Upper airway anatomy and function

Upper airway anatomy and functionBailey reading Introduction

The upper airway includes the nasal and oral cavities, the pharynx, and the larynx; the function design is far from ideal because ingested food and water must traverse the upper airway to reach the alimentary tract.

The pharynx must serve two conflicting functions : - rapidly constrict during swallowing, - maintain patency during the negative pressure generated by inspiration.

Breathing and speech must be interrupted during a swallow.Pharyngeal AnatomyThe pharynx is an irregularly tubular structure, extending from the base of the skull to the esophageal inlet (Fig. 49.1). The pharynx has anterior openings into the nasal and oral cavities, and inferiorly it opens into the larynx and esophagus. There are three segments: the nasopharynx, the oropharynx, and the hypopharynx.The nasopharynx can be sealed off from the oropharynx by simultaneous elevation of the soft palate and formation of a fold in the pharyngeal walls, known as Passavant ridge.

The pharynx must serve two conflicting functions : - rapidly constrict during swallowing, - maintain patency during the negative pressure generated by inspiration.

The posterior and lateral walls of the pharynx are composed of three pharyngeal constrictor muscles attached to the cervical vertebrae posteriorly: superior constrictorMiddle constrictorInferior constrictor

The superior constrictor is suspended from the base of the skull, the medial pterygoid plate, the pterygomandibular raphe, the mylohyoid line of the mandible, and the lateral tongue.The middle constrictor attach anteriorly on the hyoid bone and the stylohyoid ligament.The inferior constrictor attaches to the thyroid and cricoid cartilages.

Activation of these muscles constricts the pharynx; there is no evidence to support the concept that they contribute to stability of the airway.Pharyngeal patency during the negative pressure generated with inspiration is maintained by muscles that dilate the lumen by pulling the base of the tongue or hyoid bone anteriorly. These muscles include: the genioglossus, the geniohyoid, and the anterior belly of the digastric muscle.Pharyngeal Airway PhysiologyMaintenance of upper airway patency is a peculiarly human problem. Some degree of airway collapse occurs during sleep in all humans, and obstructive sleep apnea (OSA) is extremely common. Sleep-disordered breathing is extremely rare in any other animal .

The instability of the human pharyngeal airway seems to be a result of the inferior displacement of the larynx during development (2). As a result, the pliable pharyngeal walls are suspended from the base of the skull and mandible with little skeletal support.Otot-otot yg menjaga patensi, yaitu otot genioglossus, geniohyoid, dan digastric anterior sesungguhnya adalah otot-otot dilatasi faring yang distimulasi oleh tekanan negatif airwayPada pasien OSA dinding faring lebih mudah kolaps.Karena dinding faring mudah kolaps (lentur), maka pharynx berperan seperi/sebagai Starling resistor mekanisme resistor yang dipengaruhi oleh :Difference between the upstream and downstream (i.e., intrapleural) pressuresDifference between the upstream pressure and the collapsing forces (paling penting pengaruhnya).

Jadi bisa dikatakan bahwa jika tekanan udara inspirasi dari hidung tidak cukup kuat untuk mencegah faring kolaps dan tetap terbuka, maka tidak ada udara yang akan masuk ke paru,meskipun otot-otot pernafasan kontraksi hebat akibatnya timbul apnu obstruktif. Patency of the upper airway during breathing depends on active contraction of muscles that dilate the pharynx and open the larynx.Laryngeal AnatomyEpiglottis --the most superior portion of the larynx , which projects posteriorly into the pharynx. The vallecula is the pouch between the base of the tongue and the epiglottis. Interiorly, the glottis is seen as a roughly triangular opening during inspiration and a narrow slit during phonation.

The true vocal folds comprise the anterior edges of the glottis. Superior and lateral to the true vocal folds are the false vocal folds.

The ventricle is a narrow space between the true and false folds.

The posterior glottis is formed by the two arytenoid cartilages and the intervening mucosa. The arytenoids are the posterior attachments of both the true and false vocal folds.

Opening and closing of the glottis is accomplished by action of muscles that move the arytenoids.

