Faculty Bibliography

Malformations of the arterial and venous systems often are manifested in the head and neck. Low-flow venous malformations are generally benign lesions; however, complications, such as bleeding, obstruction, pain, or cosmetic deformities, may warrant surgical intervention. Treatment of these lesions can be challenging. Laser photocoagulation, particularly with the neodymium-yttrium aluminum garnet (Nd-YAG) laser, has been successful in the majority of patients, with minimal morbidity and good results. Thirty-two patients with low-flow venous malformations of the head and neck were treated with the Nd-YAG laser using low-power density and intermittent short exposures in a punctate nonoverlapping technique. When possible, two glass slides were used to compress the lesion. There was excellent regression with minimal damage to the surrounding tissue. No major complications or morbidity, postoperative pain, or mortality occurred. Lesions occurring in some areas of the head and neck would not have been amenable to standard surgical excision. Follow-up period has ranged from 1 to 8 years. Nd-YAG laser photocoagulation has proved safe and effective for treatment of low-flow vascular malformations of the head and neck

Subglottic stenosis remains a difficult clinical problem with varied management approaches. An accepted procedure has been anterior and posterior cricoid incisions through an external approach for treatment of severe stenoses without a tracheotomy. The holmium:yttrium-aluminum-garnet laser, 2.1 microns wavelength with a pulsed output, is transmissible through standard fibers and ablates soft tissue and cartilage with minimal surrounding damage. This study in in vitro and in vivo animal models shows that this new laser can be used to incise the anterior and posterior cricoid and tracheal cartilages with precise control and may be suitable for endoscopic laryngotracheoplasty

Two experiments investigating the effects of auditory stimulation delivered via a Nucleus multichannel cochlear implant upon vowel production in adventitiously deafened adult speakers are reported. The first experiment contrasts vowel formant frequencies produced without auditory stimulation (implant processor OFF) to those produced with auditory stimulation (processor ON). Significant shifts in second formant frequencies were observed for intermediate vowels produced without auditory stimulation; however, no significant shifts were observed for the point vowels. Higher first formant frequencies occurred in five of eight vowels when the processor was turned ON versus OFF. A second experiment contrasted productions of the word 'head' produced with a FULL map, OFF condition, and a SINGLE channel condition that restricted the amount of auditory information received by the subjects. This experiment revealed significant shifts in second formant frequencies between FULL map utterances and the other conditions. No significant differences in second formant frequencies were observed between SINGLE channel and OFF conditions. These data suggest auditory feedback information may be used to adjust the articulation of some speech sounds

A two-microphone dereverberation technique was evaluated by obtaining speech recognition measures and preference judgments from normal-hearing and hearing-impaired listeners. Monaural speech recognition performance was measured for two reverberation conditions (0.4 second and 1.2 seconds) with and without processing. Binaural speech recognition performance was also measured for the unprocessed conditions. In addition, paired-comparison judgments of preference were obtained for all combinations of the processed and unprocessed monaural stimuli. For both groups of subjects, scores at the shorter reverberation time were significantly higher than scores for the longer reverberation time. For the normal-hearing subjects, processing to dereverberate had no significant effect on speech recognition performance. Binaural presentation of the unprocessed signal yielded significantly higher scores. For the hearing-impaired subjects, performance was significantly better in the unprocessed condition than the processed condition, but was not significantly different from the binaural condition. Paired-comparison judgments revealed differences in patterns of preference between normal-hearing and hearing-impaired listeners

In orthogonal polynomial compression, the short-term speech spectrum is first approximated by a family of orthogonal polynomials. The coefficients of each polynomial, which vary over time, are then adjusted in terms of their average value and range of variation. These adjustments can be used to compress (or expand) temporal variations in the average level, slope, and various forms of curvature of the short-term speech spectrum. The analysis and reconstruction of the short-term speech spectrum using orthogonal polynomials was implemented using a digital master hearing aid. This method of compression was evaluated on eight sensorineurally hearing-impaired listeners. Speech recognition scores were obtained for a range of compression conditions and input levels with and without frequency shaping. The results showed significant advantages over conventional linear amplification when temporal variations in the average level of the short-term spectrum were compressed, a result comparable to that obtained with conventional amplitude compression. A subset of the subjects showed further improvement when temporal variations in spectrum slope were compressed, but these subjects also showed similar improvements when frequency shaping was combined with level-only compression. None of the subjects showed improved speech recognition scores when variations in quadratic curvature were compressed in addition to level and slope compression

Three postlingually deafened adults who received cochlear implants read passages before and after their prostheses were activated while their lung volumes were measured with an inductive plethysmograph that transduced the cross-sectional areas of the speaker's chest and abdomen. Lung volumes at the initiation and termination of the speakers' expiratory limbs, their average air flow, and the volume of air they expended per syllable were derived from tracings of calibrated lung volume displayed by computer. The activation of the speakers' cochlear prostheses was followed in every case by a significant change in average airflow, which rose for two subjects with initially low flow rates and fell for one subject who had a much higher average preimplant flow rate. These changes in average flow rate were accompanied by corresponding changes in volume of air expended per syllable, statistically reliable in two of the three cases. There were no significant changes in the levels at which speakers initiated their expiratory limbs, but one speaker, after his prosthesis was activated, reliably increased the level of air in his lungs at the end of expiratory limbs to an average value that no longer required him to draw on expiratory reserve volume

This study examined the morphological development of single inhibitory arborizations in the gerbil central auditory brain stem. Using a brain slice preparation, neurons of the medial nucleus of the trapezoid body (MNTB) were filled with horseradish peroxidase (HRP), and their complete arborizations were analyzed along the tonotopic axis of the lateral superior olive (LSO). The projections in neonatal animals displayed well-defined arbors that were ordered appropriately within the LSO. It was evident from the axonal pathways that the MNTB afferents could correct for projection errors after reaching the postsynaptic population. As development progressed, a number of arbors established diffuse or inappropriate projections within the LSO. These immature arborizations were no longer apparent by 18-25 days postnatal. The anatomical specificity of arbors at 12-13 and 18-25 days was quantified by measuring the distance that terminal boutons spread across the frequency axis. There was a significant reduction of this distance in older animals. In addition, there was a significant reduction in the mean number of boutons per arbor between 12-13 days and 18-25 days. The maximum nucleus cross-sectional area continued to increase through 15-16 days, indicating that the refined arbors occupied an even smaller fraction of the postsynaptic structure. Taken together, these observations suggest that central inhibitory arbors form exuberant contacts that must be eliminated during development