Intrinsic (Normal) Respiratory Sounds

The normal respiratory sounds consist of the vesicular sound and the bronchial sound.

The vesicular respiratory sound. The vesicular murmur resembles the sound produced when the letter 'V is whispered softly in a drawn-out manner. Its presence indicates that the lung con­tains air and that the alveoli are patent, since it originates from the air vortices that are formed where the terminal bronchioles open into the alveoli. This sound is normally heard throughout the respiratory area, except in the part where it is masked by the bronchial sound. The vesicular murmur is more clearly heard during inspira­tion; during expiration it may change its charac­ter and resemble the sound of the letter T. In large animals, when resting, the rate of air movement is reduced so that even the inspiratory vesicular sound is submerged. In the dog and cat, and in all young animals, the vesicular murmur is readily heard.

When respiratory frequency and/or amplitude are increased (hyperpnoea), or the breathing is laboured (dyspnoea), the vesicular sound is exag­gerated and is readily audible during both inspiration and expiration, as in excitement, pain­ful conditions and following physical exertion, etc. The vesicular sound is attenuated when the chest wall is thick, and when the air content of the lung is locally or generally reduced, e.g. in the early stages of pneumonia, passive conges­tion of the lung or when the lung is compressed by fluid in the pleural sac. When air is not enter­ing a portion of lung, so that not only the alveoli but also the bronchioles are devoid of air, the vesicular murmur is entirely absent, as in the later stages of pneumonia, pulmonary oedema and collapse of the lung. Shrill vesicular sounds are heard in active pulmonary congestion and hoarse sounds in early bronchitis, because swell­ing of the bronchial mucous membrane causes narrowing of the terminal bronchioles.

In cog-wheel respiration, the vesicular sound is interrupted and is heard in two or more parts, giving rise to a characteristic clicking sound, It is heard, as might be expected, when there is visibly jerking respiration, and may occur also when there is irregular expansion of lung due to either loss of elasticity of tissue, or where the bronchial mucous membrane is swollen to such an extent as to cause transitory obliteration of the lumen of the bronchioles during the late phase of expiration and the early phase of inspir­ation. Jerking respiration may be induced by fear, in which case the interrupted vesicular sound is heard on both sides throughout the area of auscultation. Localized interrupted vesicular sound occurs in tuberculous bronchopneumonia, and in fibrosis of the lung. Cog-wheel respiration is differentiated from chronic alveolar emphy­sema by being recognized during auscultation, as opposed to inspection.

Bronchial respiratory sound. This is blowing in character and resembles a long drawn-out gut­tural 'ch\ which commences and terminates abruptly. Normally it is always audible over the larynx and trachea. In small animals, and in very lean large animals, it is heard clearly, and in other large animals less distinctly, in the anterior part of the respiratory area where the larger bronchi are relatively near the surface of the body (so-called bronchial area). At this site it is known as a physiological bronchial sound. Apart from this, only the vesicular murmur is heard during auscultation of healthy lung. The bron­chial sound has an inspiratory and an expiratory component which are of approximately equal duration. In the so-called bronchial part of the respiratory area, the inspiratory bronchial sound terminates briefly before inspiration is com­pleted, so that a short pause precedes the subsequent expiratory bronchial sound, which is continued to the end of expiration.

When the lung contains less air, along with an increase in structural density, it acts as a better conductor of sound, so that the bronchial sound tends to supersede the vesicular sound over a variable extent of the respiratory area. Bronchial sounds are therefore heard beyond their normal situation in pneumonia, effusive pleurisy, hydrothorax and pulmonary neoplasia. (They do not extend beyond the normal area in bronchitis.) Bronchial sounds are heard also over air-containing cavities in the lung. In small breeds of dogs and in the cat, if the respiratory rate is increased because of excitement, even in the healthy animal, the bronchial sound will be superimposed on the vesicular sound throughout the respiratory area.

