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Biomedical subjects

D L Zealear

Publications and source records attributed to D L Zealear.

18 recordsLinked to original sources
PubMed1996

Long-term follow-up of recurrent laryngeal nerve avulsion for the treatment of spastic dysphonia.

Long-term follow-up of 3 to 7 years is reported on 18 patients who had undergone recurrent laryngeal nerve avulsion (RLNA) for the treatment of adductor spastic dysphonia (SD). Data on neural regrowth after previous recurrent laryngeal nerve section (RLNS) are presented in 2 of these 18 patients. We introduced RLNA as a modification of standard RLNS to prevent neural regrowth to the hemiparalyzed larynx and subsequent recurrence of SD. We have treated a total of 22 patients with RLNA, and now report a 3- to 7-year follow-up on 18 of these 22 patients. Resolution of symptoms was determined by routine follow-up assessment, perceptual voice analysis, and patient self-assessment. Sixteen of 18, or 89%, had no recurrence of spasms at 3 years after RLNA as determined at routine follow-up. Two of the 16 later developed spasms after medialization laryngoplasty for treatment of weak voice persistent after the avulsion. This yielded a total of 14 of 18, or 78%, who were unanimously judged by four speech pathologists to have no recurrence of SD at the longer follow-up period of 3 to 7 years. Two of these 4 patients were judged by all four analysts to have frequent, short spasms. The other 2 were judged by two of four analysts to have seldom, short spasms. Three of 18 patients presented with recurrent SD after previous RLNS. At the time of subsequent RLNA, each patient had evidence of neural regrowth at the distal nerve stump as demonstrated by intraoperative electromyography and histologic evaluation of the distal nerve stump. One remained free of SD following RLNA, 1 was free of spasms at 4 years after revision avulsion but developed spasms after medialization laryngoplasty, and the final patient developed spasms 3.75 years after revision RLNA. Medialization laryngoplasty with Silastic silicone rubber was performed in 6 of 18, with correction of postoperative breathiness in all 6, but with recurrence of spasm in 3. Spasms resolved in 1 of these with downsizing of the implant. We conclude that RLNA represents a useful treatment in the management of SD in patients not tolerant of botulinum toxin injections.

Adult↗
PubMed1996

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.

Adolescent↗
PubMed1995

An investigation of acute facial paralysis in animals induced by exposure of the tympanic membrane to cold air.

The goal of this investigation was to test the hypothesis that tympanic membrane exposure to cold air is a cause of acute facial palsy. A series of acute invasive experiments and a series of chronic noninvasive experiments were conducted in both cats and dogs. In the acute studies, stimulation was applied intracranially to the facial nerve root through a stereotaxically placed microelectrode and recordings of compound action potentials obtained extracranially from the facial nerve. Nerve conduction was monitored continuously during the application of cold air to the tympanic membrane. Nerve conduction disturbances were observed in all animals tested (8), and reduction in compound action potential amplitude ranged from 33% to 96%. Histologic analysis of the intratemporal portion of the facial nerve was performed in the animal exhibiting the greatest block in conduction, representative of a near-total paralysis. Axon swelling, demyelinization, and degeneration (Bungner's bands) without inflammation were apparent along the entire tympanic membrane segment. Interstitial swelling of nerve endoneurium was also present at the second genu and vertical segment. In the chronic studies, animals were exposed to cold air and monitored daily for facial paralysis after recovery from anesthesia. None of the animals demonstrated any detectable behavioral facial paralysis.

Action Potentials↗
PubMed1995

Reinnervation of the allograft larynx in the rat laryngeal transplant model.

The rat model for a vascularized laryngeal allograft is duplicated with significant technical modifications. We report the addition of unilateral host-to-allograft recurrent laryngeal nerve anastomosis to this model. Long-term survival experiments determine the feasibility of reinnervation studies of the allograft larynx with this new mode. A total of 59 transplants have been performed on histocompatible Munich Wistar rats, 36 with attempted unilateral allograft reinnervation. Because of the initially high operative mortality rates, additions and modifications of the original technique resulting in reproducibly enhanced survival are detailed. Factors critical to the functional study of this model with regard to reinnervation are elucidated. Preliminary data on allograft reinnervation are reported as confirmed by videodocumentation of vocal fold mobility, evoked and spontaneous electromyography, and glycogen-depletion studies.

