Glottic Aperture Research Articles

Effect of hypercapnia and hypoxia on arytenoideus muscle activity in normal adult humans.

The electrical activity of the arytenoideus muscle, a vocal cord adductor, was measured in 14 normal adult humans during progressive isocapnic hypoxia and progressive hyperoxic hypercapnia. Electromyograms of the arytenoideus were obtained with intramuscular hooked-wire electrodes implanted by means of a fiber-optic nasopharyngoscope. Correct placement of the electrodes was confirmed by discharge patterns during voluntary maneuvers. In three of the subjects, respiratory-related arytenoideus activity was not present during quiet breathing or chemical stimulation. During quiet breathing in the 11 other subjects, the arytenoideus exhibited phasic activity during expiration and usually tonic activity throughout the respiratory cycle. Phasic and tonic arytenoideus activity decreased under hypoxic and hypercapnic conditions. At higher levels of chemical stimulation in many subjects, short abrupt bursts of activity were frequently present at the transitions between inspiration and expiration. To determine the mechanical effect of the latter electromyographic findings, arytenoideus activity and fiber-optic images of the glottic aperture were simultaneously recorded in nine additional normal adult human subjects during progressive hyperoxic hypercapnia. The short abrupt bursts of arytenoideus activity were usually associated with a decrease in glottic aperture, although no change and an increase in glottic aperture were observed in individual subjects. The results suggest that the arytenoideus muscle may have an important role in the control of ventilation in normal human subjects.

Laryngeal response to passively induced hypocapnia during NREM sleep in normal adult humans.

Passively induced hypocapnia in animals activates vocal cord adductor muscles and decreases the glottic aperture. The purpose of this study was to determine if passively induced hypocapnia has similar effects in normal adult humans in stage 3/4 non-rapid-eye-movement (NREM) sleep. Hypocapnia was induced by hyperventilating the subjects with a positive-pressure ventilator via a nose mask. At hypocapnic levels below the CO2 apneic threshold, abrupt cessation of mechanical ventilation was followed by an apnea. In protocol 1, intramuscular electromyographic recordings of intrinsic laryngeal muscles were obtained in nine subjects. Activity of the posterior cricoarytenoid muscle, a vocal cord abductor, disappeared during passive hyperventilation. The muscle remained electrically silent during an apnea, but phasic inspiratory activity reappeared with the first respiratory effort. The thyroarytenoid and arytenoideus muscles, both vocal cord adductors, were electrically silent during spontaneous breathing in NREM sleep. Hypocapnia was frequently associated with activation of both adductor muscles. Once activated, the adductor muscles remained tonically active during an ensuring apnea. In protocol 2, a fiber-optic scope was advanced transnasally into the hypopharynx to determine glottic aperture size during passively induced hypocapnic apnea. In the seven subjects who achieved stable NREM sleep, the glottic aperture during an apnea was smaller than at any time throughout the respiratory cycle during spontaneous breathing just before positive-pressure ventilation. The results suggest that the decrease in glottic aperture observed during an induced hypocapnic apnea is due to suppression of the posterior cricoarytenoid muscle and/or activation of vocal cord adductor muscles.

Changes in voice-onset time in speakers with cochlear implants

Voice-onset time (VOT) was measured for the English plosives in /Copen aye/ context spoken by three female and one male postlingually deafened recipients of multi-channel (Ineraid) cochlear implants. Recordings were made of their speech before activation of their speech processors and at intervals after activation, extending over several years. Also measured were: instantaneous oral airflow; sound pressure level; an indirect index of glottal aperture; and average airflow during passage readings. Pre-implant, all four speakers characteristically uttered plosives with too-short VOT, compared to normative data. After activation of their processors, all four were relatively accurate in identifying plosives with respect to voicing, and the three female speakers lengthened VOT. The women also increased glottal aperture post-activation. However, none of the women increased peak oral flow following plosive release, possibly because of a countervailing decrease in subglottal pressure: all three reduced SPL post-activation. Complementary results were found for the male speaker: a decrease in inferred glottal aperture and an increase in oral flow accompanied by an increase in SPL. Increases in glottal aperture are expected to inhibit the onset of voicing in the plosives [K. Stevens, Phonetica 34, 264–279 (1977)]. Consequently, some or all of the observed increases in VOT with activation of the implant processors may be due to ‘‘postural’’ adjustments of the larynx. [Work supported by N.I.D.C.D.]