An amphoric sound is a type of bronchial sound resembling that produced by blowing into a large vessel possessing a small mouth. It is heard when a bronchus communicates with a large cavity in the lung (e.g. in gangrene of the lung), and also occasionally in pneumonia, if air in one bronchus rushes past the orifice of another that is not functioning. This sound is rarely heard in animals.

An indeterminate respiratory sound is one that is too faint to be classified as being either vesicu­lar or bronchial. Any condition causing attenua­tion of the vesicular murmur or bronchial sound may give rise to indeterminate sounds.

As opposed to this, respiratory sounds are said to be indistinguishable when they are diffi­cult to hear for some other reason such as exces­sive environmental noise, bronchial rules or loud peristaltic sounds.

Alternating respiratory sounds, i.e. vesicular during inspiration and bronchial during expira­tion, are occasionally encountered.

Adventitious (Abnormal) Respiratory Sounds

Abnormal respiratory sounds heard over the respiratory area originate from diseases of the bronchi, lungs, pleura or diaphragm, and include rales, emphysematous sounds, frictional sounds and peristaltic sounds.

Rales are sounds indicating the presence of secretion or fluid in the bronchi and bronchioles (exudate, transudate, blood, aspirated fluid). According to the viscosity of the secretion, rales may be moist or dry. They are inconstant, i.e. they may disappear for the duration of a few

respirations and reappear later. This is the result of movement of the mucus within the bronchial tree by coughing.

Moist rales occur when mucus of relatively low viscosity, or other fluid, is set in motion by air passing through it. They are bubbling in charac­ter (as when air is blown from the end of a tube under water). Accordingly as the rales originate in an alveolus, bronchiole or bronchus, they are classified as fine or coarse moist riles. The fine sounds are more unfavourable prognostically than the coarse sounds, because they indicate that the terminal parts of the respiratory tract are involved in disease. Moist rales occur in various forms of bronchitis, pulmonary haemorrhage, bronchopneumonia and inhalation of fluid.

Dry rales are heard when air is being forced through a bronchial tube which is partially con­stricted, either by dry tenacious mucus or by severe swelling of the mucous membrane. Fine threads of secretion or mucus are formed, which are set vibrating by the current of air. Dry rales vary in pitch according to the diameter of the bronchial tube in which they originate. They are heard as humming, rattling, whistling, crack­ling or squeaking sounds, or those produced by movement of a tightly stretched piece of paper. Dry rales occur in the early stages of acute bronchitis, in chronic bronchitis, spasm of the bronchial muscle and pulmonary neoplasia or tuberculosis when there is distortion of the bronchi.

Rales are occasionally very loud, strong, ring­ing and clearly audible. They originate in severely infiltrated tissue, which explains the good conduction of the sound. As opposed to this, rales that originate in air-containing pul­monary tissue, e.g. in bronchitis, are considerably softer in tone and therefore more difficult to hear.

In order to make occasional or very faint rules audible, it may be necessary to induce hyper­pnoea by occluding the animal's nostrils for a short period, and then to auscultate during the deep breathing that follows the removal of the obstruction.

Crepitant rales (crepitations) are crackling sounds heard only during the later part of the inspiratory phase. They are produced when the bronchial mucosa is sufficiently swollen, or exu­dation has affected the alveoli, so that the oppos­ing walls become adherent to one another and have to be parted by the stream of incoming air. The sudden separation of the adherent mucous membrane causes a low-pitched crackling sound, which can be simulated by rubbing a tuft of hair held between the fingers, close to the ear, or by separating the opposed, moistened tips of the thumb and forefinger close to the ear. Care is necessary to avoid friction between the chest-piece of the stethoscope and the coat of the animal, otherwise confusing sounds are pro­duced. This can be largely avoided by using an instrument with a rubber rim on the chest-piece, which should be held firmly against the chest wall. Crepitant rules occur in bronchitis, in the early stages of pneumonia, during the resolution stages of inflammation, and in pulmonary oedema along with bubbling sounds.

Emphysematous sounds are harsh and crack­ling, and are heard during the whole inspiratory phase and to a less obvious degree during expira­tion. This sound simulates that produced by crushing a sheet of soft paper into a ball. It occurs in chronic alveolar emphysema, in which case it is widespread, and in acute alveolar emphysema and oedema, when fluid sounds may also be detected.

