SECTION III.. Respiratory Apparatus.

RESPIRATORY APPARATUS.

CHAPTER I. EXAMINATION OF THE RESPIRATORY APPARATUS.

From the clinical standpoint a study of the respiratory apparatus implies the examination of the nostrils, nasal cavities, frontal and maxillary sinuses, larynx, trachea, and, for the purpose of ascertaining the condition of the lungs and pleura, of the chest.

=Nasal cavities.= Examination of the external portion of the nasal cavities is extremely simple. The observer notes the degree to which the orifices are dilated, the frequency of the respiratory movements and the condition of the muzzle. He may find various eruptions, crusts due to discharge, etc., and will remark any peculiarities presented by these. The depths of the nasal cavities can only be examined through the nostrils to a very limited extent; but the condition of the pituitary mucous membrane, its degree of vascularity, and the existence of ulcerations or of vegetations can be observed.

Digital examination is sometimes useful in discovering the condition of the lower portions of the turbinated bones. The electric light does not greatly assist the observer, on account of the narrowness of the air passages. On the other hand, examination of the face, and palpation and percussion over the region of the frontal sinuses is of considerable value. By inspection, one discovers deformity caused by tumours, by ossific inflammation, or other lesions; and detection is rendered easier by the fact that deformities are usually asymmetrical, only occurring on one side.

Palpation reveals the degree of resistance and flexibility of the external bony wall as well as the condition of the subcutaneous tissues.

Percussion sometimes discloses absolute dulness, due to tumours of the mucous membrane, of the turbinated bones, or of the bones of the face.

The pharyngeal portion of the nasal cavities is difficult to reach, but can be examined by passing the hand, palm upwards, into the pharyngeal cavity, when the fingers may be slipped behind the soft palate and thus introduced into the posterior nasal chamber. The animals should first be very carefully secured and a strong gag introduced into the mouth.

=Sinuses.= Frontal sinus.—The frontal sinus occupies the greater part of the anterior cranial region and the summit of the head, extending from the highest point of the poll as far forward as a line drawn between the two orbits. Above, it directly communicates with the sinus of the horn core. In this upper region, where it abuts on the sinus of the opposite side along the median line, it is of greatest size. Below, on the other hand, it is very narrow, much broken up and incompletely divided into a series of cells, by thin, bony plates running in all directions.

It is in direct communication with the nasal cavity.

The frontal sinus, then, occupies all the supero-lateral portion of the cranial box, which is thus provided with a double wall. At one point, however, over a lozenge-shaped area, the cranial cavity is only protected by a single wall. It is in this region that the slaughterman strikes the animal when killing it.

The frontal sinus may be examined by inspection and palpation. Inspection sometimes reveals deformity of the external wall of the sinus. Such deformity, however, is rare, and Moussu has only observed it in two cases of tuberculosis of the bones forming the cranial wall.

By percussion one detects abnormal sensibility, and partial or complete dulness over certain areas.

Maxillary sinus.—The maxillary sinus occupies the whole lateral region of the face, from the inferior extremity of the maxillary spine as far as the sub-orbito-palatine region. In front its external wall is very solid, but behind, below the orbit, is extremely thin. Externally the sinus is largely protected by the anterior insertion of the external masseter muscle, a fact which explains how rarely it is injured.

=Larynx.= In consequence of its deep situation, the larynx can scarcely be examined except by inspection, external palpation, internal digital palpation, and auscultation.

External examination presents no difficulty, and enables one to detect lesions around or near the larynx.

Palpation reveals the existence of œdematous swellings, enlargements of the retro-pharyngeal lymphatic glands, inflammatory engorgements, etc.

Internal digital examination, like examination of the pharynx, can only be performed after very firmly fixing the animal in position, and inserting a gag in the mouth.

The hand is introduced, palm downwards, and passed as far as the pharyngeal cavity. The index finger can then easily be slipped into the glottis. Exploration must be effected rapidly and without violence. It reveals the condition of the glottis, the presence, position and form of growths like myxomata and of new tissues, due to the presence of actinomyces, as well as tuberculous vegetations or ulcerations.