Phonation threshold pressure in a physical model of the vocal folds

A physical model of a vocal fold was constructed with three layers: an artificial epithelium (latex), a superficial Reinke’s space (water), and an immobile vocal fold body (aluminum). This vocal fold was positioned in a plexiglas airway such that the glottal aperture and the convergence angle could be varied systematically with respect to a solid boundary, which represented the opposite vocal fold in a hemilarynx configuration. Subglottal pressure was controlled with a constant pressure valving system. Phonation threshold pressure (the Hopf bifurcation in nonlinear dynamics) was measured as a function of glottal aperture and divergence angle. This pressure increases with increased aperture and convergence, as predicted by theory, but results for a divergent glottis are not as easy to interpret. [This research was supported by Grant No. P60 DC00976 from the National Institute on Deafness and Other Communication Disorders.]

Physiologic Assessment of Arytenoid Adduction

Arytenoid adduction as described by Isshiki is a surgical technique used to improve vocal quality by adducting the arytenoid cartilage of a paralyzed vocal fold, medializing the fold, and closing the posterior glottic aperture. Surgical results of this operation were evaluated by preoperative and postoperative voice recordings, laryngoscopy, and stroboscopy. Objective measurements of vocal jitter, shimmer, and signal to noise ratio were done to assess changes in the vibratory patterns, and analysis of data from 12 patients revealed improved glottic function postoperatively. Often an anterior medialization procedure, primarily a type I thyroplasty, was used to supplement the posterior medialization achieved by adduction of the arytenoid. Arytenoid adduction is recommended as an effective and reliable treatment for posterior glottic insufficiency.

Within-breath variations of forced oscillation resistance in healthy subjects

Respiratory resistance (Rrs) was measured by the forced oscillation technique at 10, 20 and 30 Hz in 54 healthy subjects. The sinusoidal pressure oscillations were applied around the head, rather than at the mouth, so as to minimize transmural pressure across extrathoracic airway walls and the corresponding artefact (Peslin et al., J Appl Physiol, 1985, 59, 1790-1795). The flow (V') and volume (V) dependences of Rrs during the respiratory cycle were analysed by least square regression according to: Rrs = K1 + 2.K2.[V']#- K3.V, where K1 and K2 are Rohrer's constants, and where K3 expresses the (negative) volume dependence of Rrs. The analysis was made separately on the inspiratory and expiratory phases. A good fit was usually found between the data and the model, with a root-mean-square error averaging 15% of the mean Rrs at 10 Hz. At all frequencies K2 and K3 were substantially and significantly larger, and K1 slightly lower during expiration than during inspiration. Rrs, K1 and K3 were minimum at 20 Hz, while K2 exhibited a strong positive frequency dependence. The decrease of Rrs from 10 to 20 Hz was entirely explained by the variations of its linear component, and its increase from 20 to 30 Hz was largely due to its flow dependent component. Both the phasic variations and the frequency dependence of the coefficients suggest that the model is purely descriptive and that coefficients K2 and K3 reflect a number of phenomena, including the variations in glottic aperture during the respiratory cycle.

Posterior cricoarytenoid activity and glottic size during hyperpnea in humans

We measured the electromyographic activity of the posterior cricoarytenoid (PCA) muscle simultaneously with glottic width (dg) in five normal human subjects during hyperpnea induced by hypoxia (7% CO2 in N2) or hypercapnia (9% CO2 in 50% O2). The glottic aperture was measured during inspiration at the time corresponding to peak inspiratory PCA activity and during expiration at the time corresponding to the minimum tonic activity. During hyperpnea, peak and tonic PCA activity increased simultaneously with widening of the vocal cords in both phases of the respiratory cycle. The PCA activity during both inspiration and expiration showed a single curvilinear relationship with dg of the form dg = A - Be-k.PCA (where A, B, and k are constants) in three of the five subjects. At 50% of maximum PCA activity, dg already reached 95% of its maximum value, which was less than that recorded during a voluntary forced expiratory maneuver. The single curvilinear relationship between PCA activity and dg could be due to the length-tension relationship of the PCA muscle and/or changes in its mechanical coupling, as well as simultaneous agonist and antagonist laryngeal muscle activity during progressive chemical stimulation. Also, further widening of the glottis during forced expiration suggests recruitment of additional muscles, e.g., the arytenoideus.

