Physiology Of The Upper Air-Passages

By WALTER J. FREEMAN, M. D.,
OF PHILADELPHIA.

THE study of the physiology of the nose, throat, and larynx is of the greatest practical importance, for it is only by an intimate knowledge of their functions in health that we are able correctly to appreciate the significance of pathological conditions. At times, indeed, when insurmountable difficulties prevent thorough physical examination, we must fall back upon our knowledge of the normal functions of the parts, such as breathing, swallowing, phonation, etc., to obtain a correct diagnosis.

NOSE.

The old idea of the nose as simply an organ of olfaction has given place to an appreciation of the influence it exerts upon the whole economy, not only by its vital functions of warming, moistening, and filtering, the inspired air, but also by its acting as a protective organ to prevent the admission o harmful substances in inhalation.

Functions of the Nose. Respiration. (I) Passage way for air in breathing; (2) warming, moistening, and filtering the inspired air.
Olfaction. (1) Perception flavors in expiration; (2) perception of odors in inspiration.
Phonation. (I) Resonance; (2) production of overtones.
Protection. (1) By sensation (2) by olfaction.
Ventilation. (I) Of the ears (2) of the accessory sinuses.

Respiration. (I) We notice from the dryness Of the throat in mouthbreathing that this is not the passage way intended by nature for the air in inspiration, and we realize that normal respiration should take place through the nose, and that mouth breathing is a pathological condition giving rise to many injurious results.

Paulsen has proved that the air in respiration takes a very different course from that formerly supposed to be the case.

Instead of flowing back along the inferior meatus, the air passes directly upward from the nostril to the superior meatus, whence it falls by a gentle curve toward the chooses.' This shows the old arbitrary division Of the Dose into a lower respiratory and an upper olfactory portion to be, physiologically at least, incorrect. It seems curious that the inferior meatus should thus be avoided by the inspiratory currents, for the inferior turbinals contain the largest amount of vascular tissue. It must be remembered, however, that nowhere in the nose is the air at rest, and as the air in the inferior meatus is more sluggish, it has received more heat, and when drawn into the current raises its temperature more quickly.' The main currents of air pass into the naso pharynx at the highest portion of the choanal arches, and an enlargement of the pharyngeal tonsil, encroaching even slightly upon these openings, impedes respiration much more than does swelling of the ends of the inferior turbinals, blocking to a marked degree the lower portion of the choana (compare Fig. 560).

The course of the air in expiration is nearly the same as in inspiration, except that it is directed higher up i. e., through the posterior part of the superior meatus, a point that we shall soon see is of importance in detecting flavors.

(2) Within the nose the shelf like arrangement of the turbinated bones gives increased extent of surface to the vascular membrane with which they are covered. The interior of the nose is completely lined with mucous membrane that covering the inferior turbinals, the lower portion of the middle, and the posterior ends of the middle and superior turbinals, containing vast systems of blood vessels, which are the chief source of the beat and moisture supplied to the air in inspiration. These blood sinuses are surrounded by involuntary muscular fibers, and, although they are commonly so called, they are not, correctly speaking, true erectile bodies, which consist of large irregular spaces lined with pavement epithelium. This muscular tissue is under the control of the sympathetic system, which reaches the interior of the nose by way of the spheno palatine ganglion, and derives its influence from the cerebrospinal system. It is known that there are vaso dilators as well as vaso constrictors and their centers probably lie in the floor of the fourth ventricle. The dilatation and contraction of the sinuses caused by these nerves are constantly going on, and are physiological actions of great importance. The object is the regulation of the amount of blood in the turbinals, and hence the proper warming and moistening of the inspired air. The mechanism is, indeed, a delicate one which is able to supply the requisite amount of heat and moisture under all the varying changes of temperature and humidity to which animal life is subjected. Thus we notice that when the temperature is cold, the turbinals swell and the passages become more closed. This indicates that the vascular tissue has become filled, and that a large amount of warm blood is being brought into contact with the impeded current of inspired air, raising its temperature to a higher degree. While the swelling of the turbinals is frequently accompanied by increased secretion, this is not necessarily the case, for we may have the one independent of the other. Were it otherwise, in cold weather we should normally have excessive secretion, a condition, however, which, although frequently met with, is due to abnormal sensitiveness of the nasal mucous membrane to contact with cold air. We know that at 32' F. air, to be saturated, require , but 2.1 gr. of water to the cubic foot. Thus the tissues of the nose would be called upon for very little moisture in cold weather did they not, in raising the temperature of the inspired air, also raise its saturation point, which goes to illustrate the nice balance which must normally exist. According to Aschenbrandt and Kayser, the inspired air receives from 20' to 40' of beat,' and becomes saturated, or nearly so,' in its passage through the nose. This renders it suitable for the interchange of oxygen and carbonic acid gas in the lungs, a simple action of osmosis which takes place most perfectly when with warm fluid on one side of a membrane there is warm, moist air on the other.

