Laryngeal Activity Research Articles

Responses of laryngeal receptors to intralaryngeal CO2 in the cat.

1. We recorded afferent activities of single fibres in the superior laryngeal nerves of decerebrate or anaesthetized, paralysed cats while 3, 5 and 10% CO2 was added to a constant flow of warm, humidified air through the isolated upper airway. 2. Fifty-three receptors with discharge frequencies modulated by intralaryngeal CO2 were studied. Of these, forty-eight showed CO2-induced attenuation of their firing rates. Pulses of 3, 5 or 10% CO2, alternating with air at intervals ranging from 1.5 to 60 s, also diminished the discharge frequencies. This diminution was greater with higher CO2 concentrations and longer pulse durations. 3. Five of the fifty-three receptors were stimulated by intralaryngeal CO2. The discharge frequencies of these units increased slowly and by only a few impulses per second during CO2 exposure. 4. Thirty-four of the CO2-sensitive receptors were tested with other stimuli, including water, saline, positive and negative intralaryngeal pressures and cold air. The responses to these stimuli varied among receptors, but many of the units that reduced their frequencies with intralaryngeal CO2 were consistently stimulated by positive and/or negative intralaryngeal pressures. 5. Thirty-six of the receptors were anatomically located by probing the upper airway. Twenty-six were in the larynx, and ten were in the rostral trachea, within 5 mm of the cricoid cartilage. 6. The results, which are directly applicable to the investigation of reflex responses reported in the preceding paper, indicate that the predominant initial response to intralaryngeal CO2 under the conditions of these studies is attenuation of laryngeal receptor activity.

Synaptic interaction between medullary respiratory neurones during apneusis induced by NMDA-receptor blockade in cat.

1. Termination of inspiration is an essential component of respiratory rhythm generation and its perturbation can result in apneusis, i.e. significant prolongation of mechanisms, we studied the postsynaptic events in respiratory neurones during apneustic respiratory periods, and compared them to normal respiratory cycles. 2. Experiments were performed in pentobarbitone-anaesthetized, paralysed, thoracotomized cats ventilated with a constant volume or a cycle-triggered constant pressure pump. Apneusis, separated by normal cycles, was induced as follows: the animal was ventilated by a cycle-triggered pump that normally inflated the lungs during the inspiratory burst of phrenic nerve discharge. The NMDA-receptor blocker MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5, 10-iminemaleate] (0.3-0.7 mg/kg) was administered intravenously, and, for designated breaths, inflation of the lungs was withheld during neural inspiration. 3. Membrane potential trajectories of forty-one late expiratory (E-2) and eight postinspiratory (PI) neurones of the caudal ventral respiratory group were analysed before and/or after MK-801 administration, during normal and apneustic periods. 4. Before MK-801 administration, withholding lung inflation caused modest (10-20%) lengthening of the inspiratory period; after MK-801 administration, withholding inflation caused apneusis. Provided that the lungs were inflated during the inspiratory phase, the temporal pattern of phrenic nerve, recurrent laryngeal nerve and membrane potential trajectories of E-2 and PI neurones were not significantly altered by MK-801. Apneusis following NMDA-receptor blockade produced consistent changes in the synaptic activation patterns of E-2 neurones. In particular, the slow late inspiratory-related depolarization pattern of E-2 neurones was consistently retarded during apneustic inspiratory phases when compared to normal inspiratory phases. This was due to continuation of Cl(-)-mediated synaptic inhibition of E-2 neurones. Superior laryngeal nerve stimulation stopped apneusis and sustained membrane hyperpolarization of E-2 neurones similar to lung inflation. 5. During the plateau phase of apneusis, correlated 10-20 Hz oscillations could be observed in the integrated phrenic and recurrent laryngeal nerve activities as well as in the membrane potential of E-2 neurones. 6. We conclude that: (i) the prolonged inhibition of E-2 neurones during apneusis is indicative of the process responsible for the prolongation of the inspiratory phase.(ABSTRACT TRUNCATED AT 400 WORDS)

