James T. Heaton

Early versus late injection medialization for unilateral vocal cord paralysis

To evaluate whether the timing of early (≤6 months from time of nerve injury) vs. late (>6 months) injection medialization laryngoplasty impacts the need for subsequent open‐neck reconstruction to restore vocal function in patients with unilateral vocal cord paralysis.

Vocal control pathways through the anterior forebrain of a parrot (Melopsittacus undulatus)

A feature of the telencephalic vocal control system in the budgerigar (Melopsittacus undulatus) that has been hypothesized to represent a profound difference in organization from the oscine vocal system is its reported lack of an inherent circuit through the anterior forebrain. The present study reports anatomical connections that indicate the existence of an anterior forebrain circuit comparable in important ways to the “recursive” pathway of oscine songbirds. Results from anterograde and retrograde tracing experiments with biocytin and fluorescently labeled dextran amines indicate that the central nucleus of the anterior archistriatum (AAc) is the source of ascending projections upon the oval nuclei of the anterior neostriatum and ventral hyperstriatum (NAo and HVo, respectively). Efferent projections from the latter nuclei terminate in the lateral neostriatum afferent to AAc, thereby forming a short recurrent pathway through the pallium. Previously reported projections from HVo and NAo upon the magnocellular nucleus of the lobus parolfactorius (LPOm), and from LPOm onto the magnocellular nucleus of the dorsal thalamus (DMm; G.F. Striedter [1994] J. Comp. Neurol. 343:35–56), are confirmed. A specific projection from DMm onto NAom is also demonstrated; therefore, a recurrent pathway through the basal forebrain also exists in the budgerigar vocal system that is similar to the anterior forebrain circuit of oscine songbirds. Parallels between these circuits and mammalian basal ganglia‐thalamo‐cortical circuits are discussed. It is hypothesized that vocal control nuclei of the avian anterior neostriatum may perform a function similar to the primate supplemental motor area. J. Comp. Neurol. 377:179–206, 1997.

Ambulatory monitoring of disordered voices

Objectives: Recently developed systems for ambulatory monitoring of voice use employ miniature accelerometers placed at the base of the anterior neck to sense phonation. As it is hoped that such systems will help improve the clinical assessment and management of voice disorders, this study was undertaken to determine the impact of dysphonia severity on the accuracy of accelerometer-based estimates of vocal function. Methods: Simultaneous recordings were made of oral acoustic (microphone) and neck skin acceleration signals for 6 normal speakers and 18 patients with voice disorders (mild to severe dysphonia) as they performed several speech tasks. Measures of phonation time, fundamental frequency, and sound pressure level were extracted from the Two types of signals and compared. Results: It was generally demonstrated that accelerometer-based measures closely approximated corresponding measurements obtained from a microphone signal across all levels of dysphonia severity. Furthermore, there was evidence that in some cases the accelerometer may actually represent a more robust approach for estimating phonation parameters in disordered voices. Conclusions: The results generally support the recent application of accelerometers as phonation sensors in ambulatory voice monitoring systems that can be used in the clinical assessment and management of voice disorders.

Analysis of the Forces and Position Required for Direct Laryngoscopic Exposure of the Anterior Vocal Folds

The sniffing position is traditionally considered optimal for direct laryngoscopic examination of the vocal folds. This study examined head and neck positions associated with ideal exposure of the anterior glottal commissure with a variety of laryngoscopes. A prospective investigation was done in 20 patients by comparing the force required to expose the anterior vocal folds by utilizing 3 head and neck positions with 3 different-sized tubular laryngoscopes. The completeness of anterior glottal exposure was rated and the force required to achieve this exposure was measured with a strain gauge. Three positions relating the atlanto-occipital and cervicothoracic vertebrae were analyzed: 1) extension-extension, 2) sniffing: extension-flexion, and 3) flexion-flexion. Head and neck position and laryngoscope size were both statistically significant factors for achieving complete anterior vocal fold exposure. Regardless of the laryngoscope, the number of patients in whom complete exposure could be achieved increased gradually when the position was changed from extension-extension to extension-flexion to flexion-flexion. Complete exposure was inversely related to larger laryngoscope size. According to the data herein, the flexion-flexion position provides the best glottal exposure for endotracheal intubation in those patients who are anatomically predisposed to difficulty in direct examination of the glottis. Because this places the laryngoscope lumen in a vertical position, this position is inappropriate for microlaryngoscopy. The study reinforced the concept that the sniffing position is the optimal position for microlaryngoscopy because it enables the use of the largest-lumened laryngoscope. This facilitates ideal exposure of the anterior vocal folds, which is necessary for phonomicrosurgery.

A system for studying facial nerve function in rats through simultaneous bilateral monitoring of eyelid and whisker movements

The occurrence of inappropriate co-contraction (synkinesis) of facially innervated muscles in humans is a common sequela of facial nerve injury and recovery. We have developed a system for studying facial nerve function and synkinesis in restrained rats using non-contact opto-electronic techniques that enable simultaneous bilateral monitoring of eyelid and whisker movements. Whisking is monitored in high spatio-temporal resolution using laser micrometers, and eyelid movements are detected using infrared diode and phototransistor pairs that respond to the increased reflection when the eyelids cover the cornea. To validate the system, 8 rats were tested with multiple 5-min sessions that included corneal air puffs to elicit blink and scented air flows to elicit robust whisking. Four rats then received unilateral facial nerve section and were tested at weeks 3-6. Whisking and eye blink behavior occurred both spontaneously and under stimulus control, with no detectable difference from published whisking data. Proximal facial nerve section caused an immediate ipsilateral loss of whisking and eye blink response, but some ocular closures emerged due to retractor bulbi muscle function. The independence observed between whisker and eyelid control indicates that this system may provide a powerful tool for identifying abnormal co-activation of facial zones resulting from aberrant axonal regeneration.

