Munehiro Hamaguchi

Observation of Velopharyngeal Closure Patterns Following Isolated Stimulation of Levator Veli Palatini and Pharyngeal Constrictor Muscles

This study, using mongrel dogs, showed the individual movements caused by the levator veli palatini muscle (LVP) and pharyngeal constrictor (PC) contraction, induced by electrical stimulation to each peripheral motor nerve. Each bilateral peripheral motor nerve of the LVP and PC muscles was isolated and stimulated electrically to induce the individual contraction of bilateral LVP and PC muscles. The movements were visualized by use of a fiberscope. Vertical movement of the middle soft palate was observed mainly at LVP contraction. Circular closure in the posterior region of the velopharynx was induced by contraction of the PC muscle. The posterior and lateral wall movements clearly occurred following PC contraction.

Measurement of Velopharyngeal Movements Induced by Isolated Stimulation of Levator Veli Palatini and Pharyngeal Constrictor Muscles

The levator veli palatini (LVP) and superior pharyngeal constrictor muscles (PC) close the velopharynx. However, for the velopharyngeal movements to be understood in detail, each muscle contraction must be analyzed precisely. This study was performed to clarify the velopharyngeal movement which was induced by a single muscle contraction, LVP or PC. Using a nasopharyngeal fiberscope, we analyzed the velopharyngeal movement associated with the contraction of the LVP and PC muscles in mongrel dogs. To elicit the maximal contraction of each muscle, we applied repetitive electrical stimulation to each peripheral nerve efferent to the LVP or PC muscle. Stimulation with a frequency of 77 Hz and 83 Hz induced maximal tension in the LVP and PC muscles, respectively, in isometric contraction. In a second series of experiments, fiberscopic views of the velopharyngeal movements associated with each muscles maximal contraction were recorded. The degree of closure was calculated at several sections. The LVP muscle pulled the caudal fourth of the soft palate, while the PC projected the posterior wall at the level of the caudal end of the soft palate. The PC muscle also projected the lateral wall of the velopharynx. The effect of LVP contraction on the lateral wall was very small. These results show that the velopharyngeal movement associated with LVP contraction is very different from that with PC contraction.

Activities of superior pharyngeal constrictor and levator veli palatini muscles related to respiration in dogs.

OBJECTIVE This study, using mongrel dogs, attempted to delineate the respiratory activity of two closure muscles of the velopharynx, the levator veli palatini (LVP) and superior pharyngeal constrictor (PC) muscles. METHOD Fifteen mongrel dogs were given tracheotomies, with intratracheal tubes being connected to their respiratory circuits. Activities of the PC and LVP muscles were recorded electromyographically, and the effects of PaO2 and PaCO2 were analyzed along with the effects of lung inflation intratracheally with O2 and N2. RESULTS Under hypoxic conditions, expiratory LVP activity was observed while PC activity diminished. The effects of lung inflation on both LVP and PC activities were also studied. The activities of both muscles were enhanced by lung inflation. CONCLUSION It was thus suggested that the roles of both muscles during velopharyngeal closing movements are not the same.

Velopharyngeal Closure Pattern Exerted by Contraction of the Pharyngeal Constrictor Muscle in Dogs

OBJECTIVE This study was performed to investigate aspects of velopharyngeal closure demonstrated by movements of the parapharyngeal wall under various physiological conditions and especially the stimulation of several intrapneumonal receptors. MATERIALS AND METHODS Fifteen mongrel dogs were anesthetized and a nasopharyngeal fiberscope was inserted from the oronasal fistula at the center of the hard palate, with the tip fixed around the choana. Mechanical and chemical stimulation was applied, and ongoing velopharyngeal movements were observed. In each case examined, the muscle nerve located under the bilateral levator veli palatini (LVP) was severed. RESULTS Two different closure patterns were recognized between rebreathing and deglutition. Chemical stimulation of the pulmonary irritant receptor and type-J receptor induced a sphincteric tight closure of the velopharynx but only a weak inward movement of the lateral pharyngeal wall at lung inflation. CONCLUSION The movements of the parapharyngeal wall, mainly represented by the pharyngeal constrictor muscles contraction, are facilitated as a sphincteric velopharyngeal closure under reflexive movements such as deglutition or gagging.

Saliva secretion stimulated by grafted nerve in submandibular gland allograft in dogs.

Background. Recent studies have described submandibular gland allografts in animal models; however, the amount of saliva secretion or nervous regeneration in those animals have not been reported. Herein, we investigated saliva secretion from submandibular gland allografts in beagle dogs. Methods. Using a vascularized submandibular gland transplantation method, we extracted portions of the submandibular gland including the duct from beagle dogs and placed them into the submental region of age- and weight-matched dogs. Differences in the amount of saliva secretion and histologic appearance were compared based on the existence of chorda tympani branches in the allograft. Results. At 10 weeks after transplantation, the amount of resting saliva in the group grafted with the nerve was clearly increased, whereas the quantity of that in the group that underwent transplantation without the nerve was quite low. In the former group, responses were demonstrated after taste stimulation and electronic nerve stimulation. Conclusions. Our results showed a clear relationship between the presence of a nerve in grafted submandibular glands and saliva secretion.

