The effects of chronic electrical stimulation on laryngeal muscle physiology and histochemistry.

The present study examined the effects of functional neuromuscular stimulation (FNS) on posterior cricoarytenoid (PCA) muscle physiology and histochemistry. In 4 canines, 10 cm of the recurrent laryngeal nerve was resected. A patch electrode array was implanted for PCA stimulation. FNS was applied to 2 canines for a period of 4 weeks with 2 additional animals serving as nonstimulated controls. Results indicated that FNS increased PCA muscle contractility over the period of intervention but had no effect on contraction speed. FNS also protected the muscle from atrophy by preventing muscle weight loss and type 2 fiber deterioration. Finally, it rescued muscle fibers from ensuing fibrosis.

The effects of chronic electrical stimulation on laryngeal muscle reinnervation.

The present study examined the effects of functional neuromuscular stimulation (FNS) on reinnervation of the posterior cricoarytenoid (PCA) muscle. In 4 canines, the recurrent laryngeal nerve (RLN) was sectioned and anastomosed and a patch electrode array implanted for stimulation and recording at multiple PCA sites. Following implantation, FNS was applied to 2 canines for a period of 6 weeks. Two additional animals served as nonstimulated controls. In each animal, histomorphometric analysis of the RLN was used to assess the quality of nerve regeneration and the potential for muscle reconnection. The magnitude of reinnervation was monitored by electromyographic (EMG) potentials evoked by RLN stimulation. The appropriateness of reconnection was determined by the pattern of spontaneous EMG activity and recovery of vocal fold abduction. Results of this preliminary study indicated that FNS caused an overall repression of reinnervation. However, the repression preferentially inhibited reconnection by foreign nerve fibers, promoting selective reinnervation and preventing synkinesis.

Electrical pacing of the paralyzed human larynx.

This study represents the first attempt to electrically pace the paralyzed human larynx. The goal was to determine if electrical stimulation of the posterior cricoarytenoid muscle could produce functional abduction of the vocal fold in pace with inspiration. An external apparatus was used to sense inspiration and reanimate the unilaterally paralyzed larynx of a thyroplasty patient. Stimuli were delivered through a needle electrode to locate and pace the abductor muscle. The magnitude of electrically induced abduction was comparable to spontaneous movement on the normal side. The abduction was appropriately timed with inspiration: this finding demonstrated that this simple pacing system could effectively modulate stimulation with patient respiration.

Intraoperative monitoring of the visual evoked potential during endoscopic sinus surgery.

Iatrogenic blindness resulting from conventional and endoscopic sinus surgery continues to be a major concern to the head and neck surgeon. A new electrophysiologic monitoring technique has been developed that can help avoid damage to the optic nerve and visual system. The approach involves monitoring the visual evoked potential with presentation of flash stimuli to the eyes. Thirty patients with chronic sinusitis underwent endoscopic sinus surgery with visual evoked potential monitoring. The procedures were carried out with patients under intravenous general anesthesia. Needle cortical electrodes were placed in the scalp. A modified light-emitting diode array/goggle was positioned in front of the patient's closed eyes. A triggered flash of 2 Hz was delivered through the goggle to stimulate the patient's retina. Cortical responses were amplified and averaged for 100 trials. Amplitude and peak-latency changes were monitored to alert the surgeon to any change in the visual response during the surgical dissection. Although no changes in response were noted during dissection, cold-water irrigation and reflected telescopic light could produce variations in the recorded responses, as will be discussed. Visual evoked potential monitoring may prevent a surgeon from continuing a bilateral procedure when there is indication of iatrogenic visual loss from dissection on the first side. Visual evoked potential also reassures the operator that no damage has occurred to the visual pathway at the conclusion of a case. Methods, case selection, operative technique, and documentation of monitoring will be discussed.

Technical approach for reanimation of the chronically denervated larynx by means of functional electrical stimulation.

Functional electrical stimulation (FES) of the posterior cricoarytenoid (PCA) muscle to produce vocal fold abduction offers an alternative approach to current surgical therapies for bilateral vocal fold paralysis. The purpose of this study was to characterize the application of FES to chronically denervated PCA muscles. Specific goals were to develop a stimulus delivery system for the PCA muscle, determine a practical means of implantation, and identify stimulus parameters effective in activating chronically denervated muscle. Seventeen dogs were implanted with planar electrode arrays 3 months after unilateral recurrent laryngeal nerve resection. A nail-bed electrode array allowed discrete activation of the PCA muscle and gave the greatest abductions, with minimal charge dissipation. Muscle mapping revealed hot-spot regions on the PCA muscle surface, in which stimulation produced maximum abduction. A conservative stimulus paradigm effective in activating chronically denervated muscle was a 1-second pulse train of 2-millisecond-duration pulses, delivered at a tetanizing frequency of 30 Hz and an amplitude of 4 to 14 mA.

Bacterial allergy in nasal polyposis. A new method for quantifying specific IgE.