The respiratory activity of the superior laryngeal nerve in the rat

The aim of this study was to characterize the laryngeal afferent activity of the rat. The animals were anesthetized and breathing spontaneously. Laryngeal afferent activity was recorded from both the whole superior laryngeal nerve (SLN) and from single fibers isolated from this nerve. An overall inspiratory augmenting activity was observed in the whole SLN during tracheostomy breathing, tracheal occlusion and upper airway breathing, but an expiratory augmenting activity was present during upper airway occlusion. The inspiratory modulated activity was abolished by bilateral section of the hypoglossal nerves but not the recurrent laryngeal nerves. A great number of receptors (46/80, 58%) were identified as ‘drive’ receptors, and others as ‘pressure’ (22/80, 28%) and ‘irritant’ type receptors (9/80,11%). Nineteen pressure receptors were stimulated by positive transmural pressure, while only three stimulated by negative pressure. Nine drive receptors were also stimulated by positive pressure and inhibited by negative pressure. Such response to pressure was further evaluated by applying maintained pressures to the functionally isolated upper airway. These results are essentially consistent with findings obtained in the rabbit, but differ from those reported for the dog.

Laryngeal afferent activity and reflexes in the guinea pig

We have investigated the various sensory modalities represented in the laryngeal nerves of the guinea pig. In addition, we have examined the defensive responses to mechanical stimuli and capsaicin instillation into the laryngeal lumen of the same species. Recording from both the whole superior laryngeal nerve and from single units of the same nerve revealed the presence of afferent activity related (1) to the contraction of laryngeal muscles and/or the ‘tracheal tug’, (2) to transmural pressure changes, either positive or negative and (3) to mechanical and chemical irritants. The irritant type receptors of this species, when challenged with water solutions, show two distinct patterns of activation: some behave as osmoreceptors, some respond to the lack of chloride ions. Challenges with capsaicin solutions activated one ending with the characteristics of a C-fiber receptor that failed to respond to a subsequent trial. This behavior is consistent with the reflex apnea, dependent on an intact laryngeal innervation, induced by capsaicin instillation that was not elicitable on repeating the challenge. Cough to mechanical probing of the supraglottic area depended on an intact SLN, whereas cough elicited from the subglottic area depended on an intact RLN. Cough to mechanical stimulation could not be desensitized by capsaicin. These findings suggest the presence of two independent afferent pathways for defensive responses.

The Reliability of Endoscopic Examination in Assessment of Arytenoid Cartilage Movement in Horses Part I: Subjective and Objective Laryngeal Evaluation

Videorecordings of the laryngeal activity of 108 unsedated horses were obtained at rest by passing a flexible videoendoscope into the nasopharynx through the right ventral meatus. All videotaped images were reviewed once, and 72 were reviewed twice, by three veterinarians. Laryngeal cartilage movement was assessed subjectively with a five-tier grading system. The mean intraobserver agreement was 83.3% (range, 75.0%-90.2%) with a kappa statistic of .65 to .98. The mean interobserver agreement was 79.0% (range, 70.4%-80.6%) with a kappa statistic of .51 to .90. A computer program was developed to measure the left:right ratio of the rima glottidis. The mean left:right ratio for horses assigned a median laryngeal grade of I was 0.84 (range, 0.55-1.03); for grade II, 0.82 (0.50-1.12); for grade III, 0.59 (0.39-0.91); and for grade IV, 0.24 (0.07-0.35).

Vestibular and cerebellar modulation of expiratory motor activities in the cat.