Regulation of Phonatory Efficiency by Vocal Fold Tension and Glottic Width in the Excised Canine Larynx

An excised canine larynx was used to assess the effects of glottic width and vocal fold tension on acoustic power, aerodynamic power, and vocal efficiency. Multiple regression analysis of the data obtained from 10 larynges revealed that with increased vocal fold tension there is a logarithmic decline in radiated acoustic power, while aerodynamic power remains constant (p less than .05). Vocal efficiency has a similar logarithmic decrease with increased tension (p less than .05). With narrowing of the glottis, the acoustic power increases more than the aerodynamic power delivered to the larynx, and the efficiency increases. The inverse relationships glottic width has with acoustic power and vocal efficiency are best described by a reciprocal model (p less than .01). There is a negative linear relationship between glottic width and aerodynamic power. These results suggest that within the larynx the energy conversion is regulated by glottic aperture and longitudinal vocal fold tension. The optimal width for efficiency appears to be the narrowest width that produces phonation within the modal register, whereas increased tension decreases the efficiency of the glottis.

Thyroarytenoid muscle activity during loaded and nonloaded breathing in adult humans

Previous fiber-optic studies in humans have demonstrated narrowing of the glottic aperture in expiration during application of expiratory resistive loads. Nine healthy subjects were studied to determine the effect of expiratory resistive loads on the electromyographic activity of the thyroarytenoid (TA) muscle, a vocal cord adductor. Four of the nine subjects also underwent the application of inspiratory resistive loads and voluntary prolongation of either inspiratory (TI) or expiratory (TE) time. TA activity was recorded by intramuscular hooked-wire electrodes. During quiet breathing in all subjects, the TA was phasically active on expiration and often tonically active throughout the respiratory cycle. TA expiratory activity progressively increased with increasing levels of expiratory load. Inspiratory loads resulted in increased TA "inspiratory" activity. Voluntary prolongation of TE to times similar to those reached during loaded breathing induced increases in TA expiratory activity similar to those reached during the loaded state. Voluntary prolongation of TI was associated with an increase in TA inspiratory activity. Similar increases in TI during inspiratory loading or voluntary conditions were associated with comparable increases in TA inspiratory activity in three of the four subjects. In conclusion, increased activation of TA during the application of expiratory resistive loads implies that the reported narrowing of glottic aperture during expiratory loading is an active phenomenon. Changes in activation of the TA with resistive loads appear to be related to changes in respiratory pattern.

Valeur comparée des signes cliniques d'intubation difficile chez la femme

A prospective study was designed to compare the value of clinical signs aimed to predict difficult intubation in women. A group of 663 women, scheduled for elective surgery, were assessed by an anaesthetist at the preanaesthetic visit. Following parameters were assessed : the degree of mouth opening, the chin-hyoid bone and the chin-thyroid cartilage distances, dental and facial abnormalities, age, weight. All patients were ranked on the Mallampati scale. Another anaesthetist carried out the anaesthetic induction and endotracheal intubation. The latter was deemed to have been difficult if special procedures had been required (use of a stylet, a fibroscope, or Sellick's manœuvre). In accordance with these criteria 12.5 % of women were difficult to intubate. Furthermore, he assessed the degree of glottic exposure, using a Macintosh blade and according to Cormack's classification. Six per cent of women were ranked C or D in Cormack's classification (C : the glottic aperture was not seen ; D : the epiglottis was not seen). Finally 66 % of women with difficult intubation and 84 % of those with severely abnormal glottic exposure were ranked > 1 on the Mallampati scale. This scale had high sensitivity (0.84), but a specificity of only 0.66. Other clinical criteria (mouth opening, the chin-hyoid bone distance) had a lower sensitivities, but seemed more specific. Multivariate analysis showed that specificity could be improved (0.84) if the distance between the upper and lower incisor teeth (mouth opening) was associated with Mallampati's rank, without any loss in sensitivity. A simple chart is proposed to assess the risk of difficult intubation.

Laryngeal Changes during Exercise and Exercise-Induced Asthma

Exercise-induced asthma is defined as bronchospasm within the distal airways initiated by exercise. Whether the larynx responds to produce an exacerbation or alleviation of symptoms during an attack has never been evaluated. Thirty subjects were tested, including 15 normals and 15 with exercise-induced asthma. Laryngeal response to exercise was determined by measuring the area of the glottic aperture before, during, and after exercise. The glottis was visualized with a flexible laryngoscope and video images were recorded during monitoring of respirations. Asthma was induced in subjects by having them exercise on an ergometer for 10 minutes while breathing dry air at 10 degrees C. Measurements were subsequently made from recorded images and relative glottic areas were compared between groups. Our data quantify the normal physiologic response of the larynx to exercise and demonstrate a substantial laryngeal contribution to asthma induced by exercise.

