PURPOSE: The most important function of the larynx is airway protection which is provided through a polysynaptic reflex closure triggered by the receptors in the glottic and supraglottic mucosa, evoking the reflex contraction of the laryngeal muscles especially by strong adduction of vocal cords. Based on the hypotheses that central facilitation is essential for this bilateral adductor reflex and that its disturbance can result in weakened laryngeal closure, we designed this study to elucidate the effect of central facilitation on this protective reflex. MATERIALS AND METHODS: Seven adult, 20 kg mongrel dogs underwent evoked response laryngeal electromyography under 0.5 to 1.0 MAC (minimum alveolar concentration) isoflurane anesthesia. The internal branch of the superior laryngeal nerve was stimulated through bipolar platinum-iridium electrodes, and recording electrodes were positioned in the ipsilateral and contralateral thyroarytenoid muscles. RESULTS: Ipsilateral reflex closure was consistantly recorded regardless of anesthetic levels. However, contralateral reflex responses disappeared as anesthetic levels were deepened. Additionally, late responses (R2) were detected in one animal at lower level of anesthesia. CONCLUSIONS: Deepened level of anesthesia affects central facilitation and results in the loss of the crossed adductor reflex, predisposing to a weakened glottic closure response. Precise understanding of this effect may possibly provide a way to prevent aspiration in unconscious patients.
Anesthesia/methods ; Animals ; Dogs ; Glottis/*physiology ; Laryngeal Nerves/physiology ; *Reflex

OBJECTIVETo study the behaviors of normal recurrent laryngeal nerve and superior laryngeal nerve evoked electromyography, to know the reference values of related parameters.

METHODSThirty six normal subjects were studied with laryngeal evoked electromyography. The latent period, duration, and amplitude of the evoked potentials (EP) recorded in laryngeal muscles were investigated.

RESULTSThe latent period of the EP recording from the thyroarytenoid muscles (TA), after stimulating recurrent laryngeal nerve (RLN), was (1.13 - 2.25) ms (x +/- 2s), that of TA after stimulating vagus nerve (VN) was (2.57 - 5.85) ms. There were significant differences in the latent periods of EP between RLN and VN (P < 0.01), and the latent periods of EP recording from TA after stimulating right cervical part of VN, (2.01 - 4. 53) ms (x +/- 2s) were significant shorter than those of left, (3.70 - 6.98) ms (x +/- 2s, P < 0.01). The durations of the EP were somewhat different but not significant. The amplitudes of the EP in different laryngeal muscles changes markedly. The wave form and latent period of the EP recording from cricothyroid muscle (CT), after stimulating the external branch of superior laryngeal nerve (SLN), was similar with the EP of RLN, the reflective EP R1 and R2 could be recorded from TA, posterior cricoarytenoid muscles (PCA), CT after stimulating the internal branch of SLN.

CONCLUSIONSThe characteristics of the EP recorded in laryngeal muscles after stimulation of RLN, SLN and VN are different. The latent period, duration and amplitude are important parameters in the evaluation of laryngeal nerves function, the latent period is the most important parameter.

Adult ; Aged ; Electromyography ; Evoked Potentials ; Female ; Humans ; Laryngeal Muscles ; innervation ; physiology ; Laryngeal Nerves ; physiology ; Male ; Middle Aged ; Recurrent Laryngeal Nerve ; physiology ; Reference Values

PURPOSE: The purpose of this study was to investigate the activation of the respiratory centers during insufflation of the larynx with CO2 at different flow rates and concentrations. MATERIALS AND METHODS: The experiments were carried out in spontaneous air breathing rabbits, anesthetized with thiopental sodium (25mg kg(-1) i.v.). The larynx was separated from the oropharyngeal cavity and the trachea. The tidal volume (VT) and respiratory frequency (f min(-1)) were recorded from the lower tracheal cannula. The respiratory minute volume (VE) was calculated, the action potentials from the right phrenic nerve were recorded and the inspiratory (TI) and expiratory (TE) periods and the mean inspiratory flow rate (VT/TI) were calculated. The larynx was insufflated at flow rates of 500mL min(-1) and 750mL min(-1), with 7 and 12% CO2-Air by means of a respiratory pump. RESULTS: Insufflation of the larynx, with both gas mixtures, decreased the f and VT significantly. The TI and TE were found to increase significantly due to the decreasing in f. There was a significant decrease in VT/TI ratio. Following bilateral midcervical vagotomy, on the passing of both gas mixtures, significant decreases were observed in the VT, and the responses of f, TI and TE were abolished. After cutting the superior laryngeal nerve, the responses of the VT to both gas mixtures were abolished. CONCLUSION: In conclusion, the results of this study purpose that the stimulation of the laryngeal mechanoreceptors by the effect of hyper- capnia decreases the activation of the respiratory center
Air ; Animals ; Carbon Dioxide/chemistry/*pharmacology ; Female ; Laryngeal Nerves/drug effects/physiology ; Male ; Mechanoreceptors/drug effects/physiology ; Rabbits ; Reflex/*drug effects/physiology ; *Respiratory Mechanics/drug effects ; Tidal Volume