eCAP (evoked compound action potential) Data
note: early data, updates to come
Testing the Injectrode's Neural Impact
Using the Injectrode, we stimulated sensory nerve fibers. These signals, traveling from the stimulation point to the brain via the spinal column, showcase the Injectrode's ability to modify pain processing—mirroring the effects observed with Spinal Cord Stimulation (SCS) and Dorsal Root Ganglion (DRG) stimulation, offering a modern approach to managing pain in line with the foundational Gate Control Theory.
One stimulation location, several spinal levels being stimulated
By placing an Injectrode either (a) in the PNS pre-ganglionic near the DRG or (b) between the DRG and the spinal column, we are able to engage several spinal levels at once that have nerve rootlets merging to spinal roots.
Transforaminal Injection System Using the Injectrode
The system for transforaminal electrode injection with the Injectrode. The Injectrode can be positioned pre-ganglionic (shown on the right of L5) or post-ganglionic (left of L5) to the DRG. During placement, blunt trocar stimulation helps verify the Injectrode's location. eCAP data can be gathered using a four-contact cylindrical lead on the spinal column. It's noted that when coupled to the Injectrode, transcutaneous stimulation can introduce artifacts to the eCAP measurements.
Fluoroscopy of Injectrode Placements on Pig Left at Right L5 DRG
Fluoroscopy images of the Injectrode placements showing (1) the location of the cranially located cylindrical sensory probe and two Injectrode placement needles being advanced, (2) AP view of Injectrode locations following complete placement with left Injectrode targeting the post-ganglionic roots and the right Injectrode targeting the pre-ganglionic PNS nerves on the edge of the L5 foramen, (3) the lateral view of the L5 left (post-ganglionic) and L5 right (pre-ganglionic) placement.
Comparing percutaneous vs. transcutaneous stimulation results
Typical stimulation thresholds are published by Spinal Cord Stimulation (SCS) and DRG stimulation companies indicating the voltage provided by an implanted pulse generator (IPG) that is directly connected by a wire to the electrodes placed on either the spinal column or on the DRG. The voltages provided by an IPG that are needed to evoke a compound action potential (eCAP) measured more cranially are called "stimulation threshold" and can be used to fine-tune the optimal stimulation for closed-loop control. When the Injectrode is placed either in a pre-ganglionic or a post-ganglionic configuration, and when the tail section that will form the subcutaneous collector is initially left outside the skin intentionally, then a per-cutaneous measurement design allows the capture of similar stimulation thresholds.
Once fully injected, the voltages measured on the outside of the body represent the trans-cutaneous measurement design, meaning the voltages provided by the external pulse generator to evoke CAPs inside the body. Early data allow for an assessment of a transcutaneous vs. percutaneous transfer function.
Percutaneous DRG Stimulation
Nearest-DRG (left), post-ganglionic (middle), and bipolar stim. (L5 left to right lead) during deployment produced eCAP components. Plots show Aꞵ fiber activation. Bipolar stimulation achieved Aꞵ activity at lowest threshold (1V).
Transcutaneous DRG Stimulation
eCAPs for nearest-DRG (left), post-ganglionic (middle), and bipolar stim. (L5 left to right lead) after placement using surface patches (Cadwell 1.25’’, Ambu-Neuro). Aꞵ eCAP components readily discerned at 6-10x perc. thresholds. Post-ganglionic stim. produces more EMG spillover obscuring SEPs.
Interested in a deeper look at our findings? We presented this data about the Injectrode’s capabilities in a detailed scientific poster. Click below and explore the full poster.