Glottic dimensions in healthy men and women

Glottic aperture is important in modulating respiratory system resistance. Male patients with obstructive sleep apnea (OSA) have a smaller glottic cross-sectional area compared to controls. Since OSA has a strong male predominance, we reasoned that glottic dimensions may differ between healthy men and women. Therefore, we utilized the acoustic reflection to measure glottic cross-sectional area in 44 non-smoking, non-obese, healthy subjects, 25 men and 19 women. Glottic area was measured during a continuous slow expiration from total lung capacity (TLC) to residual volume (RV). We compared glottic areas in men and women at three lung volume: TLC, 50% of vital capacity (VC), and RV. We found that in all but 2 subjects, glottic areas at TLC was greater than at 50% VC or RV. At any given lung volume, there was no significant difference in glottic area between men and women. The reduction in glottic area between TLC and RV was also similar between men and women (36 ± 24% and 33 ± 21%, respectively). However, this reduction in glottic area occurred mainly at low lung volumes in women, and more uniformly throughout the vital capacity range in men. We conclude that changes in glottic dimensions are dependent on lung volume, that healthy men and women have similar glottic areas, and that the glottic aperture shows similar variation with lung volume among both sexes.

Expiratory glottic widening in asthmatic subjects during exercise-induced bronchoconstriction.

Glottic caliber is modulated in a way that optimizes the airway resistance and the work of breathing. The midexpiratory glottic narrowing that normally occurs during tidal breathing is enhanced during histamine- or methacholine-induced airway narrowing. Exercise is associated with increased ventilatory demand and midexpiratory glottic widening in healthy subjects. However, the relative contribution of glottic aperture to airflow limitation during exercise-induced asthma is unknown. Consequently, we used the acoustic reflection technique to test whether a decrease in midexpiratory glottic size occurred also during exercise-induced bronchoconstriction in seven asthmatic subjects. Exercise resulted in a 38 +/- 16% (SD) fall in FEV1 from the baseline value (p less than 0.001) and a significant increase in midexpiratory glottic cross-sectional area from 1.89 +/- 0.45 cm2 before to 2.36 +/- 0.71 cm2 during bronchoconstriction (p less than 0.05). This midexpiratory glottic widening was also associated with increased tidal flow rates. We conclude that in marked contrast to airway obstruction induced by histamine or methacholine, exercise-induced asthma is associated with midexpiratory glottic widening, which occurs concomitantly with a decrease in lower airway caliber. We suggest that modulation of glottic aperture during acute asthma is heterogeneous and depends partly on the initiating stimulus.

Laryngeal Electrode Platform: An Indwelling Device for Mobilizing the Vocal Cords

By passing electrical current across the laryngeal mucosa and esophageal wall, the recurrent laryngeal nerve can be stimulated, thereby mobilizing the vocal cords. In designing a device that would utilize this phenomenon, we theorized that stability, targeting, and mucosal contact could be maximized by an indwelling device that would conform precisely to the topography of the posterior larynx. In five dogs, molds of the hypopharynx and proximal esophagus were fashioned in vivo by injection of an alginate compound. From each mold was constructed a vinyl platform blanketed with electrodes. Each platform fit snugly in place, and could activate the nerve consistently in any of the dogs. With as little as 3 mA pulsatile current, use of specific electrodes enabled bilateral abduction, more than doubling the resting glottic aperture. Bilateral adduction was sometimes attainable. Such a platform may have use in visualizing subglottic lesions, diagnosing laryngeal movement disorders, and facilitating intubation and extubation.

Transcutaneous electrical stimulation of the recurrent laryngeal nerve in monkeys.

The recurrent laryngeal nerve (RLN) of four anesthetized adult Macaca fascicularis monkeys was stimulated by applying current with blunt electrodes placed unilaterally and bilaterally on the intact neck skin along the tracheoesophageal groove. The stimulus consisted of 2.5- to 4.0-mA cathodal pulses, each of 1-ms duration, beginning at a frequency of 10 Hz and increasing by 10-Hz increments to 100 Hz. Unilateral stimulation from 10 to 30 Hz resulted in a graded vocal cord abduction, with the maximal glottic aperture occurring at 30 Hz. Stimulation above 30 Hz produced a graded cord adduction, with nearly complete glottic closure at 100 Hz; bilateral stimulation yielded similar results, with total glottic closure at 100 Hz. Confirmation of the RLN as mediator of this frequency-dependent cord motion was achieved by surgically isolating it and attaining identical results with direct stimulation. No cardiopulmonary alterations were observed in any trial. Transcutaneous electrical stimulation of the RLN seems to be a relatively safe, reliable, and noninvasive method of controlling vocal cord position and thereby the glottic airway in monkeys.

