Thyroid cartilage movements during breathing

We measured lateral (outward) thyroid cartilage displacement (TCD) of the larynx in six supine anesthetized (intravenous chloralose) dogs. Combined left and right TCDs were measured with linear transducers attached by a thread to the thyroid alae. During tidal breathing via a tracheostomy, phasic inspiratory TCD occurred in all dogs [0.66 +/- 0.2 mm (mean +/- SE)] together with phasic inspiratory electromyographic activity in the cricothyroid (CT) and posterior cricoarytenoid (PCA) muscles. During brief tracheal occlusions, TCD increased significantly to 1.27 +/- 0.2 mm (P = 0.001), accompanied by an increase of 95-115% in the peak CT and PCA electromyograms. Bilateral supramaximal electrical stimulation of the external branches of the superior laryngeal nerve (ExSLN) produced a TCD of 9.9 +/- 0.8 mm; however, similar stimulation of the recurrent laryngeal nerve (RLN) produced a TCD of only 1.33 +/- 0.1 mm (P = 0.0001). Furthermore, bilateral section of the ExSLN in five dogs significantly reduced tidal TCD by 48.7 +/- 24.4% (P < 0.05), and bilateral section of both the ExSLN and RLN resulted in slight phasic inward TCD (-0.06 +/- 0.05 mm). Thus, it appears that the activities of both the CT and RLN-innervated muscles (probably the PCA muscle) contribute to tidal breathing TCD. These findings suggest that inspiratory dilation of the hypopharynx is mediated by contractions of CT and PCA muscles.

Assessment of patient position for fiberoptic intubation using videolaryngoscopy

STUDY OBJECTIVE

To compare laryngoscopic appearance obtained during flexible fiberoptic laryngoscopy with the patient's atlanto-occipital joint in the neutral and extended positions.

DESIGN

Controlled clinical trial with each patient (in the neutral position) acting as his or her own control.

SETTING

University teaching hospital.

PATIENTS

20 adult ASA physical status I and II patients, without anatomical airway abnormalities, undergoing elective surgical procedures.

INTERVENTIONS

Fiberoptic laryngoscopy was performed on each patient with his or her atlanto-occipital joint in the neutral and extended positions.

MEASUREMENTS AND MAIN RESULTS

Photographs of the laryngoscopic appearances were graded on a scale of 1 to 4 by a blinded observer according to the proportion of the laryngeal inlet visible. Atlanto-occipital extension improved laryngoscopic appearance in 14 cases and produced no change in the remaining 6.

CONCLUSION

Atlanto-occipital extension is a useful maneuver during attempted fiberoptic intubation.

[Functionally determined area changes in the oro-pharyngo-laryngeal vocal tract of singers as shown by magnetic resonance tomography]

The oro-pharyngeal-laryngeal resonating spaces were studied in 12 singers at varying stages of their training by means of medio-sagittal MRI images, and the results were compared. The singers were requested to sing /a/ /u/ and /i/ at various pitches and with increasing loudness. The total oro-pharyngo-laryngeal areas were integrated by means of the MRI sections. The relationship between the oro-pharyngeal and pharyngo-laryngeal areas was determined, as well as their ratio to total area. With increasing volume there was increase in the area of the oro-pharyngeal component with no change in the pharyngo-laryngeal component. The relationship of the partial areas depends on the extent of training of the singer.

The laryngeal mask airway for dental surgery--a review

The ideal airway requirements for oral surgery are the provision of a stable, unobstructed airway, protection of the lungs from aspiration, minimal interference with the surgical field and a low complication rate. Neither the nasal mask nor endotracheal tube meet these requirements. The laryngeal mask airway (LMA), provides a third type of airway for consideration in oral surgery that offers some of the benefits of intubation and avoids many of the associated hazards. It can be inserted without use of a laryngoscope or muscle relaxants, and is designed to produce an airtight seal around the laryngeal inlet. It provides a secure airway suitable for spontaneous or controlled ventilation and acts as an airtight throat pack. Scavenging of waste gases is possible, and it is well tolerated during recovery. A modification, specifically designed for head, neck and dental anaesthesia, has recently become available. The purpose of this article is to provide a brief overview of the LMA with special emphasis on its use in oral surgery.