1. The purpose of our investigation was to evaluate the hypothesis that components of the vestibular and cerebellar systems regulate efferent respiratory-modulated activities of cranial and spinal nerves. The hypothesis was based upon the observation that spinal neural activities during expiration are greatly altered subsequent to a change in posture. 2. In decerebrate and paralysed cats, efferent activities were recorded from the central cut ends of the phrenic nerve, intercostal nerve, branch of the intercostal nerve innervating the triangularis sterni, cranial iliohypogastric (abdominal) nerve and recurrent laryngeal nerve. 3. Animals were artificially ventilated. Those with intact vagi were ventilated by a servo-respirator which produced changes in lung volume in parallel with alterations in integrated activity of the phrenic nerve. Animals with bilateral vagotomy were ventilated with a standard respirator. 4. Aspiration of the entire cerebellar cortex did not produce alterations in levels of neural activities; the respiratory frequency was increased modestly. Following ablation of the ventrolateral portion of corpus medullare and cerebellar peduncles, expiratory activities of spinal nerves were completely eliminated whereas inspiratory activities were not greatly altered. Results were similar in animals having either intact or sectioned vagi. 5. Electrical stimulation or chemical stimulation by glutamate of regions of the ventrolateral cerebellum produced little change in respiratory neural activities except when these stimulations were within the infracerebellar nucleus. Stimulations in this nucleus caused pronounced increases in expiratory activities of spinal nerves. Neither inspiratory activities of spinal nerves nor inspiratory or expiratory activities of the recurrent laryngeal nerve were altered. Studies in animals having intact or sectioned vagi yielded similar results. 6. Bilateral lesions of neurons in the infracerebellar nucleus by injections of kainic acid in animals having intact or sectioned vagi caused an irreversible loss of expiratory activities of spinal nerves with neither inspiratory spinal activities nor inspiratory and expiratory laryngeal activities being altered. Similar findings were obtained following unilateral ablation of the infracerebellar nucleus in vagotomized cats. However, in cats with intact vagi, unilateral ablation of the infracerebellar nucleus produced only transient changes in either inspiratory or expiratory neural activities.(ABSTRACT TRUNCATED AT 400 WORDS)

The use of topical anesthetic in videostroboscopic examination of the larynx

Summary The use of topical anesthetic spray in the oropharynx to reduce excessive gag reflex and permit endoscopic videostroboscopy of the larynx is a common clinical practice. However, clinical observations and some studies have indicated that such use may alter physiological status and result in adverse changes in laryngeal activity. This study examined possible effects of topical anesthetic on a wide range of laryngeal activity assessed with videostroboscopy. Laryngeal activity of 10 young adults with normal larynges was evaluated with and without lidocaine. Results indicated that the use of topical anesthetic to reduce the gag reflex did not affect vocal performance and may have examination benefits

Involvement of bulbar respiratory and non-respiratory neurons in onset of expiration reflex

It was shown that excitation of high- and low-threshold superior laryngeal afferents triggers reflexes of varying complexity in a considerable proportion of non-respiratory neurons during experiments on cats anesthetized by Nembutal involving stimulation-induced expiration reflex. Systemic alterations in background firing activity were noted during this reflex in "respiratory" neurons; reflex reaction setting in as a result of low-threshold laryngeal afferent activation was also recorded in 22.4% of this group. Oligo- and polysynaptic excitatory connections were found between low-threshold laryngeal afferents and inspiratory beta neurons, P-cells, and laryngeal muscle motoneurons as opposed to inhibitory connections with inspiratory gammaneurons. This article discusses involvement of the neurons investigated in mechanisms of inspiratory inhibition, closure of the vocal chords, and adaptive decline in breathing rate occurring during expiration reflex.

Effects of preceding context on the voice-onset-time-category boundary.

The category boundary on a voice-onset-time (VOT) continuum ranging from bin to pin shifts when the stimuli are preceded by different carrier phrases. By using a variety of precursor phrases, by varying the temporal interval between precursor and test word, and by selectively eliminating either voicing information or spectral structure from the precursors, the present experiments show that the context effect is caused by the presence or absence of voicing in the precursor's final segment. The effect decreases with temporal separation but persists over several seconds. In addition, the "baseline" VOT boundary for isolated test words interspersed in a test sequence shifts depending on what precursor stimuli occur in the same sequence. The perception of VOT thus seems to be sensitive to both close and distant manifestations of laryngeal activity, always in an assimilative fashion, which suggests an integrative perceptual mechanism with a long time constant.