Oscillation threshold conditions in phonation

A small‐oscillation theory is developed for determining threshold conditions for onset and release of vocal fold vibration as a function of lung pressure, tissue viscosity, glottal aperture, and surface wave velocity in the mucosa (vocal fold cover). It is found that oscillation threshold lung pressure increases in proportion to mucosal wave velocity. In other words, phonation initiates at lower pressures (less effort) if the vocal fold cover is lax and propagates slow surface waves. Experimental evidence on excised dog larynges confirms that a stiffer cover (at greater vocal fold lengths) requires greater lung pressure. The theoretical prediction that increased glottal aperture (spreading of the vocal folds, as in breathy voice) also increases the oscillation threshold lung pressure has been more difficult to verify experimentally, but increased tissue viscosity produces an observable increase. Applications to phonetics and voice care are cited. [Work supported by NINCDS.]

Transcutaneous electrical stimulation of the recurrent laryngeal nerve: a method of controlling vocal cord position.

This study was designed to examine the feasibility of transcutaneous stimulation of the recurrent laryngeal nerve. Electrical activation of the recurrent laryngeal nerve was achieved by applying a blunt electrode to the intact neck skin at specific points along the tracheoesophageal groove in anesthetized adult dogs. The stimulus consisted of 10 mA cathodal pulses, each of 1 msec duration, delivered at a frequency of 10 Hz and increased by 10 Hz increments up to 100 Hz. Vocal cord excursion was directly related to the frequency of applied current. In all six dogs studies, stimulation at 30 Hz resulted in maximal ipsilateral vocal cord abduction, while stimulation at frequencies greater than 40 Hz resulted in ipsilateral vocal cord adduction up to or across the midline. Vocal cord movement was immediate and persisted for the duration of the stimulus train. Surrounding neck muscles were not visibly activated. We propose that the observed frequency-dependent movement of the vocal cords occurred because of the difference between the contraction times of the intrinsic abductor and adductor muscles of the larynx. Transcutaneous recurrent laryngeal nerve stimulation appears promising, both as a diagnostic aid in laryngoscopy and as a therapeutic tool in controlling the glottic aperture.

Respiratory effects of chronic intrathoracic vagotomy in rabbits.

Respiratory variables were recorded in 29 anaesthetized, chronic rabbits after bilateral vagotomy in the chest. The Hering-Breuer reflex was absent. Their breathing frequency was lowered and they became hypoxaemic compared to prevagotomy values. Movements of the vocal cords remained undisturbed and the laryngeal resistances were similar to those in the group of intact rabbits. Laryngeal palsy after midcervical vagotomy in these rabbits increased the tracheal pressures to lower values than in the group of intact, acutely vagotomized rabbits. This demonstrates the less adducted position of the paralyzed vocal cords due to the sequence of denervation steps and consequent glottal aperture proportional to increased respiratory airflow.

Restoration of the airway following bilateral recurrent laryngeal nerve paralysis.

Bilateral recurrent laryngeal nerve paralysis has been treated by a number of ingenious techniques that include arytenoidectomies, vocal cord lateralizations, cordectomies, and, recently, reinnervation procedures and laser arytenoidectomies. An arytenoidectomy is recommended by a thyrotomy approach without lateralization of the vocal cord. The resulting airway is adequate for decannulation by expansion of the posterior glottic aperture, with preservation of the anterior glottis for phonation.

Laryngeal muscle recovery after suxamethonium. Detection during intratracheal jet ventilation by pressure curve monitoring.

Complications due to intratracheal jet ventilation are often caused by the unrecognized recovery of laryngeal muscles. The rate of rise of pressure in a main bronchus alters with changes of the glottic aperture during jet ventilation. The special pressure curve monitor sets off an alarm when the steepness of the rising curve changes. During recovery these alarms, as well as the onset of phonation, coughing, spontaneous breathing and forearm muscle activity are recorded simultaneously. Forearm muscle activity always appears later than the alarm, and often later than the other recorded phenomena. Pressure curve monitoring provides advance warning of returning muscle activity in the larynx, but conventional muscle activity monitoring in the forearm does not.