By auscultation we discover the presence of normal or abnormal laryngeal sounds—roaring, whistling, or bubbling sounds, etc.

=Trachea.= The trachea may be examined by palpation and auscultation.

Palpation reveals the degree of sensitiveness, abnormalities in position or form, the presence of peripheral inflammations, fractures of rings, etc.

Auscultation indicates whether the tracheal sound be normal or otherwise, or accompanied by abnormal sounds, like mucous râles, or by pathological sounds conveyed from the chest.

=Thorax.= The thorax can be examined by inspection, palpation, percussion, and auscultation.

By inspection we discover whether the formation of the thorax as a whole is normal, or whether there exist congenital or acquired deformities, asymmetry like that produced by pneumo-thorax or deviations of ribs from the normal line, etc. One also notes the breathing movements, the manner in which the sides expand and contract, the respiratory rhythm, and any special peculiarities of inspiration or expiration.

Palpation reveals the degree of sensitiveness of the thoracic wall and of the intercostal spaces, the existence of more or less extensive local œdematous infiltration, and the presence or disappearance of thoracic conditions like hydro-thorax.

Percussion indicates the degree of sonority of the chest in different parts. It can either be practised directly with the hand or through the medium of a pleximeter. The latter method is preferable when dealing with fat animals. Percussion, however, gives slightly different results, according to the degree of fatness of the subjects. It should be practised both in a vertical as well as in a horizontal direction.

At all points where the muscles are thick or well developed the results produced are negative, in the sense that only a dull sound is obtained. This is the result obtained in auscultating the areas marked =1=, where one meets with the ileo-spinal and common intercostal muscle, and in that marked =4=, where the olecranian muscles are encountered (Fig. 166). Over the middle and inferior zones, however, the results are much more instructive.

On the right side percussion of the middle zone gives, under normal conditions, a clear sound and perfect resonance from above downwards, and from in front backwards, between the fourth intercostal space and the ninth rib. Beyond this point lies the liver, which gives a partial dull sound, and absolute dulness from the ninth to the twelfth rib, in consequence of its position, and of the projection of the diaphragm towards the thoracic cavity.

Percussion of the inferior zone produces less marked resonance, which diminishes more and more towards the base, in consequence of the thinness of the pulmonary lobes at this point. This resonance does not extend as far as the hypochondriac region, because the lower part of the abomasum insinuates itself beneath the costal cartilages and causes a region of dulness.

On the left side percussion gives precisely similar results, except in the upper portion of the middle zone. Beyond the ninth intercostal space the sound changes, and has a tympanic character; because here the anterior and upper portions of the rumen are encountered, as they are lodged beneath the hypochondrium. Below, the sound is dull, on account of the gastric compartments generally being full of food.

Certain trifling modifications of this normal condition may be noted, depending on the degree of fatness or thinness of the subjects. The pathological changes which may occur are as follows:—

A tympanic sound, with or without metallic character, may be found at a point where normally one would expect a clear sound (pneumo-thorax, diaphragmatic hernia). A dull sound may be met with in the same regions, all resonance being lost (pneumonia, broncho-pneumonia, pleural exudate, etc.). Partial dulness and partial loss of resonance may occur in regions which ought to give a resonant sound (deep pneumonia, tuberculous lesions, the presence of echinococcus cysts, etc.).

Auscultation—i.e., examination by means of the ear—is the most valuable method of discovering and localising pulmonary, pleural, or cardiac lesions.

Various sensations are conveyed to the ear, depending on the method in which the normal or pathological sounds are produced.

The deductions to be drawn as regards the nature of existing disease are based on the intensity, character, duration, and special attributes of the sounds noted.

Direct auscultation is the most certain method, but the ear cannot be applied with equal facility at all points. Under such circumstances a simple or binaural stethoscope, or the phonendoscope, may be used with advantage.

To properly appreciate the sounds heard it is essential to be exactly acquainted with the relation between the lung and thorax. On the left side (Fig. 60) the anterior pulmonary lobe occupies the space between the first and fourth ribs, in front and above the base of the heart. The middle, or cardiac, lobe covers the left upper and postero-lateral part of the heart from the fourth to the sixth rib. The posterior lobe occupies all the region beyond the sixth rib as far as the twelfth.