Risk factors and management of vocal cord hemorrhages: An experience with 44 cases

Summary Risk factors for vocal cord hemorrhages were reviewed in 44 professional voice users. In a majority of cases, the direct cause of hemorrhage was temporally related to singing, public speaking, or some form of forceful laryngeal activity. Sixteen of the 44 patients had a concomitant upper respiratory tract infection, and in the case of women patients, eight of 30 had hormonal imbalances. These included abnormal menstrual cycles, use of estrogen supplements, gynecological surgery, and the use of birth control pills. In most of these cases, correction of the underlying hormonal disturbance prevented the recurrence of bleeding episodes. We stress that such abnormalities should be ruled out by history and appropriate tests when necessary, to prevent the occasional crippling sequelae of vocal cord hemorrhages and review the various treatment options available for this condition.

Acoustic Measurements of Men’s and Women’s Voices

Several acoustic measures of laryngeal activity were made on adult speech to help answer two questions left unresolved by previous work: (1) how each measure varies, if at all, with phonetic structure, and (2) what aspect of laryngeal activity each measure specifies. Speech samples of 15 syllables (three vowels in five prevocalic consonantal contexts) were collected from men and women at two times of the day (early morning and late afternoon). Eight measurements were made, mainly on slices extracted from the middle of the vocalic portions, and inferential and correlational statistics were applied to these measures. Results of the inferential tests indicated differences between men and women in how laryngeal adjustments are made, affecting relative amounts of vocal jitter and spectral tilt of the voicing source. In addition, the voicing and manner characteristics of the prevocalic consonant were found to affect fundamental frequency, cycle-to-cycle perturbations, and amount of aspiration noise. To a lesser extent, vowel height and front/back tongue placement also affected these acoustic source characteristics. Results of the correlational tests showed that different laryngeal mechanisms contributed differentially to signal-to-noise ratios for men and women, and these mechanisms were more greatly affected by fundamental frequency for men's samples. Finally, various acoustic measures of laryngeal noise were found to be related to the same underlying mechanism.

Abductor vocal cord spasm

The purpose of this study is twofold. First, to introduce a new phenomenon--abductor vocal cord spasm, or abductor laryngospasm. Second, to reconcile a longstanding discrepancy involving the effect of lung inflation on vocal cord position. Abductor laryngospasm was induced in six anesthetized, tracheotomized dogs by the administration of continuous positive airway pressure (CPAP) after occlusion of the trachea for 60 seconds. Abductor laryngospasm was characterized by sustained vocal cord abduction with concomitant massive, continuous posterior cricoarytenoid muscle (PCA) electromyography (EMG) activity and little or no laryngeal adductor muscle EMG activity. Vocal cord opening was sustained for up to 90 seconds. In the same dogs, administration of CPAP, after hyperventilation of the animal, resulted in adductor laryngospasm. Adductor laryngospasm was characterized by steady apposition of the vocal cords, massive laryngeal adductor muscle EMG activity, and silent PCA EMG activity. Abductor laryngospasm appears to be the physiologic converse of adductor laryngospasm. The results of this study show that lung inflation can produce either vocal cord abduction or adduction, depending on whether the dog is hypoventilated or hyperventilated before administration of CPAP.

Drug induced depression of laryngeal reflex activity: A comparison of codeine and a new opioid, tramadol

Drug induced depression of laryngeal reflex activity: A comparison of codeine and a new opioid, tramadol

Nasometric and Phototransductive Measurements of Reaction Times Among Normal Adult Speakers

The temporal relationship among laryngeal, velopharyngeal, and labial activity was investigated by studying the reaction times of eight normal adults. Four female and four male subjects sustained production of the nasal consonant /m/ until a computer-driven imperative tone was presented at which time they were required to say /pi/ as quickly as possible. This task was repeated 30 times for each subject. The offset of voicing at the end of the /m/ and the onset of bilabial plosive release were monitored using a commercially available Nasometer. The onset of velopharyngeal (V-P) movement toward closure and the attainment of closure were monitored using a photodetector system. Across 240 responses, the average latencies were: 146 ms for initiation of V-P movement toward closure, 224 ms for voicing offset, 280 ms for onset of V-P closure and 317 ms for onset of plosive release. The significance of these findings is discussed with respect to speech motor control and the clinical evaluation of patients with velopharyngeal impairments.