Frictional sounds in the respiratory area are associated with the pleura or pericardium. Nor­mally during the movements which occur in respiration, the visceral and costal pleurae glide silently over each other, since both membranes are smooth and are lubricated by a clear lymph-like fluid. When the two opposing surfaces are dry and roughened, however, rasping or scraping sounds are heard, and these are constant, occur­ring with each respiration. They can be simulated by rubbing together two pieces of dry leather or by pressing a finger against the ear and scratch­ing it with a fingernail of the other hand.

Frictional sounds are associated with the early pre-exudative stage of pleurisy and pericarditis. Pericardial friction sounds can be differentiated from those of pleural origin by noting their position of origin, and that they are not related to respiratory frequency and movements. In the respiratory area frictional sounds may easily be confused with dry rales. The following points will serve to distinguish between them: rales are inconstant, being heard first at one place and then at another; following a cough, which in this case is strong and not painful, they may disappear for a varying period. Frictional sounds are con­stant, although not continuous, being heard in the same phase of respiration, more usually during inspiration; following a cough, which is usually painful and suppressed, they are still present. Pleurisy is in many cases a complication of pulmonary inflammation, therefore, rales and crepitations may accompany frictional sounds. Because of the pain that is associated with the early phase of pleurisy, the respirations, particu­larly in the horse, will show altered features, becoming characteristically abdominal. The dis­appearance of frictional sounds may mean complete resolution, exudation of fluid which lubricates the inflamed membranes and separates them, or the development of pleural adhesions. Rules and frictional sounds may be so volumi­nous that their origin can be perceived as a rasping, or thrill, when the hand is placed on the thorax.

During auscultation of the lung, sounds un­connected with respiration may be heard. They have a distracting effect and are sometimes mis­taken, particularly by the inexperienced clinician, for respiratory sounds. To this category belong, for example, sounds that arise from the swallow­ing of food, groaning, contraction of muscles, trembling, abnormally loud cardiac, and in par­ticular peristaltic sounds. The last, on account of their volume, are frequently heard during auscultation of the lung; they are sometimes mistaken for rales. Such peristaltic sounds are more normally heard over the lung area on the left side in horses and cattle; in the horse they are caused by movements of the colon and in the ox by movements of the reticulum. The basis of differentiation is that intestinal sounds are dis­tant sounds, they are splashing and rumbling in character and they are not related to any parti­cular phase of respiration but occur indepen­dently of it. Rales can be determined to coincide with the respiratory movements. The functional sounds, originating in segments of intestine that have passed forwards into the thoracic cavity as the result of hernia or rupture of the diaphragm are of particular diagnostic significance.

Succussion sounds are splashing sounds, caused by agitation of fluid which has a free surface at which movement can take place. They are heard in pyopneumothorax (pus, with overlying air, in the pleural sac). When such fluid is set in motion by lung movement, or when a small animal is picked up and gently shaken, the splashing may be audible. In the last instance movement of fluid and gas in the digestive tract will produce similar sounds.

Special Methods for Examination of the Thoracic Respiratory Organs

Radiological Examination

For diagnostic purposes radiological exami­nation of the chest is a practical proposition in the dog and cat, also in calves, sheep, goats and pigs, and may reveal essential evidence of respira­tory or thoracic disease. Similar results can be obtained in foals or larger animals only by the use of high-output X-ray machines, which are not in general use. Fluoroscopic examination of the chest region makes it possible, in suitable cases, to assess the functional movements of the various respiratory components in this area, including the ribs and diaphragm.

The value of radiological examination as an aid to establishing a diagnosis of chronic bron­chitis, or bronchiectasis, in the dog or cat is un­certain unless a suitable contrast medium is used (bronchography). The introduction of a radio-opaque medium into the bronchial tree involves anaesthetizing the subject and inserting a polythene catheter into the trachea and each dependent bronchus in turn to a selected point during bronchoscopy. Adjusting the posture of the animal will then assist the distribution of the small quantity of radio-opaque material required. In this way the incomplete filling of some bronchi, along with dilatation of the terminal part of the trachea and main bronchus, which are characteristic of chronic bronchitis, are revealed.