There is a mucosal bridge between the epiglottis and the arytenoid on each side, known as the aryepiglottic fold. These folds serve as levees between the swallowing channels and airway, by separating the piriform fossae from the glottis.

The piriform fossae are mucosal-lined spaces lateral to the aryepiglottic folds but medial to the laryngeal skeleton (Figs. 49.2, 49.3, and 49.4), and are the pathways by which ingested food and liquid are conveyed to the esophagus.

Skeleton

The laryngeal skeleton is made up of several cartilages and one bone strung together in series and suspended from the skull base and mandible (Fig. 49.5). Laryngeal motion can be caused by both intrinsic muscles, which arise and insert on laryngeal cartilages, and extrinsic muscles, which connect the larynx to other structures. Descent of the trachea during inspiration produces widening of the glottis. This phenomenon is a result of the ligamentous interconnections of the laryngeal skeleton.

19The hyoidsupports the larynx and stabilizes the hypopharynx, is roughly U-shaped, with the two free ends projecting posteriorly as the greater cornua and the lesser cornua are two small bumps on the superior anterior surface. hyoid is connected to the thyroid cartilage by the broad thyrohyoid membrane. A bursa in this membrane enhances vertical mobility of the larynx. Laterally, the edges of the membrane thicken to form the thyrohyoid ligaments.

The thyroid cartilageis composed of two halves fusedanteriorly at a sharp angle (90 degrees in males and 120 degrees in females). The posterior border has superior and inferior cornua: the superior cornu attaches to the thyrohyoid ligament, whereas the inferior articulates with the cricoid cartilage. The thyroid cartilage begins to gradually ossify after the age of 20 years. This process accounts for many age-related changes in pitch and resonance of the voice.The epiglottis is a fibroelastic cartilage, attached anteriorly in the midline to the inner surface of the thyroid cartilage and supported by the hyoepiglottic ligament. The free end of the epiglottis projects into the hypopharynx.

The cricoid cartilageis the skeletal support of the subglottis. - The subglottis is the only point in the airway with a completely rigid diameter and has a smaller cross-sectional area than the tracheaAnteriorly, the cricoid is about 1 cm high, with a smooth curved surface. Posteriorly, it is 2 to 3 cm high, and the superior surface is flattened centrally to provide an area of articulation for the arytenoid cartilages. Posterolaterally, on each side, the cricoid articulates with the inferior cornu of the thyroid cartilage to form a visorlike apparatus, allowing rotation in a sagittal plane, which opens or closes the anterior cricothyroid space.

arytenoid cartilage is a somewhat pear-shaped mass. The broad base articulates with the cricoid in a complex synovial joint, allowing multiaxial rotation but minimal translation (6). The vocal process, an anterior and medial projection of the arytenoid, is the posterior segment off the vocal fold (Fig. 49.6). Two other small sesamoid cartilages, the corniculate and the cuneiform, are located superior to the arytenoid and support the aryepiglottic fold.

Two fibroelastic membranes are important components of the larynx.

The conus elasticus provides support to the vocal fold. From its lateral attachment to the cricoid, it extends anteriorly to the midline lower edge of the thyroid cartilage and posteriorly to the vocal process of the arytenoid. Its free edge forms the vocal ligament. The qua-drangular membrane supports the supraglottis. It connects the epiglottis with the arytenoid and the corniculate cartilages. The superior free edge is draped in mucosa to form the aryepiglottic fold, whereas the inferior edge is a part of the false vocal fold (Fig. 49.7).