Remote and local effects of stress within and among articulatory subsystems

Previous research on stress has focused almost exclusively on articulatory correlates local to a single target syllable within a single articulatory subsystem (e.g., the lip‐jaw or the respiratory system). However, the articulatory correlates of stress are not local in either sense. Although a few studies report remote effects of stress (effects not confined to the stressed segment) on the speech acoustics, articulatory studies have reported the effects of stress only for single subsystems (e.g., oral, laryngeal, and respiratory); there have been no systematic investigations of the extent to which stress effects are manifest throughout the speech production system. The present study investigates the effects of stress in the vocal tract and respiratory system. Lip and jaw and respiratory kinematics, laryngeal vibration, and intra oral air pressure were simultaneously recorded during recitation of sentences in which lexical, contrastive, or sentential (focus) stress were varied. Changes in the articulatory kinematics and in the relative timing of laryngeal, respiratory, and supralaryngeal activity are analyzed as a function of stress type and position in the utterance. Results suggest that the articulatory correlates of stress are distributed continuously within and across subsystems. [Work supported by NIH.]

Influence of lung volume on activities of branches of the recurrent laryngeal nerve.

To investigate the influence of inspiratory lung inflation on the respiratory activities of laryngeal motor nerves, vagally intact decerebrate paralyzed cats were ventilated by a servorespirator in accordance with their own phrenic nerve activity. Records were made of the activities of the phrenic nerve, the superior laryngeal nerve (SLN), the recurrent laryngeal nerve (RLN), and the intralaryngeal branches of the RLN serving the thyroarytenoid (TA) and posterior cricoarytenoid (PCA) muscles. Neural activities were assessed in the steady state at different end-tidal O2 and CO2 concentrations. Transient responses to withholding inspiratory lung inflation and to preventing expiratory lung emptying were also studied. Hypercapnia and hypoxia increased the inspiratory activities of the phrenic nerve, SLN, RLN, and its PCA branch. TA inspiratory activity was not changed. Expiratory activities of RLN, PCA, and TA were all increased in hypoxia. When lung inflation was withheld, neural inspiratory duration and the inspiratory activities of all nerves increased. The subsequent period of neural expiration was marked by an exaggerated burst of activity by the TA branch of the RLN. TA expiratory activity was also sharply increased after inspiratory efforts that were reflexly delayed by the prevention of lung emptying. TA activity in expiration was enhanced after vagotomy and was usually more prominent than when lung inflation was withheld before vagal section. The results demonstrate the importance and complexity of the influence of vagal afferents on laryngeal motor activity.

Acoustic and physiological reaction times of stutterers and nonstutterers.

This study investigates reaction times in the fluent speech utterances of stutterers and nonstutterers under several experimental conditions. Twenty adult stutterers and twenty matched controls produced utterances of three lengths--one syllable words, polysyllabic words, and sentences--in two conditions of time pressure (high and low) and two conditions of preparation (delayed and immediate responding) in a reaction-time paradigm. Recordings were made of EMG signals from the orbicularis oris inferior and from the extrinsic laryngeal area, as well as electroglottographic and acoustic signals. Measures were made of the duration of intervals between the stimulus, the acoustical onset of voicing, the onset of laryngeal EMG activity, and the onset of lip EMG activity. The durations of subintervals between the stimulus, the three physiological signals, and the acoustic signal were also measured. The results suggest that the reaction times of stutterers and nonstutterers are both increased by longer utterances, and that the effect is proportionally greater for the stutterers. The requirement to respond with minimal preparation produced longer reaction times in both groups, particularly for longer utterances, but this finding was stronger for stutterers than for nonstutterers, particularly in the prelaryngeal subintervals. The high time-pressure condition produced an unusual pattern of responding in many subjects. The analysis of subintervals indicated that the additional time taken by stutterers in responding was located in the earlier parts of the response, particularly when the utterances were longer. The results are interpreted as suggesting that stutterers may have difficulty in the motor programming of speech behavior.