OBJECTIVES: To determine (1) if bacteria-specific serum IgE levels can be more effectively measured by first absorbing competing IgG antibodies from serum and (2) if patients with chronic paranasal sinus disease exhibit a high positive prevalence of bacteria-specific serum IgE. DESIGN: A modified radioallergosorbent test method was employed wherein each serum sample was absorbed with recProtein A to remove competing non-IgE antibodies, and purified proteins extracted from 16 individual bacteria were used as potential allergens. PARTICIPANTS: Twenty-four patients with nasal polyposis and 14 with chronic sinusitis, all refractory to conventional medical therapy and requiring endoscopic sinusotomies, were tested. Tested as controls were 10 subjects with chronic allergic rhinitis, without a history of chronic sinus disease, and possessing total serum IgE and inhalant-specific IgE levels equal to or higher than the patient group. RESULTS: (1) Pretreatment of serum samples with recProtein A resulted in an increase of bacteria-specific radioallergosorbent test sensitivity. (2) Seventeen of 24 patients with polyps, eight of 14 with chronic sinusitis, and one of 10 with chronic allergic rhinitis were determined to be IgE positive when tested with this assay. CONCLUSIONS: (1) Bacteria-specific serum IgE can be quantified; (2) most patients with nasal polyposis and/or chronic sinusitis possess bacteria-specific IgE in their serum, while subjects with only allergic rhinitis do not; and (3) multiple bacterial species isolated from chronically infected sinuses are capable of inducing IgE-mediated sensitization.

Effects of denervation on laryngeal muscles: a canine model.

The purpose of this study was to chronologically evaluate the changes in functional and histomorphometry of denervated laryngeal muscles. In 14 adult mongrel dogs, a 2.5-cm segment of the right recurrent laryngeal nerve was excised. Videolaryngoscopy and electromyography were performed at 1, 2, 3, 4, 5, 6, and 9 months under intravenous sedation. The animals were then killed, and the laryngeal muscles were processed for histochemical reactions. The mean muscle fiber diameter, standard deviation, and muscle fiber type composition were determined. The findings indicate that, following recurrent laryngeal nerve sectioning, the canine intrinsic laryngeal muscles undergo denervation atrophy for approximately 3 months, after which reinnervation occurs. The source of reinnervation appears to be from regenerated nerve fibers of the sectioned recurrent laryngeal nerve. The nerve fibers nonselectively reinnervated the abductor and adductor muscles of the larynx.

Facial nerve antidromic recordings in patients with Bell's palsy.

Antidromic facial nerve action potentials have been recorded noninvasively from the tympanic membrane (TM) of patients with Bell's palsy. A standardized approach has been developed in normal subjects that involves differential recording between the TM and adjacent canal wall. A metal annulus on the tip of an ear speculum served as the reference electrode. The speculum was held in place by an adjustable headband. A conductive sponge electrode inserted through the speculum served as the active TM electrode. In clinical trials, nerve potentials recorded from the paralyzed side were abnormal in all patients tested, indicating that nerve pathology could be monitored with this technique. Abnormalities were evident at the first test, within the first day of paralysis for some patients, and well in advance of any abnormality in the electroneuronography (ENoG) response. There appeared to be a relationship between specific waveform abnormalities (e.g., increased peak latency, waveform temporal dispersion, decreased area) and the tendency for a patient to recover from paralysis. These observations suggest that the technique described could serve as a means for early prognosis, at a stage in which nerve damage could still be effectively treated.

Evoked accelerometry: a sensitive and accurate method for evaluating facial nerve function using a portable device.

A new electrodiagnostic technique has been developed which can be used to monitor facial nerve function. The technique has been termed "evoked accelerometry" (EAC) and is administered by a portable DC powered device. In performing a test, the device stimulates the facial nerve and then measures the evoked muscular response by a small accelerometer sensor affixed to the face with suction. The magnitude of the response is displayed as a digital readout on the device meter. The degree to which a reading is subnormal indicates the extent of nerve degeneration. In a study of normal participants the stimulus-response characteristics of the EAC technique were found to be similar to those of ENoG, indicating the clinical efficacy of the technique. However, evoked accelerometry was found to be more sensitive than ENoG (i.e., detectable response of 0.3% to 0.6% vs. 1.8% to 5.2%) and more accurate than ENoG (average error of 6.8% vs. 13.9% to 20.7%).

Complications in the approach to acoustic tumor surgery.

Earlier diagnosis and cooperation with allied specialists in neurosurgery have lessened complications of acoustic tumor surgery. To date, complications cannot always be prevented. The controversy over which approach is best for acoustic tumor extirpation still continues. While teams must answer this question themselves, our experience favors the transtemporal approach. Of the potential disabilities from this operation, facial paralysis or its sequelae remain the most frequent. The transtemporal approach gives a more accurate anatomical definition of the facial nerve. Efforts to preserve hearing (especially with tumors 2 cm or larger), when matched with the potential sequelae of facial paralysis, may prove futile.