To supply the large amount of water necessary to moisten the inspired air, Bosworth has calculated that about a pint should be secreted by the nose, and this is obtained from the sinus tissue of the turbinals, together with the tears and the secretion of the muciparous glands.

The function of the nose in filtering the inspired air is practically perfect, for Tyndall has demonstrated that the expired air is free from germs. This takes place, first by action of the vibrissa, the hairs of the vestibules, which hinder the entrance of large particles, and next by the adherence of smaller particles to the moist surfaces of the intricate passages of the nose and naso pharynx. When in large amount, or when the nose is too roomy, or pathological conditions interfere with this normal filtering process, particles may reach the lower respiratory tract. While the mucus is an important agent in arresting the dust, the cilia are in no less degree active in cleansing the surfaces. The ciliary wave in the Dose is toward the naso pharynx, that in the naso pharynx toward the mouth, while that in the lower respiratory tract is upward, so that foreign particles are carried toward the mouth and thus removed, either by expectoration, or, more physiologically, by swallowing. The activity of the cilie depends very much upon the quality of the mucus with which the membranes are covered; for in certain states, when there is much viscidity, it is known that their action is much hindered. This gives rise to a feeling of stuffiness, so great at times that patients with fossa so open that one is able to see the vault through both sides, complain that the nose is obstructed. We see, therefore, the vital functions exercised by the intranasal mucous membrane; and a correct knowledge of its physiological functions should teach us as far as possible to avoid cauterization or destruc¬tion of this tissue, and to remove instead septal overgrowths or to correct deformities of the septum which interfere with respiration.

Olfaction. (I) As a function for yielding pleasure and for serving as a means of information and protection, olfaction has been held in far too low estimation. In man this sense receives very little attention, partly because of' the protected position which the organ of smell occupies, thus greatly diminishing its liability to injury, and the consequent infrequency of disorders of olfaction, but more especially because of the almost universal lack of development and training. It is probable that in the course of evolution, devolution of this sense has taken place, and that in primitive man it was much more highly developed. Indeed, in certain cases we find the sense so acute that its possibilities seem almost incredible.' The increase in size and number of the turbinals would seem to have an important bearing on the sense of olfaction, as furnishing greater extent of surface for distribution of olfactory nerves. While the presence of a fourth or even a fifth turbinal is probably due to a persistence of the sagittal furrows found in the embryo, the fact that a fourth turbinal is present in certain negro tribes in whom olfaction is very acute seems to point toward the lessening of the function in civilized man as due to lack of development of the organ of olfaction.' Not only has there been an apparent degeneration of the sense, but directly bearing upon this, also a decrease in size of the olfactory lobes and the fields of distribution of the nerves.' Thus while most writers claim that the terminal filaments* are distributed to the middle as well as the superior turbinal and the region of the septum opposite, Schultze's investigations, confirmed by von Bruun's careful measurements, have proved that the olfactory epithelium does not reach the lower edge of the superior turbinal by 7 1/2 mm., and that the whole olfactory surface, divided nearly equally between the turbinal and the septum, has an extent of but 257 sq. mm., although this is increased slightly by scattered islands of olfactory cells. The olfactory organ, then, is placed in the remotest region of the nose; and it is, therefore, only by an appreciation of the direction of the air currents in respiration that we are able to understand how it can be acted upon at all by odoriferous particles.

In order that we may detect odors, certain conditions are essential. The perceptive structures must be normal, nasal respiration must be unhindered, and the surface must be moist.' The external nose and the power of sniffing,' are also necessary in order that the current of air may be properly directed into the superior meatus. Then again, that the odor of substances may be perceived, they must be either in a gaseous state or in a state of fine subdivision and capable of absorption. Whether the odoriferous substances cause olfaction by their specific weight, by their power to absorb beat (Tyndall) by their chemical properties, or by their specific action on the pigment cells of the olfactory region, can probably never be stated definitely. It is a matter of speculation and theorizing at present, and many ideas as to its mode of action have been advanced. It seems probable that the theory that olfaction depends upon the chemical composition (Haycraft) and molecular weight of the substance will finally be generally accepted.

