FNI

Phrenic Nerve Recording for Breath Synchronization

Principal Investigator: Dustin Tyler, Ph.D.

Staff/Students : Nameth Syed Shah

Funding Sources : NIH/NIDCD

Description: The purpose of the research projects is the development of an implantable laryngeal pacemaker to achieve reanimation of the vocal fold adductor muscles for restoration of normal ventilation in patients with bilateral vocal fold paralysis. This involves the determination of a suitable physiological signal for triggering and controlling the laryngeal pacing; the development of a  system for detection of this ‘controller’ physiological signal, which includes the filters, pre-amplifiers and electrodes; development of a system for the stimulation and determination of the ideal stimulation site for stimulating the adductor muscles; adaptation of this technology for human implants and finally, compare the performance of the laryngeal pacing treatment with other methods of treatment like tracheotomy and cordotomy. This project involves initial experiments with the canine model with the intention of eventually employing and testing in human subjects.

Bilateral vocal fold paralysis (BVFP) results from injury to the recurrent laryngeal nerve and results in a paramedical position of the vocal folds. The paramedical position of the vocal folds obstructs airflow and limits an individual’s respiration. Consequently, patients with BVFP often become extremely fatigued with even simple exertion, such as walking up a flight of stairs. Others have previously shown that direct or indirect electrical stimulation of the posterior cricoarytenoid muscles in an open loop system improve subject respiration (Zealear, Billante et al. 2002; Zealear, Rodriguez et al. 2002; Broniatowski, Grundfest-Broniatowski et al. 1989). To develop a closed loop, demand driven system, we have explored the use of Flat Nerve Interface Electrodes (FINEs) for recording respiratory drive from the phrenic nerve.  The challenge of nerve recording is to record spontaneous nerve activity in freely moving animals. The nerve signal is typically only a few mV in magnitude and swamped by surrounding muscle activity (EMG) and other electromagnetic interference. We have investigated the use of FINEs to is to reshape the nerve for better nerve recordings by virtue of the closer proximity of the sensing electrode contacts to the nerve fascicle (Figure 1). We have shown that the FINE can record phrenic nerve activity correlated with respiration (Figure 2), even in the presence of surrounding EMG activity.

Clinical Significance: Bilateral laryngeal paralysis is a serious and often life-threatening clinical condition. Damage to the recurrent laryngeal nerve, compromises both the adduction and abduction function and the vocal folds are arrested in a near closed position. In such conditions, laryngeal surgery is usually recommended to enlarge the airway and restore breathing from the mouth. This approach may damage voice quality and compromise airway protection during swallowing. This research project is aimed at building innovative instrumentation and methodology that will deliver independent bilateral stimulation of the abductor muscles in synchrony with inspiration, without compromise of deglutition or voice. It is aimed that with the aid of this technology, the patient should be able to return to normal, active lifestyle.

References:

• Broniatowski, M., S. Grundfest-Broniatowski, et al. (1989). "Excitation thresholds for nerve pedicles: a preliminary report." Otolaryngol Head Neck Surg 100(6): 578-82.
• Zealear, D. L., C. R. Billante, et al. (2002). "Electrically stimulated glottal opening combined with adductor muscle botox blockade restores both ventilation and voice in a patient with bilateral laryngeal paralysis." Ann Otol Rhinol Laryngol 111(6): 500-6.
• Zealear, D. L., R. J. Rodriguez, et al. (2002). "Electrical stimulation of a denervated muscle promotes selective reinnervation by native over foreign motoneurons." J Neurophysiol 87(4): 2195-9.