Muscles

Motion of the vocal folds is affected primarily by the intrinsic laryngeal muscles: posterior cricoarytenoid muscle, the only abductor of the glottis, origo:the posterior surface of the cricoid, insertio: arytenoid. Contraction of this muscle externally rotates the arytenoid, displacing the vocal process superiorly and laterally, resulting in abduction of the glottis (6). The lateral cricoarytenoid is an adductor with origin on the lateral cricoid and insertion on the arytenoid. This muscle pulls the muscular process forward, rotating the vocal process medially. The thyroarytenoid originates on thyroid cartilage to insert on the vocal process of the arytenoid. It exerts anterior traction on the vocal process, increasing vocal fold tension, thickness, and stiffness. In the absence of cricothyroid muscle contraction, it also reduces tension in the mucosal cover. The thyroarytenoid muscle is often considered to be divided into two separate muscles: the medial thyroarytenoid (vocalis) and the lateral thyroarytenoid. The cricothyroid muscle pulls the cricoid and thyroid cartilages together anteriorly to increase the length and tension of the vocal folds.

The interarytenoid muscle, the only unpaired laryngeal muscle, adducts the vocal folds (Fig. 49.6). The smallest laryngeal muscle, a very small band of muscle fibers between the epiglottis and arytenoid, constricts the supraglottic inlet.Extrinsic laryngeal muscles include the mylohyoid, digastric, and stylohyoid muscles, which suspend the larynx superiorly, and the cervical strap muscles: the omohyoid, sternohyoid, sternothyroid, and thyrohyoid.

Extrinsic muscles elevate or depress the larynx or move it anteriorly or posteriorly. Extrinsic muscle activity can indirectly adduct, abduct, or tense the vocal folds or constrict the supraglottis.

Nerve SupplyThe vagus nerve supplies the larynx through two branches, the superior laryngeal nerve and the recurrent laryngeal nerve. The superior laryngeal nerve exits the vagus below the nodose ganglion and branches into two divisions. The internal branch is purely sensory, carries afferent fibers from supraglottis and vocal folds, and enters the larynx laterally through the thyrohyoid membrane. The external branch supplies motor fibers to the cricothyroid muscle.Mucosal CoverThe mucosal cover of most of the upper airway is respiratory epithelium, with numerous mucous glands (Fig. 49.8). Over the free edge of the vocal fold, mucosa is adapted for periodic vibration with squamous epithelium and no mucous glands. A highly specialized lamina propria separates the epithelium from underlying muscle (10). The lamina propria serves as a shock absorber, or impedance matcher, so that the epithelium can vibrate freely, without restriction by the bulky underlying muscle.

The lamina propria of the vocal fold contains three layers: superficial, intermediate, and deep. Each layer has unique mechanical properties because of varying densities of elastic and collagenous fibers. The deep layer, or vocal ligament, is the stiffest, due to a high concentration of collagen fibers. Elastic fibers are most numerous in the intermediate layer and gradually decrease toward the epithelium and muscle. The superficial layer of the lamina propria is often referred to as Reinke space, although it is not actually a potential space. This layer has the lowest concentration of both elastic and collagenous fibers and offers the least impedance to vibration.

Vocal fold mucosaRespiratory Physiology Of the LarynxThe most primitive function of the larynx is that of a sphincter, preventing the ingress of anything other than air into the lungs. Other functions include coughing, Valsalva maneuver, and the regulation of airflow in and out of the lungs. The larynx also serves as a sensory organ and contains receptors that influence the control of breathing and even affect cardiovascular function.

CoughCough ejects mucus and foreign matter from the lungs and helps to maintain patency of the pulmonary alveoliA cough has three phases: inspiratory, compressive, and expulsive. First, the larynx opens very widely to permit rapid and deep inspiration. If the cough is voluntary, the degree of glottal abduction and inspiratory effort is proportional to the intended strength of the cough. The compressive phase is produced by tight closure of the glottis and strong activation of expiratory muscles. During the expulsive phase, the larynx suddenly opens widely, with a sudden outflow of air in the range of 6 to 10 L per second.

Valsalva ManeuverForced expiration against a tightly closed glottis is known as the Valsalva maneuver. The true vocal folds offer more resistance to inspiratory than expiratory airflow. However, very tight closure of both true and false vocal folds enables the larynx to resist very strong expiratory forces. It is important in defecation because the pressure is transmitted to the abdominal cavity. Valsalva also serves to stabilize the thorax during heavy lifting by the arms.