On the right side the arrangement is similar, but the anterior lobe and the cardiac lobe are more developed (Fig. 62).

Under ordinary circumstances the extensive movement of the lung which occurs during inspiration produces a special sound known as the respiratory or vesicular murmur. Contrary to what has been written, and said, this sound in animals possessing absolutely sound lungs ends with inspiration. Expiration is silent, though it is easy to estimate its duration.

In auscultating the lung, we may distinguish four zones, a superior zone, a middle zone, an inferior zone, and a scapular zone.

The superior zone is bounded by the vertebro-costal gutter, descends approximately as far as the inferior line of insertion of the common intercostal muscle, and extends from the summit of the scapula in front to the hypochondrium behind.

Auscultation of this region through the ileo-spinal and common intercostal muscle will always reveal, except in very fat animals, the vesicular murmur to a point as far back as the eleventh intercostal space. Nevertheless, this vesicular murmur is relatively feeble, and becomes imperceptible beyond the eleventh rib.

The middle zone comprises the most convex portion of the ribs, and at this point the wall of the thorax is thinnest, while the lung below is thickest.

For these reasons the vesicular murmur is heard at its maximum intensity at this point. Towards the upper and lower limits of this zone are found the great bronchial divisions, so that auscultation should always be practised with the greatest care at this point. The middle zone occupies approximately one-third of the total depth of the thorax. The vesicular murmur becomes weaker as one passes backwards, and finally disappears at a considerable distance from the angle of the hypochondrium, following a curved line the convexity of which is directed forwards, and which is continuous with that limiting the upper zone.

These peculiarities are due to the anatomical arrangement and mode of insertion of the diaphragm on the internal surface of the hypochondrium.

The inferior zone is very limited, and corresponds externally to the inferior third of the thorax, and topographically to the cardiac lobe or middle lobe of the lung and to the inferior portion of the posterior lobe.

As these pulmonary lobes are of comparatively slight thickness, the vesicular murmur is feeble. It can be heard over a trapezoidal space, forming a prolongation of the middle zone, but not below in the region of the sternum or pectoral muscles.

The fourth zone extends over the mass of the olecranian muscles. It is of triangular form, in consequence of the inclination of the scapula and humerus. Except in very fat animals the vesicular murmur is readily audible through the muscular mass on the right side better than on the left, on account of the development of the right anterior pulmonary lobe.

On the left side the beating of the heart is heard above the pulmonary sounds.

Clinically one may hear an exaggeration of the ordinary respiratory murmur whenever the lung is actively exercised, as, e.g., immediately after trotting. This exaggeration, however, is often pathological. It is known as “juvenile or supplementary respiration,” when due to the fact that some other portion of the lung is not acting.

The respiratory murmur may be lessened in certain morbid conditions, such as emphysema and congestion of the lung, and may completely disappear in pneumonia or broncho-pneumonia, a fact which is even of greater significance.

In various pathological conditions the respiratory murmur may also be modified. On the other hand, the movement of air in the bronchi also produces various sounds of importance.

A number of different bronchial sounds may be distinguished; these include both inspiratory and expiratory sounds, for sometimes an expiratory sound may become audible and clearly appreciable, or may acquire characters of the greatest importance.

The inspiratory sound may be strong, rough, rasping, painful, moist or rattling. The pathological expiratory sounds may vary between audible, strong, rough, prolonged, or rattling. The varieties of souffle, or rattle, are the tubal souffle of inspiration or expiration (met with in pneumonia or broncho-pneumonia); the soft, deep-seated pleuritic souffle (peripneumonia); the continuous cavernous souffle (met with in tuberculosis); the broad amphoric souffle, in which the vibrations are extensive and of metallic character (met with in pneumo-thorax).

As to the varieties of râles which usually accompany these souffles, they may all be met with in tuberculous animals, and comprise crepitant and sub-crepitant, mucous, cavernous, snoring and sibilant râles.