In bronchopneumonia the radiograph may reveal a variable picture which may include patchy variations in density, distension of major blood vessels in the perihilar area and atelectasis, which may involve the base of both lungs or the ventral parts of the lobes. The radiographic pic­ture in interstitial lung change, a frequent sequel to diseases such as canine distemper and specific pneumonias caused by virus infection, is one of either peribronchial cellular proliferation or thickening of interlobular septa with areas of collapse. Spontaneous or other forms of lung collapse are readily recognized by marked in­crease in density of the whole or part of a lung, which is also reduced in size and is seen not to fill the pleural sac. The presence of fluid within the pleural cavity, encountered in some types of pleurisy (nocardiosis and tuberculosis in the dog), neoplasia and hydrothorax, produces a charac­teristic radiographic picture. When exposures are made with the animal in standing posture, the main features revealed are partial collapse of the lung with increased density throughout the ventral portion. In pneumothorax, radiography will show an air pocket at the highest point of the pleural cavity, with the posterior aorta form­ing an arch at the upper posterior part. Mediastinal displacement is not a marked feature in unilateral lung collapse or pneumothorax in the dog, at least, because air passes through the mediastinum so that pressure tends to equalize on both sides.

Radiography is particularly valuable as a diag­nostic aid in diaphragmatic hernia, making it pos­sible to recognize an abnormal diaphragmatic shadow or, in some cases, its complete absence. Other possible radiographic features of this con­dition include areas of increased, or decreased, density within the thorax, resulting from the presence of the liver and/or portions of the digestive tract in this abnormal situation. The administration of a barium meal, although un­necessary in most instances, will confirm the abnormal position of the hollow viscus.

Radiological examination will ensure confir­mation of intrathoracic neoplasia. Routine screening of small animals has led to re-evalua­tion in many unsuspected cases of respiratory tract tumours. Primary neoplasms involve either the lungs or the mediastinum, and when of moderate or large size produce an area of in­creased density and cause a variable degree of organ displacement. Secondary pulmonary neo­plasms are more common and, originating from a variety of sources, may be associated with appropriate clinical signs. Radiographically it is usual to ascertain that metastatic tumours involve both lungs producing a variable number of localized areas of increased density through­out the lung fields (Fig. 124).

Direct radiography will reveal radio-opaque foreign objects when they obstruct the thoracic portion of the oesophagus. The presence of objects in a similar situation, which are not revealed in this way, is usually disclosed by means of oral administration of a barium-containing capsule or draught, the former will be retained immediately anterior to the object, while the latter will outline it by forming a surface film. Other oesophageal conditions which are revealed in this way include achalasia.

Paracentesis

Paracentesis of the thorax is of value when the presence of fluid in the pleural sac is suspected. The procedure is performed by means of a suitable sterile needle and syringe. The site for insertion of the needle is either the sixth or seventh intercostal space below the level of the fluid (it is best to select a point below the level of the costochondral junction). The needle should be inserted with care in order to avoid injury to the pericardial sac. Aspiration of fluid is effected by pulling on the piston and filling the syringe.

Examination of the aspirated sample of fluid will reveal its gross and microscopic features and thus assist in diagnosis. In haemothorax, the blood is fluid at the time of withdrawal but may clot on exposure to air unless an anticoagulant is added. As a rule haemothorax of significant proportions is accompanied by other clinical signs indicating the presence of acute haemorrha-gic anaemia. In hydrothorax, the recovered fluid may vary in character from clear serous to opaque depending upon the number and types of tissue cells present. Clinical signs of general oedema, caused by congestive heart failure or hypoproteinaemia, or extensive pulmonary neo-plasia, may be associated features. In cases of exudative pleurisy the causal organism may be revealed by microscopic or cultural examination (nocardiosis and tuberculosis).