(2) The greater part of the sensation that we designate as taste is, in reality, olfaction 2 that is, olfaction during expiration. The term taste should, strictly speaking, be limited to perception of sweet, sour, bitter, and salt, the only sensations detected by the nerves of gustation; but so narrow an interpretation cannot be adhered to as yet. One can readily be convinced of the truth of this statement by holding the nose while drinking or eating, for thus the currents of air are unable to pass through the nose and all flavors and odors are unperceived. Also in cases of imperforate choana, although the organs of olfaction are normal and the nasal fossa otherwise free, the senses of smell and taste are both in abeyance because of the absence of both inspiratory and expiratory currents through the nose. It is in the experience of everyone that severe coryza will likewise rob a person not, only of smell, but in a great part also of taste. The great delicacy of the sense of taste seems to be due to the course of the air in expiration, as it passes higher in the nose and thus more powerfully affects the olfactory region.

Phonation. (I) Resonance being an increase in the volume of sound, the voice gains its strength and character by the reverberation of the air contained in the nasal passages and accessory sinuses. The hard palate must be looked upon as a sounding board and as a decided factor in transmitting the vibrations to the chambers above. We can, then, understand the reason why growths that obstruct the nasal cavities destroy the character of the voice, not only by preventing the passage of air through the nostrils, but by interfering with vibration. While the accessory sinuses have been variously stated to be intended to lighten the skull, to act as sources of warm air and as reservoirs for mucus to moisten the nose, and for use in olfaction, these functions are of little or no weight in comparison with the important part they play as, resonating chambers. Even the frontal sinuses seem to have influence in this direction; for the native Australian negroes, who have no frontal cavities, have voices singularly lacking in resonance, a peculiarity said to be due to this malformation. The explanation of the musical voice of the African negro, so contrasted with the unsympathetic tones of the American Indian, seems to lie in the greater size of the antra in the former race.

(2) The nose and naso pharynx are also necessary, as Helmholtz has shown, for the production of overtones, which give character and increased richness and volume to the voice.

Protection. (I) We have already spoken of the protection afforded by the nose in removing from the inspired air foreign particles which would otherwise penetrate to the delicate pulmonary alveolar But the nose serves also by its sensitiveness to touch to prevent injurious substances from gaining admittance, or by calling forth reflex action, such as sneezing, to cause their expulsion. For these purposes we have an abundant supply of both sympathetic and sensory nerves distributed to the interior of the nose. The trigeminus is the great sensitive nerve of the Dose, and transmits the impressions received through both its ophthalmic and superior maxillary branches. Thus the entrance of irritating substances first gives rise to a cessation of breathing, followed by a forcible expiration to remove the offending material. This is usually accompanied by a free flow of mucus due to the irritation of the trigeminus and sympathetic the former exciting an abundance of clear, non viscid secretion, and the latter a scanty, but very viscid, flow.

(2) The importance of olfaction in protecting the organism against injurious air and food is seldom appreciated, although its function in enabling certain animals, such as the carnivora, to track their prey and procure food, and others, such as the deer or rabbit, ill protected by nature for selfpreservation, to avoid danger, is universally recognized.

Ventilation. (I) The part plaved by the nose in the function of ventilating the middle ears can best be understood by observing the interference which takes place when nasal respiration is obstructed. We know from the Toynbee experiment that of swallowing while the nostrils are closed that the air within the tympani is rarefied and the membranes become retracted, Grave consequences frequently arise from the persistence of the malposition of the tympanic membranes thus taking. place in cases of hypertrophied turbinals, deformities of the nasal septum, etc., which obstruct the free passage of the air through the nose, and therefore interfere with ventilation through the Eustachian tubes.

(2) A somewhat similar, action takes Place in the accessory sinuses, although the effects cannot be directly observed and do not usually give rise to such serious results. According to the experiment of Braune and Clausen, while the pressure in the nose in breathing is equal to from 7 to 10 mm. of water, in the act of sniffing the vacuum formed in the superior maxillary sinus is equal to a negative pressure of 780 mm. of water. This explains Randall's observation that by sniffing one may readily produce hemorrhage from the lining membrane of these cavities, especially when they are acutely congested.

NASO PHARYNX.

