The Miniature Pig: A Large Animal Model for Cochlear Implant Research

Cochlear implantation surgery in mini piggers can be utilized to provide intentional evidence of the safety and potential performance of novel electrode areas and the surgical approach in a living system similar to human beings. Mini piggers are an endo lab animal model for research into cochlear implants. Cochlear implants on mini piggers provide an individual platforms for transplant people with severe to profound sensory neuro hearing loss.

Moreover, it also provides a surgery loss of gene therapy for hearing loss in big animal model. As they are significant and similar, in morphology and structure of osculatory organs between mini piggers and human beings. This surgery method clarifies the procedure and is helpful for beginners.

Demonstrating the procedure will be Ji Xiaojun and Otolaryngology professor and Luo Yi a chief physician from my laboratory. After anesthetizing two months old male pig, monitor the oxygen saturation breathing and heart rate using the pulse oximetry clamp of an ECG monitor connected to the pig's tongue. Place the mini pig in the left lateral position.

Keep the eyes closed using a medical patch to prevent dryness. Shave the 10 centimeter surgical area around the ear lobe. Disinfect the skin with three alternating swabs of iodine and alcohol.

Then cover the surgical area with sterile surgical drapes. Cover the microscope with a sterile plastic sleeve and remove the parts covering the eye pieces and objective. Locate the surface projection site of the cochlea one centimeter behind the posterior auricular sulcus at the level of the ear lobe.

Then, using a scalpel, make a 5 centimeter long postauricular incision with the projection site as the center. Divide the subcutaneous tissue, parotid gland and sternocleidomastoid muscle with micro scissors to expose the surface of the mastoid bone. For cortical mastoidectomy, drill the mastoid at the surface projection of the cochlea on the mastoid bone to the external auditory canal or EAC which is dense and pale blue.

Be careful not to damage the pale or reddish vertical segment of the facial nerve dorsal to the EAC to avoid bleeding. Next, expose the tympanum by drilling the bone surrounding the posterior bony EAC. Separate the skin of the EAC and the facial nerve with a hypodermic needle to avoid damaging the facial nerve.

Carefully push the skin of the EAC away to expose the tympanum including the ossicular chain and round window niche. Then, remove the round window niche with a small diamond bur and keep continuous suction irrigation to expose the basal turn of the cochlea and round window membrane. Separate the cranial parietal muscle to form a pocket for the receiver.

Place the internal receiver package in the muscular pocket and fix it with a fixation suture. Next, insert the electrode array connected to a receiver fixed in a muscular pocket by opening the round window membrane with a sharp microsurgical knife and inserting the array using micro forceps slowly, steadily and continuously in relationship to the modiolus of the cochlea. For evoked compound action potential or ECAP measurements, magnetically connect to the cochlear implant or CI coil to the CI receiver through the skin.

Then using Maestro software, confirm the integrity of the CI and check the electrode impedance for all channels before ECAP measurements using the telemetry function of the CI.To conduct ECAP measurement, select the ECAP module. Then, stimulate all 12 electrodes for ECAP measurements using biphasic stimuli of 30 microseconds phase duration with an alternating polarity paradigm averaging over 25 iterations in a stimulation rate of 45.1 pulses per second. The integrity and impedances of the CI were confirmed by Maestro software.

ECAP results demonstrated that all 12 electrodes showed good neural responses indicating that the electrode array was well attached to the cochlear axis and stimulated the auditory nerve. The post-operative three-dimensional reconstructed electrode coils in the right cochlea are shown. The electrode array was coiled in the basal turn of the cochlea in the electrodes were rendered in green.

Further, three-dimensional reconstruction demonstrates that the electrode array was spirally coiled in the cochlea. The most important thing is to expose the vessel tint of the cochlear and run window member and inside the electrode airways in the protocol. After ace development is technically pales away for combined gene therapy and cochlear implants to treat profound sensor neuro hearing loss in human beings.