Animals↗
PubMed1994

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.

Animals↗
PubMed1994

Effects of denervation on posterior cricoarytenoid muscle physiology and histochemistry.

The effects of chronic posterior cricoarytenoid muscle denervation were assessed at 3 and 7 months in 26 animals following resection of 10 cm of recurrent laryngeal nerve with stump ligation. The physiology of denervation was characterized by a decrease in contraction strength and an increase in contraction time. The reduction in contraction strength reflected the loss in muscle weight and atrophic changes in fiber density and diameter. A change in muscle composition occurred because of the increased susceptibility of fast-twitch (type 2) fibers to degeneration. However, the compositional change alone could not account for the slowing of muscle contraction. Muscle fibrosis was negligible at 3 months, but encompassed one third of the fiber population by 7 months. In view of the irreversible nature of fibrosis, this study suggested that clinical intervention to rescue denervated posterior cricoarytenoid muscle fibers should be delayed no longer than 7 months to improve the chances for full recovery.

Animals↗
PubMed1994

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.

Blindness↗
PubMed1994

Awake evoked electromyography recording from the chronically implanted rat.

Investigation of the effects of various factors on nerve regeneration has been compromised by the lack of an accurate and objective technique which can monitor dynamic changes in the status of nerve-muscle innervation over the entire course of regeneration. The approach of evoked electromyography (EEMG) was adopted to obtain temporal and quantitative data during nerve regeneration. Initially, transcutaneous nerve stimulation and percutaneous muscle recording was performed, but the approach was abandoned because of the high interest variability (20% average deviation) and requirement for anesthesia during testing. A new approach using chronically implanted stimulation and recording electrodes was adopted in an attempt to circumvent these problems. Initial acute studies performed in the hindlimb of the anesthetized rat identified stable EEMG recording sites with sciatic nerve stimulation. In a second study conducted in chronically implanted unanesthetized unrestrained animals, EEMG recording from these sites demonstrated remarkable stability with an average interest variability of only 5%. Preliminary results have been obtained with this technique in monitoring the progression of hindlimb reinnervation following crush and transection nerve injuries.

Animals↗
PubMed1992

An investigation of the potential for laser nerve welding.

Suture repair of a severed peripheral nerve is cumbersome, presents a focus for infection and neuroma formation, and does not always produce adequate stump alignment. An alternative form of repair is laser nerve welding, which is attractive because it does not introduce foreign material into the anastomotic site, it forms a circumferential seal, and it can be performed in difficult-to-reach areas. Laser repair has not been widely accepted both because the effect of laser irradiation on intact nerves is not well documented, and the anastomotic strength of the weld has been inferior to suture repair. In the first part of the present study, rat sciatic nerves were exposed and irradiated with increasing intensities from a Sharplan CO2 and KTP laser to document nerve damage as recorded by decreases in the peak compound action potential. A new technique of laser repair (S-Q weld) was then developed that involved harvesting subcutaneous tissue from the adjacent dermis, wrapping it around the two opposed nerve stumps, and lasering it to the epineurium to effect a weld. The strength of the S-Q weld (6.1 grams) was considerably greater than that produced by laser welding alone. The third phase of the study compared regeneration at 2 months in severed rat sciatic nerves repaired by either microsuture or S-Q weld. Analysis of the compound action potential values indicated that the number of regenerating fibers after laser repair was greater than that after suture repair, although a significant difference could not be demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1991

Recurrent laryngeal nerve avulsion for treatment of spastic dysphonia.

Treatment of spastic dysphonia by recurrent laryngeal nerve section has resulted in reproducibly good results in the early postoperative period in most patients. However, critical long-term follow-up has shown a high recurrence rate of adductor spasms by the third year after initial nerve section. A patient who developed recurring adductor spasms 1 year after nerve section was reexplored, with identification of neural regrowth into the distal segment of the recurrent laryngeal nerve. The technique of neural avulsion removing the distal nerve up to its insertion into the laryngeal muscles is described. Neural regrowth, which is just one of the possible mechanisms for recurrence of spastic dysphonia, should be prevented by this surgical modification. Twelve patients who have undergone neural avulsion primarily for spastic dysphonia are being followed up without recurrence of symptoms thus far. Although these results appear promising, this short follow-up that averages 1.5 years must be extended to firmly support these concepts.