The naso pharynx possesses no special sense, but the location here of the pharyngeal tonsil and numerous muciparous glands, whose functions are those of protecting and lubricating the throat, makes it of great importance. It serves also as a resonating chamber of great value for the voice, and contains muscles by whose action the tympanic cavities are ventilated.

While the pharyngeal tonsil per se is too often considered an abnormal growth, and its function as a germinating center for leukocytes is overlooked, its enlargement interferes so markedly with the vital processes of free nasal breathing and normal ventilation of the ears that its physiological functions should not weigh against such important considerations when damage is threatened by its presence. It has been said that the function of the pharyngeal tonsil as a source of lubricating secretion for the pharynx is of no im¬portance judging from the atrophic processes which affect it in adult life. Granting that this pathological condition is widespread, so that the most familiar picture is that of absence or of great reduction in size, it is nevertheless my experience that only those throats can be looked upon as normal in which all the tonsils, although small, are present and in good condition. So, also, in the nose, the sclerotic condition of the turbinals in late adult life, termed senile atrophy, is looked upon as the natural accompaniment of age because of the frequency of its occurrence, in apparent forgetfulness of normal though rare cases, where the turbinals are as large and smooth as in youth.

Sensation in the naso pharynx is supplied not only by the trigeminus and glosso pharyngeal nerves, but also by the superior laryngeal. From this fact arise many erroneous impressions in patients, who refer to the region of the larynx sensations arising in the naso pharynx.'

The ventilation of the ears is brought about by the action of the palatal muscles. While the velum hangs relaxed, the openings of the Eustachian tubes are nearly vertical slits ; but in the act of swallowing they open and become somewhat triangular in shape, allowing the free entrance of air. During " empty " swallowing this is even more pronounced, for the soft palate then ascends to its utmost limits, and in this manner the regular physiological ventilation is constantly provided for.

MOUTH.

Among the many functions Of the mouth, want of space will permit only a brief reference to certain ones bearing directly upon our subject. Besides those concerned in deglutition, the mouth has a most important influence on articulation, the consonants and many of the vowels being formed by the movement of the lips and tongue. It also acts as a speaking trumpet to throw the concentrated and amplified sounds in definite directions. By means of the special sense supplied by the glosso pharyngeal and lingual nerves we are able to distinguish only the sensations Of salt, sour, bitter, and sweet. These impressions are conveyed to the centers of taste in the brain through the fibers of the chorda tympani from the anterior two thirds of the tongue, and through the glosso pharyngeal nerves from the posterior third.

While the nerves of special sense of the nose and mouth contribute much to our pleasure in eating and stimulate the powers of salivary secretion and digestion, our enjoyment is due also to the consistency and other characteristics of the food which act upon the nerves of general sensibility. The glosso pharyngeal and lingual are also nerves of general sensation, and like the trigeminus in the nose act as guards against injurious substances. The intensity of the sensation of taste depends upon the “solubility and concentration of the substance and upon the degree of force with which it is rubbed in, as in tasting."

THROAT.

Limiting the term throat to the oro pharynx, we find its physiology of much importance, for here are located anatomical structures connected with the nose, mouth, and larynx, making their functions interdependent, so that the physiology of the pharynx is really that of the related parts.

Among the manv physiological functions which find their expression here are the voluntary ones of articulation and sucking. Deglutition and retching are for the most part involuntary and occur reflexly. The pharynx has important influence in articulation, especially in modulation of the voice, as in singing. In sticking, the base of the tongue is drawn downward and outward, and thus creates a vacuum, breathing in the meanwhile being carried on through the nose, between the acts of sticking and swallowing. The vital importance of maintaining free nasal respiration during infancy should be too well recognized to need further comment.

While deglutition is at the beginning a voluntary act, when once started it becomes involuntary. It is brought about reflexly by stimulation of the nerves of the pharynx, which happens normally by the presence of food, etc., or pathologically by any sensation of foreign substance in the throat. Thus, among other things, any abnormal dryness of the pharyngeal mucous mem¬brane, or enlargement of the lingual tonsil, or thickened secretion hanging in the throat may give rise to the ineffectual or “empty " swallowing which so often causes great distress. In swallowing normally, the action begins at the tip of the tongue, which is pressed against the roof of the mouth, the other sections following in order, the substance to be swallowed being thus forced backward into the pharynx. The anterior pillars of the fauces then come together, and, with the arched tongue, shut off the return to the mouth. Then the superior constrictors contract, forming an elevation (Passavant's cushion) across the posterior pharyngeal wall, which, meeting the elevated soft palate, shuts off the entrance to the naso pharynx. In paralysis of the velum, as after diphtheria, or in destruction or cleavage of the soft palate, the closure is incomplete, so that fluids and even solids regurgitate into the vault and even through the nose. In hypertrophy of the pharyngeal tonsil, which binders the full elevation of the velum, and in adhesion between the tonsils and the anterior pillars, which prevents the soft palate from ascending, the same insufficiency occurs. Following the contraction of the superior constrictors, the middle and inferior constrictors' of the pharynx act in¬ voluntarily and reflexly and force the object downward. At the moment of swallowing, the larynx is drawn upward and forward tinder the tongue, and the epiglottis is thus usually 2 forced over the laryngeal opening.