Laryngotracheal anatomy and physiology

Thorough knowledge of the laryngotracheal anatomy and physiology is a prerequisite for understanding the pathophysiology and for an adequate treatment of patients with anomalies, stenoses and other pathology in this area. The larynx is part of the upper respiratory tract, our voice organ and it prevents the passage of secretion and food to the lower airways. Anatomical differences between adults and children, males and females are important to consider, as the size of the structures underlies the decision for the size of tubes and cannulas to be used. Knowledge of the muscles and mucosa is important in augmentation, e.g. in phono-surgery and for procedures in patients with laryngeal palsy. The trachea with its location causes specific problems in the treatment of stenoses and tumours. The mucociliary system is nowadays being more focused upon.

Morphometry of the larynx in horizontal sections

PURPOSE

Until recently, only few studies on laryngeal morphometry in the horizontal plane, which used unreliable techniques, have been reported. The established methods of whole-organ serial sectioning of the larynx serve the purpose of histological investigation very well. Because they cause major tissue shrinkage, these techniques are not useful for morphometry. Nevertheless, normal data of laryngeal horizontal anatomy are of great surgical and diagnostic interest. Data on endolaryngeal angles, airway lumina, and the thickness of parts of the laryngeal skeleton can be helpful in the planning of endolaryngeal surgical intervention or the transcutaneous placement of electrodes for laryngeal electromyography. The aim of this study was to establish a method for the production of whole-organ serial sections that allows for the collection of exact and reliable morphometrical data.

MATERIALS AND METHODS

A total of 20 fresh human cadaver larynges were investigated in this study. Nineteen measurements on three different planes were obtained in each larynx. The larynges were shock-frosted using liquid propane and nitrogen and then cut with a slicing machine. Measurements were obtained using a computer-aided analyzing system.

RESULTS

The collected data give an exact and extensive description of the morphometrics of laryngeal structures such as thyroid and cricoid cartilage, arytenoid cartilages, vocal cords, and endolaryngeal airways at different section levels.

CONCLUSION

This study is the first to provide detailed anthropometric data on whole-organ sections of the larynx following a new method. This technique of using serial sections of the investigated specimen avoids artifacts caused by tissue fixation. Thus, it may be considered being particularly suited to the conduction of anthropometric studies on human larynges.

Topographical relations between the posterior cricothyroid ligament and the inferior laryngeal nerve

The posterior cricothyroid ligament and its topographic relation to the inferior laryngeal nerve were studied in 54 human adult male and female larynges. Fourteen specimens were impregnated with curable polymers and cut into 600-800 microns sections along different planes. Forty formalin-fixed hemi-larynges were dissected and various measurements were made. The posterior cricothyroid ligament provides a dorsal strengthening for the joint capsule of the cricothyroid joint. Its fibers spread in a fan-like manner from a small area of origin at the cricoid cartilage to a more extended area of attachment at the inferior thyroid cornu. The ligament consists of one (7.5%) to four (12.5%), in most cases of three (45.0%) or two (35.0%), individual parts oriented from mediocranial to latero-caudal. The inferior laryngeal nerve courses immediately dorsal to the ligament. In 60% it is covered by fibers of the posterior cricoarytenoid muscle, in the remaining 40% it is not. In this latter topographic situation there is almost no soft tissue interposed between the nerve and the hypopharynx. Therefore, the nerve may be exposed to pressure forces exerted from dorsally. It may be pushed against the unyielding posterior cricothyroid ligament and suffer functional or structural impairment. Probably, this mechanism may explain some of the laryngeal nerve lesions described in the literature after insertion of gastric tubes.

Arborization of the inferior laryngeal nerve and internal nerve on the posterior surface of the larynx

The morphological patterns of the inferior laryngeal nerve and internal laryngeal nerve display complex arborizations. This paper attempts to identify and clarify these patterns. Dissections were performed on 105 adult Japanese cadavers, and observations were made on 201 sides. Results showed that the communications between the inferior laryngeal nerve (ILN) and internal laryngeal nerve (ITLN) could be classified into two types and three subtypes. Also, the ITLN displayed three characteristic patterns at the arytenoid cartilage. These communications produce complex arborizations of the ILN as it enters the larynx. This may explain the variety of potential clinical symptoms observed after thyroid surgery or neck dissections.

