Auscultation of the lungs

Auscultation is an objective method of study based on listening and evaluation of acoustic phenomena, which naturally occur in the functioning organisms.

The difference between auscultation and percussion is that on percussion we produce vibrations of the tissues artificially, on auscultation we listen to the sounds produced in the organ due to the changes of the tissue tension on their functioning. As a result, the sounds obtained on percussion are loud enough to be heard at a distance. Auscultation sounds are weaker and can be heard when applying the physician's ear to the patient's body, or with the help of sound-conducting tubes (stethoscopes).

As to the way of listening two types of auscultation are distinguished:

1) direct auscultation performed applying the ear to the patient's body;

2) indirect auscultation performed with the help of a special tube, a stethoscope (from Greek sthetos - chest, scopeo - look).

Thus, indirect auscultation uses an instrument. It has a number of advantages: the funnel of the stethoscope is smaller than the auricle of the ear, this allows listening to the acoustic phenomena at a smaller area. It is more convenient prom hygienic perspective. It allows listening to the areas inaccessible for the ear (supraclavicular, axillary).

Auscultation rules

1. The chest of the patient should be bare as the shuffling of the clothes may mix with the sound.

2. The examination room should be warm and silent.

3. The stethoscope should be applied to the body tightly, with the whole edge of the funnel (not with its portion as, first, it can cause pain, second, the air between the body and the funnel increases the sound by resonance and changes it). Sliding of an untightly applied stethoscope may also produce accessory sounds.

4. It is not necessary to use excessive force to apply the stethoscope. It can cause pain and hinder vibrations of the chest wall in the studied area, in this way weakening conduction of the vibrations from the underlying tissues to the air and the ear.

5. It is not necessary to hold the tube of the stethoscope with the hand as the minute motions of the holding fingers can add sounds.

6. It is necessary to use one and the same stethoscope. Various stethoscopes and phonendoscopes are available for indirect auscultation. This method allows avoiding some disadvantages of direct auscultation mentioned above, besides the instrument aids conduction of the sound to the physician's ear and limits the studied area.

Stethoscopes, which can enhance acoustic phenomena, have been made recently. They are termed phonendoscopes. Their shape can be various, but all of them can enhance the sound. The terminal portion of a phonendoscope is a metal cavity covered with a membrane. This portion is applied to the studied area. The acoustic phenomena in one or another organ (heart, lungs) are conducted to the membrane, which starts vibrating. The cavity covered with the membrane enhances the sound. The enhanced sound is conducted through the tubes.

Physical grounds of auscultation are similar to percussion. For better understanding of the mechanism of auscultation phenomena and diagnostic assessment, some knowledge of physical phenomena is necessary. Sound is known to propagate owing to alternations of condensed and rarefied air. When a body deviates from the balance position, the adjacent layer of air is compressed and gets denser. But owing to high elasticity this layer rarefies rapidly and gets to the initial state. While rarefying the volume increases and exercises pressure on the following layer, which is in turn gets condensed and decreases the volume. Rarefaction and increase in volume in the second layer causes compression and consolidation of the third layer. Alternations of condensing and rarefaction propagates from the source until the air layer in the ear condenses, rarefaction and consolidation of the air in the auditory canal cause vibrations of the tympanic membrane, which transmits the vibrations to the auditory nerve. Excitation of the auditory nerve causes sensation of the sound. As sound waves propagate rectilinearly in all directions, each air layer has a shape of a hollow sphere, the whole mass of the air conduction the sound can be imagined as a number of concentric spherical layers with the source in the center. With the distance from the source, the volume of each sphere increases, the degree of consolidation and rarefaction decreases from layer to layer. Sound loudness decreases with the distance from the source. A sound-conducting tube can prevent weakening of the sound. The dense walls of the tube and poor ability to vibrate prevent energy scattering and the energy is used to condense the air in the tube itself. The air levels when condensing and rarefying have the shape of segments of sphere (not sphere). The sound which reaches the ear is not weakened.

