neurostimulation is the process and technology derived from the application of electricity with different parameters to activate or inhibit nerve pathways. Pulse width (Pw) is the duration of each electrical impulse and, along with amplitude (I), determines the total energy charge of the stimulation. OBJECTIVES: The aim of the study was to test Pw values to find the most adequate pulse widths in rechargeable systems to obtain the largest coverage of the painful area, the most comfortable paresthesia, and the greatest patient satisfaction. MATERIAL AND METHODS: A study of the parameters was performed, varying Pw while maintaining a fixed frequency at 50 Hz. Data on perception threshold (Tp ), discomfort threshold (Td ), and therapeutic threshold (Tt ) were recorded, applying 14 increasing Pw values ranging from 50 µsec to 1000 µsec. Lastly, the behavior of the therapeutic range (TR), the coverage of the painful area, the subjective patient perception of paresthesia, and the degree of patient satisfaction were assessed. RESULTS: The findings after analyzing the different thresholds were as follows: When varying the Pw, the differences obtained at each threshold (Tp , Tt , and Td ) were statistically significant (p < 0.05). The differences among the resulting Tp values and among the resulting Tt values were statistically significant when varying Pw from 50 up to 600 µsec (p < 0.05). For Pw levels 600 µsec and up, no differences were observed in these thresholds. In the case of Td , significant differences existed as Pw increased from 50 to 700 µsec (p ≤ 0.05). The coverage increased in a statistically significant way (p < 0.05) from Pw values of 50 µsec to 300 µsec. Good or very good subjective perception was shown at about Pw 300 µsec. CONCLUSIONS: The patient paresthesia coverage was introduced as an extra variable in the chronaxie-rheobase curve, allowing the adjustment of Pw values for optimal programming. The coverage of the patient against the current chronaxie-rheobase formula will be represented on three axes; an extra axis (z) will appear, multiplying each combination of Pw value and amplitude by the percentage of coverage corresponding to those values. Using this new comparison of chronaxie-rheobase curve vs. coverage, maximum Pw values will be obtained different from those obtained by classic methods.

Effects of movement and postural positions in spinal cord stimulation in the new rechargeable systems.

BACKGROUND: Despite recent developments in implantable neurostimulation devices, the adjustment of stimulation levels to the patient's postural changes has remained a problem so far. OBJECTIVE: This study was conducted with the newest rechargeable devices, in order to compare its results with the ones published from conventional systems. STUDY DESIGN: It is a prospective study. SETTING: In 46 patients implanted with rechargeable constant current stimulation systems we measured impedance, stimulation thresholds, therapeutic range, as well patients' satisfaction and sensation in 7 different body postures. RESULTS: Data analysis was performed in 46 patients, whose most frequent pathologies were failed back surgery syndrome (FBSS) and complex regional pain syndrome (CRPS). The lowest amplitude needed to reach the different thresholds was always scored in the supine decubitus position, with no significant changes in the therapeutic range and impedance. For all stimulation thresholds, there is always a difference between the supine position and all other postures. No statistically significant differences with regard to patients' satisfaction and sensation were found for the different postures. LIMITATIONS: Sample sample size. CONCLUSION: The findings of the present work are similar to those described in previous publications that showed the relationship between postural changes and several stimulation thresholds and pulse energy. The posture which requires lower energy - and whose corresponding therapeutic range (TR) is narrower--is supine decubitus.

Trans-facet-joint approach to pulsed radiofrequency ablation of the L5 dorsal root ganglion in a patient with degenerative spondylosis and scoliosis.

Mechanical low back pain secondary to degenerative facet joint changes is a common reason for referral to pain clinics. When these changes cause encroachment into the intervertebral foramen, radicular pain may result. While pulsed radiofrequency of the dorsal root ganglion can be used in this setting, the anatomic deformity may make the transforaminal approach difficult. We report a case where a trans-facet approach was used successfully and describe the technique.