A review of laryngeal paralysis in dogs

Laryngeal paralysis is now a frequently recognized disorder, particularly in older dogs of certain breeds such as the Labrador retriever, Afghan Hound and Irish Setter. The presenting signs may consist of exercise intolerance, inspiratory stridor, inspiratory dyspnoea, gagging, coughing and dysphonia. Two forms of laryngeal paralysis exist, hereditary and acquired. The hereditary form is found in young dogs and transmitted by an autosomal dominant gene. At present little is known about the aetiology of acquired laryngeal paralysis and therefore treatment is directed at relieving the laryngeal obstruction. Recent reports indicate that arytenoid lateralization achieves the best results as a method of surgical correction.

Anatomy of the hyoid apparatus in Odontoceti (toothed whales): specializations of their skeleton and musculature compared with those of terrestrial mammals

BACKGROUND

The hyoid apparatus of odontocetes (toothed whales) serves as a major attachment point for many of the muscles and ligaments subserving breathing, swallowing, and sound production.

METHODS

This study examines the hyoid apparatus in 48 specimens of ten odontocete genera (Phocoena, Lagenorhynchus, Stenella, Delphinus, Tursiops, Grampus, Globicephala, Mesoplodon, Physeter, and Kogia) collected post mortem from beach strandings.

RESULTS

The odontocete hyoid apparatus, as that of their closest terrestrial relatives, the artiodactyls, is divisible into a basal portion (basihyal, paired thyrohyals) and a suspensory portion (paired ceratohyals, epihyals, stylohyals, and tympanohyals) connecting the basal portion to the skull base. Unlike other terrestrial mammals, the basal portion lies inferior to the laryngeal aditus, is flattened dorso-ventrally, and is relatively large, thus providing a broad surface area for muscle attachments. The suspensory elements are not as flattened and are joined by synovial joints (except for epihyal-stylohyal fusion). Muscular specializations include enlargement of those which retract the hyoid apparatus (e.g., sternohyoid) or control the tongue (e.g., styloglossus, hyoglossus). These muscles may be particularly important in a specialized prey capture behavior called suction feeding. In addition, the hyoid apparatus has a tilted placement, which allows asymmetrical enlargement of the piriform sinuses. Asymmetry is also seen in the muscular attachments between the larynx and the hyoid apparatus. The most pronounced differences from the basic pattern are observed in two families: Physeteridae and Ziphiidae.

CONCLUSIONS

The derived position and shape of the odontocete hyoid apparatus may have evolved to subserve several specialized upper respiratory/digestive tract functions, such as simultaneous feeding (suction and swallowing) and sound production.

Interarytenoid notch height relative to the vocal folds. Pilot study

We measured interarytenoid notch height (IANH) in 20 young children who required direct laryngoscopy under general anesthesia. By means of a specifically designed instrument, we found that the average IANH approximated 3 mm. Laryngeal incompetence on swallowing or in the presence of gastroesophageal reflux is associated with a low IANH (p < .0001). Therefore, IANH may be a measure of relative laryngeal incompetence.

Design and development of ultrathin-walled, nonkinking endotracheal tubes of a new "no-pressure" laryngeal seal design. A preliminary report

BACKGROUND

Endotracheal tubes (ETTs) of conventional design and manufacture greatly increase the air-flow resistance of the upper airways. This increase in upper-airway resistance can lead to a significant increase in the work of breathing and may necessitate the use of assisted mechanical ventilation. Current ETTs are relatively stiff and contribute greatly to patient discomfort. The inflatable cuffs now mounted onto the ETTs function well in short-term use but impart significant morbidity when used over longer periods. These issues were addressed by the designing of a low-resistance ETT.