In retching, which precedes vomiting, there is contraction of the lateral walls of the pharynx so that they may meet in the median line. The center for vomiting 3 being near that of respiration in the medulla, practical use may be made of this knowledge in preventing vomiting during examination of the throat. By noticing this premonitory contraction of the fauces and directing the patient to breathe deeply and quickly, the tendency to retching may very frequently be stopped and the examination completed.

TONSILS.

While the physiology of these structures will be treated more fully in the section allotted to them, it seems desirable to emphasize here the important part they play as protective organs. It is now recognized that all the lymphatic tissue, whether in the form of simple collections of lymphatic cells scattered throughout the nose, Eustachian tubes or pharynx, or collected into prominent groups, as in the naso pharynx fauces, or at the base of the tongue, are germinating centers for leukocytes. That absorption is a special function of the tonsils, as asserted by some, is probably a mistake; for although made up of lymphatic tissue, they are not in direct connection with the general lymphatic system. Their peculiarly irregular surface favors the catching and retention of substances, and absorption can of course take place as easily here as through any mucous membrane.

We have spoken of the elevation of the soft palate in deglutition. As its elevation prevents the escape of food into the naso pharynx in swallowing, so its elevation prevents, and its relaxation permits, the passage of' waves of sound through the nose, and thus its action is of great importance in speaking. Particularly is this action of importance in singing, for the naso pharynx and nose are especially concerned in the production of overtones, which give fulness and character to the voice.

Too little attention has been given to the physiological functions of the uvula. While it is generally recognized that it assists in more securely stopping the entrance to the naso pharynx when the soft palate is elevated, I regard its most important function as that of acting on the edge of the velum like a weight on a drop curtain. In all the shades of tone the uvula is of great influence in causing the edge of the velum to fall more quickly, overcoming the tendency for its moist surface to adhere to that of the posterior pharyngeal wall. The rapidity of the actions of the soft palate in Singing or speaking can scarcely be appreciated until One has observed its movement directly, as in patients after the removal of the superior maxilla. That this function exists and is of practical importance can be readily recognized from the change in voice produced by too long or too heavy an uvula.

LARYNX.

The two important physiological functions of the larynx are those of protection of the delicate structures below and of voice formation. In addition, it has the function of regulating the amount of air in breathing, which is done reflexly, the glottis widening with each inspiration.

Of these, by far the most important to the whole economy is the function of protection. The contact of anything irritating with the sensitive structures guarding the larynx immediately causes them to contract, thus preventing its entrance; or, if it has gained admission, the sudden escape of air through the glottis tends to carry with it the offending substance, and the action is accom¬panied by a harsh sound (cough), due to the rough vibrations of the vocal cords. It is not only solid particles which thus call into action the protective function of the larynx, but also certain gases, such as ammonia and chlorin, called irrespirable gases; and even strong wind, whether warm or cold, act in a somewhat similar manner.

The larynx produces sound by throwing the column of expiratory and inspiratory air into vibration as it passes over the approximated edges of the vocal cords. This would give rise to sound of very limited nature, but it is so modified by the force of the current (volume), by the size of the opening (pitch), and by the influence of the surrounding cavities (quality), that the voice may become the most perfect of musical instruments. The action of the larynx is not like that of a pipe in the production of tone, for in order to give the low note, Do ( 64 vibrations), it would have to be some 8 feet long; neither is its action like that of a stringed instrument, for it would necessitate a cord many feet in length to produce this low note.' Its action closely resembles that of the hautboy, in which the sound is produced by a combination of pipe with a vibrating reed. The knowledge of this fact is made use of after laryngectomy by employing a reed in the artificial larynx to enable the patient to talk.

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