Effects of 532 nm pulsed-KTP laser parameters on vessel ablation in the avian chorioallantoic membrane: Implications for vocal fold mucosa

Objectives: Selective vascular ablation (photoangiolysis) using pulsed lasers that target hemoglobin is an effective treatment strategy for many vocal fold lesions. However, vessel rupture with extravasation of blood reduces selectivity for vessels, which is frequently observed with the 0.45‐ms, 585‐nm pulsed dye laser. Previous studies have shown that vessel rupture is the result of vaporization of blood, an event that varies with laser pulse width and pulse fluence (energy per unit area). Clinical observations using a 532‐nm wavelength pulsed potassium‐titanyl‐phosphate (KTP) laser revealed less laser‐induced hemorrhage than the pulsed dye laser. This study investigated settings for the pulsed KTP laser to achieve selective vessel destruction without rupture using the avian chorioallantoic membrane under conditions similar to flexible laryngoscopic delivery of the laser in clinical practice.

Rodent Facial Nerve Recovery After Selected Lesions and Repair Techniques

Background: Measuring rodent facial movements is a reliable method for studying recovery from facial nerve manipulation and for examining the behavioral correlates of aberrant regeneration. The authors quantitatively compared recovery of vibrissal and ocular function following three types of clinically relevant nerve injury. Methods: One hundred seventy-eight adult rats underwent facial nerve manipulation and testing. In the experimental groups, the left facial nerve was either crushed, transected, and repaired epineurially, or transected and the stumps suture-secured into a tube with a 2-mm gap between them. Facial recovery was measured for the ensuing 1 to 4 months. Data were analyzed for whisking recovery. Previously developed markers of co-contraction of the upper and midfacial zones (possible synkinesis markers) were also examined. Results: Animals in the crush groups recovered nearly normal whisking parameters within 25 days. The distal branch crush group showed improved recovery over the main trunk crush group for several days during early recovery. By week 9, the transection/repair groups showed evidence of recovery that trended further upward throughout the study period. The entubulation groups followed a similar recovery pattern, although they did not maintain significant recovery levels by the study conclusion. Markers of potential synkinesis increased in selected groups following facial nerve injury. Conclusions: Rodent vibrissal function recovers in a predictable fashion following manipulation. Generalized co-contraction of the upper and midfacial zones emerges following facial nerve manipulation, possibly related to aberrant regeneration, polyterminal axons, or hypersensitivity of the rodent to sensory stimuli following nerve manipulation.

A novel method of head fixation for the study of rodent facial function.

The rodent vibrissial system offers an excellent model for the study of both sensory and motor function. It has been widely employed to gather data pertaining to sensory and motor function involving the 5th and 7th cranial nerves and the central nervous system. Existing methods of head fixation for precise measurements of ocular and vibrissial function involve exposing the cranium and applying dental cement from which two or more threaded rods emerge. This common approach is suboptimal, requiring a relatively complicated implantation procedure, and results in a large, chronic interface between the scalp and environmentally exposed implant material attached to the skull. Here we describe a head fixation device that is inexpensive, easy to build, less prone to infection, preserves access to the cranial midline, and permits repeated measurements over many months.

Carbon dioxide laser fiber for laryngeal cancer surgery.

Objectives: The carbon dioxide laser has evolved to be the premier dissecting instrument for hemostatic cutting during endolaryngeal cancer resection. However, dissection is limited to mirror-reflected line-of-sight delivery of the laser. A recently developed flexible, hollow photonic bandgap fiber (PBF) appears to offer advantages in endolaryngeal dissection. Methods: The suitability of the PBF for human application was evaluated in a canine experiment in which human surgical procedures for microlaryngoscopic en bloc partial laryngectomy were simulated. The specimens that were resected endoscopically and the completion laryngectomy specimen were evaluated histologically. Results: Observations from this experiment revealed that en bloc partial laryngectomy procedures were substantially easier to achieve as compared with prior experience in humans. This improvement resulted from three factors: 1) enhanced tangential dissection due to increased angulation of the laser energy, 2) enhanced procedural orientation due to proprioception of the tissues in contact mode, and 3) improved hemostasis. Histopathologic analysis of the resection margins revealed minimal thermal trauma. Conclusions: The PBF shows substantial promise for human application in endoscopic partial laryngectomy. It will likely enhance the ability of any surgeon to extend his or her indications for performing endoscopic laryngeal cancer resections regardless of philosophy (en bloc resection or piecemeal).

Functional anatomy of forebrain vocal control pathways in the budgerigar (Melopsittacus undulatus)

Budgerigars throughout life are capable of learning to produce many different sounds including those of human speech. Like humans, budgerigars use multiple craniomotor systems and coordinate both orosensory and auditory feedback in specialized forebrain nuclei. Although budgerigar auditory-vocal learning has a different evolutionary origin from that of human speech, both the human and budgerigar systems can control F0 and can alter the distribution of energy in spectral bands by adjusting the filter properties of the vocal tract. This allows budgerigars to produce an extremely diverse array of calls including many broadband and highly complex sounds.