METHODS

Using new techniques, we developed ultrathin-walled, wire reinforced ETTs of conventional configuration and ETTs the oropharyngeal-section diameter of which was a few millimeters larger than the diameter of the tracheal section. The wall thickness was a constant 0.20 mm. The wire reinforcement was stainless steel flat wire or superelastic nickel-titanium alloy. The superelastic nickel-titanium alloy reinforcement made those ETTs crush-proof; after forceful manual compression, recovery was complete. To obtain a seal with the upper airways, we first shaped a short section of the oropharyngeal section of the ETT from round to oval (or egg-shaped) to conform better to the larynx. We then attached to this segment numerous soft, pliable, 0.025-0.075-mm-thick rings of polyurethane to occlude voids for potential air leaks from within the larynx.

RESULTS

In vitro pressure-flow studies showed a decrease by as much as four- or fivefold in air-flow resistance in the adult ETT range, effectively increasing the internal diameter by 2.3-3.7 mm, compared with conventional ETTs of the same outside diameter. In vivo studies for 24 h in sheep showed no air leaks at airway pressures to 30 cmH2O and minimal leak at greater pressures. The gross appearance of the trachea was normal.

CONCLUSIONS

Although the new tubes appear to offer advantages to those currently used, testing in humans is required to assess the clinical utility of the tube-cuff design.

Adult intubation for beginners

The UKCC's 'Scope of Professional Practice' validly points out that, 'Practice takes place in a context of continuing change and development' partly 'as a result of new approaches to professional practice'. Consequently, demands are made on educational institutions to prepare professionals for new practice. One of the new skills, which is now being taught to nurses on the Anaesthetic Nursing Course at the Eastern Area College, is that of endotracheal intubation. Bearing in mind the all-important proviso that 'As a registered nurse, midwife or health visitor, you are personally accountable for your practice', it is essential that post registration education 'equips practitioners with additional and more specialist skills necessary to meet the special needs of patients and clients'. This article is therefore designed as an introduction to the basic rationale, anatomy and procedural skills necessary for safe intubation.

Objective assessment of posterior choanae and subglottis

The assessment of children with suspected stenosis of the posterior choanae and the subglottis can be arbitrary and subjective. A study was therefore undertaken to assess the normal size of both posterior choanae and subglottis in normal children and ascertain their relationship. The size of the posterior choanae in 72 children ranged from 3-9.3 mm (3-5.5 mm when less than one year old, and 6.1-9.3 mm when older than one year). The two sides were of equal size in 51 children (p < 0.001), in 16 children the right side was larger than the left (p < 0.01), and in 5 children the left was larger than the right side. The subglottic size in 52 children ranged between 4.2-9.3 mm (1.2-5.5 mm when less than one year old, and 6.1-9.3 mm, when older than one year). The size of the subglottis was of equal size or within 1.0 mm of the average size of the two posterior choanae in 41 children (p < 0.001), and of different sizes in 11 children. Accurate and objective assessment of either area can therefore be made by measuring and comparing the two sizes in the same child.

Effects of chemical restraint on the endoscopic appearance of laryngeal and pharyngeal anatomy and sensation in adult cattle

Effects of 2 drugs commonly used for chemical restraint of cattle were evaluated for their effect on laryngeal and pharyngeal anatomy, function, and response to stimuli. Eighteen adult Jersey cows, free of respiratory tract disease, were studied. Cows were assigned at random to 1 of 3 treatment groups. Endoscopic evaluations were performed before and at a predetermined time interval after administration of each drug. Responses to stimuli were evaluated by stimulating 7 preselected sites (epiglottis, left and right arytenoid cartilages, left and right vocal folds, and left and right dorsolateral pharyngeal walls) with a closed, transendoscopic biopsy probe. Xylazine HCl (0.05 mg/kg of body weight, i.v.) was administered to group-1 cows (n = 6), and endoscopy was repeated 5 minutes after administration of the drug. Xylazine (0.07 mg/kg, i.v.) was administered to group-2 cows (n = 6), and endoscopy was repeated 5 minutes after administration of the drug. Acepromazine maleate (0.035 mg/kg, i.v.) was administered to group-3 cows (n = 6), and endoscopy was repeated 10 minutes after administration of the drug. Responses to stimuli were scored as brisk (0), moderate (1), slow (2), and absent (3). Scores for responses to stimuli were compared, using the Wilcoxon signed-rank test for data within groups, and a general linear models procedure, using the Kruskal-Wallis test between groups. Interobserver agreement rates were generated for each group. A value of P < 0.05 was considered significant. Xylazine profoundly changed laryngeal sensitivity and function at both dosages. The corniculate processes of the arytenoid cartilages were observed to be in a markedly adducted position after sedation.(ABSTRACT TRUNCATED AT 250 WORDS)

