This system can be used to manufacture a simple, economical and implantable system for long-term recording of evoked or spontaneous electromyographic potentials. The main advantage of this system over conventional chronic EMG recording systems is the lead wires are coiled and are resistant to breakage or disruption in the awake moving animal. The main application of this technique is to investigate the specificity of the renovation of laryngeal muscles in the presence of electrical conditioning therapy to avoid synkinesis.
This technology can also be applied to other neuromuscular system for which chronic nerve stimulation and/or EMG recording in awake moving animals is needed. Introducing the procedure will be Shan Huang, a research assistant professor of otolaryngology in my lab. Before preparing an RLN stimulus electrode cuff, cut 170 centimeter length of Teflon-coated multi-filament type 316 stainless steel wire for each cuff and use a coiling device to coil the wires into 12 centimeter long springs.
If necessary, stretch the spring to increase its length for each implant site. Leave three millimeters of one end and 10 millimeters of the other end of each coiled lead straight and de-insulate each end. Then solder a gold-plated copper female pin into the three millimeter end of each coiled lead.
To prepare the nerve cuff, cut a five millimeter segment of silicon tube from a roll of tubing. Under the operation microscope, use a 25 gauge hypodermic needle to pierce through the tubing wall 1.5 millimeter from the end and off center close to the inner wall. Backfill the 10 millimeter end of one lead into the tip of the needle and withdraw the needle to deposit the de-insulated portion into the tube.
Bend back the bare wire end outside of the tube and twist the wire onto the lead at its point of entry into the tube to anchor the lead to the tube. In order to insert the second lead 1.5 millimeters from the opposite end of the tube, align the point of entry to that of the first lead. Use the needle to pierce the wall and slide its shaft near the inner wall opposite to the first lead.
Backfill the needle with the de-insulated 10 millimeters end and remove the needle. The two stimulus electrodes should form a 45 degree V-shape that will straddle the nerve to ensure current delivery through the nerve from the anode to the cathode. Use a pair of curved scissors to make an S-shaped slit in the tube wall opposite the electrode points of entry and use a curved microsurgical needle to insert a length of 6-0 monofilament nonabsorbable suture into the cuff wall at each end.
Combine a blob of medical-grade type A silicone gel with its solvent in an Eppendorf tube and mix on a vortex mixer. Apply the gel prep using a 30 unit insulin syringe to re-insulate all of the exposed bare wire outside of the cuff. To prepare an SLN stimulus electrode cuff, assemble the cuff as just demonstrated using a smaller diameter tube.
To prepare a PCA EMG recording electrode, assemble a coiled lead for the PCA muscle electrode and solder a female pin onto three millimeter end of the lead as demonstrated. Use a 25 gauge needle to insert the 10 millimeter end of the PCA muscle lead into the tip of a deep brain stimulation electrode and bend the end of the lead to form a hook. Then clip the lead to provide a total of five millimeters of recording length.
To prepare a skin receptacle for interfacing the connections between the electrodes and the external equipment, cut two 17.5 millimeter pieces each containing eight pinholes from a single row female pin strip connector and use sandpaper to roughen the external surfaces of each piece. Use phenol to glue the sanded pieces together in a fume hood and place the resulting double-row connector in a container of 60-80 degree water in the fume hood for 30 minutes. While the glue is hardening, cut a 25.6 millimeter faceplate from the strip.
Drill a hole in the middle of the faceplate. Enlarge the hole with a drill press and scalpel to make a 5.4 by 17.4 millimeter rectangular hole centered in the middle of the faceplate. Finish and square up the corners of the hole with a file.
When the glue has dried, insert the edge of the double-row connector with the larger diameter holes inside the rectangular hole of the faceplate until it is flushed with the faceplate surface. Use phenol to adhere the connector to the faceplate and place the assembly into 60-90 degree water. When the phenol has hardened, drill a 1.3 millimeter hole into each corner of the faceplate and on each side of the faceplate halfway from each end.
Cut a 15 millimeter length tube of knitted polyester graft and use a hypodermic needle to thread stainless steel wires through the wall at three positions 3.8 millimeters apart along the length of the graft to fix the tube to the assembly. Place equally spaced notches in each corner of the connector to anchor the wires against the assembly surface and use pliers to twist the ends of each wire to cinch the tube to the assembly. Then make a permanent mark on the polyester patch at one end of the receptacle.
Make a midline neck incision from the thyroid notch to manubrium. After exposing the inferior border of the cricoid cartilage in an anesthetized canine, position the stimulus cuff onto each of the bilateral SLNs and RLNs and use the enclosed sutures to close the lips of each cuff. Use a biopsy punch to make a four millimeter cartilage window on each side of the anterior surface of the thyroid cartilage and expose the lateral aspects of both the thyroarytenoid lateral cricoarytenoid muscle complexes.
Insert the barb of each EMG recording electrode into the TA LCA complex using a 23 gauge needle and suture the polyester patch onto the cricoid cartilage at each of the four corners. Place the deep brain stimulation electrode with its companion hook wire EMG recording electrode underneath the PCA muscle on each side and use an endoscope to confirm that the stimulation produces a vocal fold abduction for each channel. Use 4-0 nonabsorbable sutures to anchor the deep brain stimulation electrodes to the cricoid cartilage using an anchor that locks onto the lead.
Insert all of the wire leads of the nerve stimulation EMG recording electrodes into the receptacle via their female pins using an insertion tool fashioned from a hemostat. Use bone cement to seal the inferior surface of the receptacle to insulate the lead pin junctions. When the cement has hardened, place the receptacle at the rostral end of the midline incision and suture the receptacle to subcutaneous tissues via the polyester skirt.
Then pass the sutures through the faceplate holes to attach the skin edge to the receptacle. Here, a representative EMG recording from one of the baseline sessions with the RLNs intact is shown. In a recording from the PCA muscle, RLN stimulation produces a stimulus artifact followed by a large evoked EMG potential.
In a recording from the thyroarytenoid lateral cricoarytenoid muscle complex, SLN stimulation produces a stimulus artifact that is followed by a short latency monosynaptic muscle response and a longer latency polysynaptic reflex glottic closure response. In this recording, bursts of spontaneous EMG activity can be recorded from the PCA muscle during normal inspirations. This inspiratory EMG activity increases over the course of carbon dioxide delivery at a slower sweep speed.
There's no inspiratory innervation of the thyroarytenoid lateral cricoarytenoid muscle complex so no inspiratory potentials should be detected from these muscles. This technology has been adapted to investigate the impacts of electrical conditioning on the re-innervation specificity of rabbit facial muscles and also the atrophy of aging rat tongue muscles.