Laryngeal brain stem evoked response.

Sensory stimuli to the larynx evoke a laryngeal adductor reflex mediated by the brain stem via superior and recurrent laryngeal nerves. Aberrant laryngeal reflexes have been proposed to explain a number of poorly understood disorders, including "reflex apnea," idiopathic laryngospasm, and sudden infant death syndrome. The purpose of the present study was to evaluate far field brain stem recordings following stimulation of the superior laryngeal nerve to determine whether laryngeal brain stem response is a valid measure of laryngeal activity at the brain stem level. The nerve was stimulated electrically in adult cats, and the resultant laryngeal adductor response as well as far field brain stem activity was recorded. For the latter, six reproducible positive and five reproducible negative waves were obtained via posterior pharyngeal (+) and posterior cervical (-) recording electrodes. Response threshold and latencies were measured and evaluated as a function of stimulus parameters. Wave latencies corresponded closely to those reported in prior near and far field evoked response recordings.

Regulation of respiratory motor outflow to the larynx and diaphragm by GABA receptors

Effects of intracisternal administration of the γ-aminobutyric acid receptor agonist, muscimol, on recurrent laryngeal and phrenic nerve activities were assessed in the cat. Muscimol (0.1–2.4 μg) produced a dose-related inhibition of the respiratory activity in both of these nerves. The inhibition was seen as a decrease in the amplitude of nerve activity with no significant change in respiratory rate. The ED 50 values for muscimol and its 95% confidence interval for inhibition of the inspiratory activity in the recurrent laryngeal and phrenic nerves were 0.22 μg (0.17–0.29) and 0.27 μg (0.19–0.38), respectively. The potency of muscimol for inhibition of these nerve activities was not significantly different. Expiratory activity in the recurrent laryngeal nerve was completely inhibited prior to either the inspiratory activity in this nerve or in the phrenic nerve. Intracisternal administration of the γ-aminobutyric acid receptor antagonist, bicuculline, rapidly reversed the inhibition in both n erves. Reversal times for inhibition of the inspiratory activities in the recurrent laryngeal and phrenic nerves were not significantly different. Return of inspiratory activity in each nerve always preceded the return of expiratory activity in the recurrent laryngeal nerve. These results demonstrate that CNS γ-aminobutyric acid receptors are involved in the regulation of respiratory motor outflow to the larynx as well as the diaphragm.

Posterior cricoarytenoid and diaphragm activities during tidal breathing in neonates.

To investigate airflow regulation in newborn infants, we recorded airflow, volume, diaphragm (Di), and laryngeal electromyogram (EMG) during spontaneous breathing in eight supine unsedated sleeping full-term neonates. Using an esophageal catheter electrode, we recorded phasic respiratory activity consistent with that of the principal laryngeal abductors, the posterior cricoarytenoids (PCA). Sequential activation of PCA and Di preceded inspiration. PCA activity typically peaked early in inspiration followed by either a decrescendo or tonic EMG activity of variable amplitude during expiration. Expiratory airflow retardation, or braking, accompanied by expiratory prolongation and reduced ventilation, was commonly observed. In some subjects we observed a time interval between PCA onset and a sudden increase in expiratory airflow just before inspiration, suggesting that release of the brake involved an abrupt loss of antagonistic adductor activity. Our findings suggest that airflow in newborn infants is controlled throughout the breathing cycle by the coordinated action of the Di and the reciprocal action of PCA and laryngeal adductor activities. We conclude that braking mechanisms in infants interact with vagal reflex mechanisms that modulate respiratory cycle timing to influence both the dynamic maintenance of end-expiratory lung volume and ventilation.