Speaker race identification from acoustic cues in the vocal signal

One-second acoustic samples were extracted from the mid-portion of sustained /a/ vowels produced by 50 black and 50 white adult males. Each vowel sample from a black subject was randomly paired with a sample from a white subject. From the tape-recorded samples alone, both expert and naive listeners could determine the race of the speaker with 60% accuracy. The accuracy of race identification was independent of the listener's own race, sex, or listening experience. An acoustic analysis of the samples revealed that, although within ranges reported by previous studies of normal voices, the black speakers had greater frequency perturbation, significantly greater amplitude perturbation, and a significantly lower harmonics-to-noise ratio than did the white speakers. The listeners were most successful in distinguishing voice pairs when the differences in vocal perturbation and additive noise were greatest and were least successful when such differences were minimal or absent. Because there were no significant differences in the mean fundamental frequency or formant structure of the voice samples, it is likely that the listeners relied on differences in spectral noise to discriminate the black and white speakers.

Endoscopic evaluation of the nasopharynx, pharynx, and larynx of Jersey cows

Endoscopy of the nasopharynx, pharynx, and larynx was performed in each of 25 adult Jersey cows, age and body weight of which ranged from 2 to 6 years and 300 to 365 kg, respectively. The endoscopic appearance of normal anatomic structures of the proximal portion of the airway were described. Observations specific to female dairy cattle were: the nasal septum, which tapered caudodorsally in the distal third of the nasal passage; the ability to observe both ethmoturbinates from the same viewing side; presence of a pharyngeal septum; the nasopharyngeal opening of the auditory tubes dorsolateral to the pharyngeal septum; and the appearance of the larynx--a triangular epiglottis with round borders and prominent corniculate process of the arytenoid cartilages. Tracheoscopy was performed in 13 cows. Of 11 cows for which the soft palate could be observed immediately after withdrawing the endoscope, 7 had dorsal displacement of the soft palate.

Analysis of mathematical model for osseous factors in difficult intubation

A two-dimensional model of the factors relevant to difficult laryngoscopy was analysed mathematically to determine clinical implications and limitations. The model describes the space into which the "inevitable residual volume" of the tongue (that part remaining anterior to the blade at laryngoscopy) can be displaced to permit a view of the larynx. Four points are used: the tip of the upper incisors; a point on the anterior airway just above the larynx; the mid-point between the mandibular condyles and the internal mid-point of the symphysis. The number, F, was defined by a formula developed from their spacial relationships. Decreasing F values imply an increasing likelihood of difficult laryngoscopy. The analysis investigated the effects of: translation of individual points; plotting individual point positions for specified F-values; translating adjacent pairs of points; treating any three points as a triangle which rotates about each of its apices; and lastly, translating three points independently. During manipulations the model behaved well mathematically. Single point analysis implied that jaw recession and a non-protruding mandible were comparable in effect. Closing the mouth around the laryngoscope blade maximised F-values. Prominence of the maxilla required greater forward displacement than backward movement of the symphysis for equivalent F-value change. One particular triangular rotation suggested an entirely novel mechanism for difficulty (the "hi-slung mandible") where the condyles are positioned more rostral than normal. An otherwise normal jaw with this configuration recedes markedly on opening. Further studies are required to validate the model. Accurate quantification of individual factors in difficult laryngoscopy may then be feasible.

What is the best way to determine oropharyngeal classification and mandibular space length to predict difficult laryngoscopy?