Regulation of AirflowThe larynx is ideally located to regulate the flow of air in and out of the lungsObservations of laryngeal movement demonstrate that the glottis widens during inspiration and narrows during expiration, Opening, or abduction of the larynx, facilitates breathing by decreasing resistance to airflow. Two forces contribute to inspiratory opening of the larynx: longitudinal tension on the laryngeal skeleton, caused by the descent of the trachea, and contraction of the posterior cricoarytenoid muscle. Active laryngeal abduction is a primary action of breathing, because the posterior cricoarytenoid muscle consistently begins to contract before the diaphragm. The larynx opens more widely during inspiration with increasing effort of breathing and in response to negative upper airway pressure.

39Expiratory adduction of the larynx is sometimes a passive phenomenon, but laryngeal abductor activity can decrease the rate of breathing by prolonging expiratory duration. With very strong respiratory demand, the posterior cricoarytenoid muscle continues contracting during expiration, after the diaphragm has relaxed. This results in decreased resistance and faster outflow of air, which shortens the duration of expiration and increases the rate of breathing. During most conditions of breathing, respiratory rate is primarily controlled by varying the rate of exhalation.

In addition to dynamic control of airflow, the static larynx exerts mechanical influences on airflow. At any given glottic aperture, resistance to airflow in the inspiratory direction is much greater than resistance to expiratory flow. Because of this, conditions that cause laryngeal obstruction, such as edema, papillomas, or laryngeal paralysis, usually produce inspiratory stridor before expiration is impaired.Sensory Input to Respiratory ControlThe larynx is not only an effector organ; it is also richly supplied with a variety of sensory receptors that exert influences on breathing and cardiovascular functionThree major types of laryngeal receptors are activated by the process of breathing and have an influence on the central control of breathing: negative pressure receptors; airflow (cold) receptors; and drive receptors, which are probably proprioceptors that respond to respiratory motion of the larynx. Laryngeal receptors also respond to touch and chemical stimuli.Circulatory ReflexesStimulation of the larynx can produce changes in heart rate and blood pressure as seen during general anesthesia and OSA. When upper airway patency is not maintained during sleep, the resulting increase in negative airway pressure can stimulate receptors in the larynx so strongly that cardiac arrhythmias occur. The direct result of laryngeal stimulation on blood pressure is hypertension. However, if laryngeal stimulation produces significant bradycardia or ectopy, the indirect result can be hypotension.

Speech

The human voice results from the coordinated interaction of the larynx, lungs, diaphragm, abdominal muscles, throat, neck muscles, lips, tongue, buccinators, and soft palate. Speech consists of three component processes: phonation, resonance, and articulation. Phonation is the generation of sound by vibration of the vocal folds. Resonance is the induction of vibration of the rest of the vocal tract to modulate and amplify laryngeal output. Articulation is the shaping of the voice into the words that characterize human speech.

Phonation

Sound is produced by the larynx when expiratory airflow induces vibration of free edges of the vocal folds as a result of the interaction of aerodynamic and myoelastic forces. Five conditions must be met to support normal phonation: appropriate vocal fold approximation, adequate expiratory force, sufficient vibratory capacity of the vocal folds, favorable vocal fold contour, and volitional control of vocal fold length and tension. Just before phonation, the vocal folds are approximated in the midline. Exhalation then causes subglottic pressure to rise until the vocal folds are pushed apart. This separation produces a rapid decrease in subglottic pressure. The vocal folds then return to the midline as a result of sudden decrease in pressure, elastic forces in the vocal fold, and the Bernoulli effect. Pressure in the trachea builds once more, and the cycle is repeated. During modal phonation, the vocal fold essentially vibrates as two masses, with the upper edge lagging behind the lower edge. This results in a traveling wave, from caudal to rostral, known as the mucosal wave.

ResonancePhonatory output is modulated by resonance, the induction of vibration in the chest, pharynx, and head with selective amplification of certain component frequencies. Resonance not only gives the voice its characteristic acoustic pattern but can also amplify the voice. Vocal training, for singing and acting or public speaking, concentrates heavily on refining and maximizing resonance, so that the loudest and most pleasing sound can be produced with the least amount of strain or pressure on the larynx. Resonance is controlled by altering the shape and volume of the pharynx, by raising or lowering the larynx, by moving tongue or jaw position, or by varying the amount of sound transmission through the nasopharynx and nose.