Female↗
PubMed1990

Gadolinium-enhanced magnetic resonance imaging in Bell's palsy.

Inflammation of the facial nerve in Bell's palsy can be demonstrated on gadolinium-enhanced magnetic resonance imaging. We have studied a series of 17 Bell's palsy patients with gadolinium-enhanced magnetic resonance imaging, and the purpose of this paper is to report our findings and discuss their significance. Most acute Bell's palsy cases demonstrate facial nerve enhancement, usually in the distal internal auditory canal and labyrinthine/geniculate segments. Other segments demonstrate enhancement less often. Gadolinium enhancement occurs regardless of the severity of the paralysis and can persist after clinical improvement of the paralysis. The findings of this study corroborate other evidence that the segments of the facial nerve most often involved in Bell's palsy are the only segments that are most often enhanced with gadolinium-enhanced magnetic resonance imaging. The role of gadolinium-enhanced magnetic resonance imaging in the management of Bell's palsy patients is discussed.

Acute Disease↗
PubMed1988

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.

Action Potentials↗
PubMed1988

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%).

Biomechanical Phenomena↗
PubMed1988

A statistical study of ENoG test error.

Electroneurography (ENoG) is currently the most sophisticated and objective test available for assessing nerve degeneration in patients suffering from facial nerve paralysis. However, the test requires considerable experience before error due to intertest variability can be brought within reasonable limits. In a statistical study on normal participants, the error associated with two conventional recording techniques--optimized lead placement (OLP) and standardized lead placement (SLP)--was determined to be 17.8% and 20.7%, respectively. A significant increase in error was observed with the OLP approach (22.9%) if responses could not be monitored oscilloscopically, a common situation in patients with severe degeneration. In a final study, however, a previously unreported factor was found to significantly reduce test error: recording electrode size. In particular, unconventionally small recording electrodes (3 to 7 mm) produced as much as 4% less error when administering the technique.

Data Interpretation, Statistical↗
PubMed1985

Facial nerve recording from the eardrum: a possible method for evaluating idiopathic facial nerve paralysis.

A noninvasive technique has been developed for recording from the the facial nerve within the fallopian canal. Following transcutaneous stimulation of the nerve on the face, an antidromic nerve potential can be detected with electrodes placed on the eardrum and enhanced by the technique of averaging. In studies conducted on cats and normal human subjects it has been determined that the primary recording site of the nerve potential is along the tympanic segment of the nerve just distal to the geniculate ganglion. Disturbances in nerve conduction caused by an experimental lesion produced changes in the recorded nerve potential. Thus it seems likely that this technique could assess a developing lesion in a patient with idiopathic facial nerve paralysis. A more accurate and earlier prognosis could be obtained than with conventional peripheral nerve testing techniques, since the severity of the developing lesion itself could be assessed.

Animals↗
PubMed1982

Stimulating and recording from axons within their myelin sheaths: a stable and nondamaging method for studying single motor units.

The contractile properties and activity patterns of single thyroarytenoid motor units were determined by stimulating and recording from their motoneuron axons within the recurrent laryngeal nerve. Most micropipette penetrations were within the myelin sheaths of axons but were functionally similar to actual axon impalements with respect to activation and recording of action potentials. Sheath penetrations were, however, less damaging to axons and were preferred for that reason. A myelin sheath approach combined the advantages of commonly used extra-axonal and intracellular methods for studying motor unit properties without their disadvantages. Specifically, the technique was stable, noninjurious in nature, and ensured stimulation and recording from the same motoneuron.

Animals↗
PubMedDate not supplied

Control of paralysed axial muscles by electrical stimulation.

The function of a paralysed axial (laryngeal, facial, extraocular) muscle could conceivably be restored if it were made to contract again like its contralateral partner. A muscle stimulation device was designed and constructed so that the stimulus delivered to a given paralysed muscle was modulated by a signal reflecting the contractile state of its contralateral partner. Studies in dog larygneal muscles indicate that paralysed muscles stimulated by such an open-loop device could mimic their partners. However, their tracking accuracies were limited by the nature of their stimulus-reponse characteristics. On the other hand, significantly greater tracking accuracies were observed if a closed-loop device was employed, that is, if feedback information from the stimulated muscles was also used to control the device stimulus level. Considerations in implanting such a (closed-loop or open-loop) device in paralysed axial muscles for chronic stimulation are discussed.

Animals↗