BACKGROUND

Previous studies have suggested that the degree of visibility of oropharyngeal structures (OP class) and mandibular space (MS) length can predict difficult laryngoscopy. However, those studies were either inconsistent or omit description of how to perform these tests with regard to body, head and tongue position, and the use of phonation, hyoid versus thyroid cartilage and inside versus outside of the mentum. The purpose of this investigation was to determine which method of testing best predicts difficult laryngoscopy.

METHODS

In each of 213 consenting adults the OP class was determined in 24 method combinations: two body positions (sitting and supine), three head positions (neutral, sniff, and full extension), two tongue positions (in and out), and with and without phonation. In each patient MS length was measured in 24 method combinations: two body positions (sitting and supine), three head positions (neutral, sniff, and full extension), two distal end points (hyoid and thyroid cartilage), and two proximal end points (inside and outside of the mentum). In each patient the laryngoscopic grade was determined at the time of induction of anesthesia. We defined laryngoscopic grades III (n = 24) and 4 (n = 0) as difficult. The area under the receiver operating characteristic curve (ROC area) for each combination was used to compare the combinations and determine significant differences: ROC area = 0.5 implied a totally uninformative combination and ROC area = 1.0 a combination that predicted perfectly. Logistic regression analysis was used to calculate a predictor of difficult intubation that combined both OP class and MS length (the performance index). The performance index could then be used to calculate sensitivity, specificity, positive and negative predictive value, and probability of difficult intubation.

RESULTS

The ROC areas for the different combinations used to assess OP class ranged from 0.78 to 0.94. The best combination was with the patient sitting, head in extension, tongue out, and with or without phonation. For MS length, the ROC areas ranged from 0.58 to 0.77; the best combination was the patient sitting, with the head in extension, with distance measured from the inside of the mentum to the thyroid cartilage. Combining the OP class and MS length (performance index = 2.5 X OP class - MS length in centimeters) significantly increased predictability of difficult intubation. At performance index = 0 and = 2, the probability of difficult intubation was 3.5% and 24%, respectively. With clinically relevant cutpoints for the performance index it was found that most difficult intubations could be predicted, but approximately half of those predicted to be difficult would in fact be easy.

CONCLUSIONS

Based on the above ROC areas and ease of performing the test for the patient, we recommend that these tests be performed with patients in the sitting position, with the head in full extension, the tongue out, and with phonation, and with distance measured from the thyroid cartilage to inside of the mentum. Nevertheless, it is clear that these two tests, either used alone or in combination, will fail to predict a few difficult laryngoscopies and that they will predict difficult laryngoscopy in a significant number of patients in whom the trachea is easy to intubate.

[Anatomy of the pharyngo-laryngeal crossing]

The anatomy of the pharyngo-laryngeal region can be considered from different points of view. The anesthetist should be aware of some important details that will help him during the intubation maneuvers. The anatomist and the ENT surgeon will guide him through the following landmarks: the basis of the tongue, the epiglottis, the arytenoids and the vocal cords.

Anatomic considerations in botulinum toxin type A therapy for spasmodic dysphonia

Chemodenervation by injection of botulinum toxin type A into the vocal fold(s) has become the preferred treatment for patients with adductor spasmodic dysphonia. Injection may be done either perorally or transcutaneously; each method has its advocates and advantages. The authors have used the transcutaneous transcricothyroid membrane route exclusively with satisfactory results in more than 50 patients. Temporary breathliness and aspiration are common. The preferred injection site should be as close as possible to the motor end plates of the affected muscle. The thyroarytenoid muscle end plates are distributed throughout the muscle, whereas in the lateral cricoarytenoid muscle they are located in band in the center of the muscle. The transcutaneous injection site is below and posterior to the midpoint of the vibrating vocal fold as visualized by indirect laryngoscopy. The proximity of this site to the lateral cricoarytenoid muscle suggests that postinjection breathiness and aspiration may be related to spread of botulinum toxin type A to the lateral cricoarytenoid muscle. However, it is likely that thyroarytenoid muscle paresis is mainly responsible for this side effect and that the rapid clearing of the breathy dysphonia in the face of prolonged relief of spasmodic dysphonia symptoms suggests the action of an adaptive neural response, such as axonal sprouting. Further research of this subject is warranted.