Soal-soalSoal-soal (B-II)The muscle which is most important in maintaining patency of the pharyngeal airway is the...Cricothyroid muscleGenioglossus musclePalatoglossus musclePosterior digastric muscle Superior pharyngeal constrictor

Answer : B

Pharyngeal patency during the negative pressure generated with inspiration is maintained by muscles that dilate the lumen by pulling the base of the tongue or hyoid bone anterior include: the genioglossus, the geniohyoid, and the anterior belly of the digastric muscle.

2. The intrinsic laryngeal muscle that opens the glottis is the....Thyrohyoid musleCricothyroid muscleInterarytenoid muscleLateral cricoarytenoid musclePosterior cricoarytenoid muscleAnswer : E3. Laryngospasm, in response to mechanical stimulation of the larynx, is most likely to occur under which of the following condition?HypoxiaDeep sleepHypercarbiaLight anesthesiaStrenuous exerciseAnswer : D

4. Mechanical stimulation of the larynx results in...BronchodilationTachycardiaHypertensionValsava maneuverdisphoresisAnswer: C5. Which of the following is requirement for normal phonation?Normal lamina propiaNormal vital capacityDivergent glottal tractTight glottal closureSense vocal ligamentAnswer: ASoal B-1The vocal folds are abducted by the....Cricothyroid muscleThyroarytenoid muscleInterarytenoid muscleLateral cricoarytenoid musclee. Posterior cricoarytenoid muscle

Answer: E2. Anterior displacement of the muscular process of the arytenoid has the following effect on the vocal foldAdductionAbductionShorteningDecrease in tensionInferior displacementAnswer: A3. A muscle that does not contribute to maintaining patency of the upper airway patency is the..DigastricGeniohyoidGenioglossusPosterior cricoarytenoidSuperior pharyngeal constrictorAnswer: E4. The mucosa of the vibratory edge of the vocal fold is unique because of its specialized....Columnar epitheliumBasement membraneLamina propriaMucus glandCilia

Answer: CThe superior laryngeal nerve supplies motor fibers to the......Superior pharyngeal contrictor muscleLateral cricoarytenoid muscleThyroarytenoid muscleCricothyroid muscleThyrohyoid muscleAnswer: DLaryngeal adductor muscle play a role in the control of breathing by....Decreasing the duration of inspirationIncreasing the duration of expirationDecreasing functional residual capacityLengthening the pause between breathsIncreasing the rate of respirationAnswer : B 7. A direct cardiovascular effect of mechanical stimulation of the larynx is..HypertensionTachycardiaVentricular ectopyPeripheral vasodilatationIncreased cardiac outputAnswer: A8. Excess subglottic pressure would be required for phonation in the presence of..Vocal nodulesVocal fold paralysisiAbductor muscle spasmAdductor muscle spasmVocalis muscle atrophyAnswer: D9. Elevation of vocal pitch with increasing age is due to....Vocal fold edemaDescent of the hyoid boneAtrophy of thecricothyroid muscleThinning of the vocal fold mucosaCalcification of thyroid cartilageAnswer: E10. The structure around which the left recurrent laryngeal nerve courses before ascending back to the larynx is the........Aortic archPulmonary arteryInnominate arterySubclavian arteryLigamentum arteriosumAnswer: E11. The medial border of the pyriform fossa is partially formed by the.....ValleculaHyoid boneConus elasticusThyroid cartilageAryepiglottic foldAnswer: E12. The feature of upper airway that is unique to human isPassavants ridgeThe laryngeal ventricleDescent of the larynx during developmentComplete glottal closure with phonationContact of the uvula with the epiglottic

Answer: C 13. Laryngeal edema is most likely to result inHyperpneaReflex apneaInspiratory stridorExpiratory wheezingProlonged exhalationAnswer: CThank you.........