Effects of subglottal air pressure on velopharyngeal muscle activity in dogs.

OBJECTIVE To analyze the effects of airflow in the larynx on activity of the levator veli palatini and pterygopharyngeal muscles. DESIGN Ten adult beagle dogs were anesthetized with sodium pentobarbital. In each dog, two tracheal tubes were inserted subsequent to tracheotomy, one in the direction of the vocal folds and the other toward the lungs for respiration. In the first of three experiments, the effect of artificial airflow on electromyographic activity of the levator and pterygopharyngeal muscles was studied. In the second experiment, the effect of air pressure beneath the vocal folds on the activity of these muscles was studied. For the third experiment, the larynx was isolated surgically without cutting the bilateral superior laryngeal nerves and the effect of airflow through it examined. RESULTS AND CONCLUSION Both outward airflow and higher pressure enhanced expiratory activity of the levator and pterygopharyngeal muscles. Receptors in the subglottal area play major roles in this enhancement. Furthermore, an increase in air pressure during expiration enhances closure of the velopharynx.

Inferior Alveolar Nerve Regeneration After Bifocal Distraction Osteogenesis in Dogs

PURPOSE Bifocal distraction osteogenesis has been shown to be a reliable method for reconstructing missing bone segments. However, no reports have been published regarding inferior alveolar nerve regeneration during this procedure. We assumed that the nerve could regenerate with the bone regeneration during bifocal distraction, if the nerve had been saved at a mesial site of the transport disc. In the present study, we investigated that possibility in dogs. MATERIALS AND METHODS Using a bifocal distraction osteogenesis method, we produced a 10-mm mandibular defect, including the nerve defect, and distracted the transport disc at a rate of 1 mm/day in 12 dogs. The nerve was saved at the mesial site of the transport disc. The regenerated nerve was evaluated by a jaw opening reflex examination performed once daily. Histologic examinations with hematoxylin-eosin and immunohistochemical staining with neurofilament and S-100 antibody were also performed on all dogs after death at 3, 6, and 12 months after the first operation. RESULTS The jaw opening reflex had recovered in all dogs. The average period of recovery was 109.5 ± 24.7 days. On histologic examination, although consecutive nerves were observed in all areas, cellular nerve fascicles were seen, consistent with wallerian degeneration at 3 and 6 months in the nerve connection area on the distal side of the transport disc. CONCLUSIONS Our results have indicated that inferior alveolar nerve regeneration after bifocal distraction osteogenesis is successful in dogs. Although our research is still at the stage of animal experiments, future application in humans can be considered to be possible.

Electrophysiologic evaluation of inferior alveolar nerve regenerated by bifocal distraction osteogenesis in dogs.

Background: Bifocal distraction osteogenesis has been shown to be a reliable method for reconstructing missing bone segments. However, there are no reports regarding inferior alveolar nerve regeneration during bifocal distraction. In the present study, the authors evaluated the function of inferior alveolar nerve regenerated by bifocal distraction after segmental resection in the mandibles of dogs. Methods: Using a bifocal distraction osteogenesis method, the authors produced a 10-mm mandibular defect and distracted the transport disk at a rate of 1 mm/day. The regenerated inferior alveolar nerve was evaluated by electrophysiologic analysis that was performed on all dogs after euthanasia at 3, 6, and 12 months after the first operation. Results: At 6 and 12 months, stable evoked potential measurements were obtained from the nerves throughout the study on electrophysiologic analyses. Conclusions: The authors’ results indicate that the inferior alveolar nerve regenerated by bifocal distraction osteogenesis functioned electrophysiologically at 6 months after the first operation. Although our research is still at the stage of animal experiments, future application in humans is considered to be possible.

Contraction properties of the superior pharyngeal constrictor muscle

OBJECTIVE The mechanical contraction property of the superior pharyngeal constrictor (PC) muscle was analyzed and compared with the levator veli palatini (LVP) muscle. DESIGN Twenty adult dogs anesthetized with sodium pentobarbital were used. RESULTS The isometric contraction curves of LVP and PC were recorded after direct electric stimulation to each muscle. The contraction time of isometric twitch contraction of the superior PC muscles was 30.3+/-5.25 msec, and the half relaxation time was 22.97+/-5.44 msec. The summation curve was observed at a stimulus frequency above 20 Hz of a repetitive pulse stimulus frequency of 85 Hz. CONCLUSIONS The mechanical contraction properties of the PC muscle are similar to those of the LVP, but with more aspects that are characteristic of a fast twitch muscle.