In the lungs, the role of sound-conducting tubes is played by the bronchi. The air columns in the bronchi are the medium carrying vibrations caused by percussion strikes or the lungs themselves to the chest wall. These vibrations cause the vibrations of the chest wall, which are conducted to the surrounding air and to the ear of the physician. But the conditions in the lung are not entirely favorable as elasticity of the bronchial walls and their ability to vibrate provide propagation of the sound wave in all directions. Due to this fact the amplitude of vibrations decreases by the moment it reaches the chest wall and the sound is considerably weakened.

These conditions change with the tissue morphology. Thus, at consolidation (alveoli filled with exudate in pneumonia, consolidation of the lung tissue around the bronchi) the lung tissue being less capable to vibration then the bronchial wall slows down the vibrations of bronchi, in this way less energy propagates aside in the air column in the bronchi. Thus, the sounds, developing in various departments of the respiratory system, are better conducted to the chest wall through the consolidated lung are louder.

The air column in the bronchus can play a role of resonator besides conducting the sound. Resonance is sound straightening, if the conducting medium has similar frequency of vibrations. Coincidence of the vibration frequency in the conducting medium and that of the sounding object is possible only with a definite mass of the conducting medium or with a definite length of the tube containing this medium, because the length of the vibrating object is inversely proportional to the frequency of vibrations. Sounds carried by the bronchi are noises. The air columns in the bronchi can strengthen only those sounds, which have the respective frequency depending on the length. As the sound is conducted through many bronchi of various lengths at the same time, each bronchus strengthens several sounds. In a healthy lung the resonance does not influence the sound loudness heard on auscultation and percussion, because the air filling the lungs absorbs the sound. Resonance occurs in lung consolidation, which is due to reduction of the ability of a denser tissue to absorb sound. The sound increased with resonance reaches the ear and is heard without weakening.

Thus, lung tissue consolidation prevents sound weakening, on the one hand, and provides resonance action, on the other hand. Due to resonance one or several high pitches, which are a part of light sound, increase; this allows determining the pitch. Sometimes this gives the sound a metallic shade (a characteristic feature of the sounds from a consolidated lung). As the air layer in the bronchus is the medium, which conducts the sound, all auscultation phenomena can disappear when the bronchus is obturated by mucus or a foreign body. In other words, potency of the bronchus is a necessary condition for successful auscultation of the lungs.

Resonance can develop not only in the lung but also in the cavity surrounded by a consolidated lung tissue.

Everything told about the lung tissue consolidation is true both for percussion and auscultation. The difference is in the fact that percussion energy is applied from outside as a percussion strike, on auscultation it develops within the lung as a result of changed tension in the lung tissue at respiratory maneuvers. The depth of penetration of a percussion strike is about 3—5 cm, auscultation can elicit deeper changes. In other respects, percussion and auscultation resting on the same physical grounds, complement one another because both deal with the phenomena due to the physical properties of the thoracic organs. The apparatus, which receives the phenomena, is the physician's ear.

To understand some acoustic phenomena in the respiratory tract it is necessary to know some physical phenomena, which take place on movement of gases or fluids in the tubes.

If a tube, carrying gas or fluid, has a narrowing, the gas or fluid has to leave the wide portion of the tube through the narrowing to the wider portion, circulations of the gas or fluid occur in the place of narrowing. If the tube walls are elastic, this circulations cause vibrations, that is sound in the place of narrowing. This sound is called stenotic (stenosis - narrowing).

The sound loudness depends on the degree of narrowing and the velocity of the flow. The greater is the narrowing and the higher is the velocity, the louder is the sound; moreover, a definite velocity of the flow producing the sound corresponds to each degree of the tube narrowing. Thus, in considerable narrowing the velocity may be lower to produce sound.

Main breath sounds may be divided into two types: vesicular and bronchial breath sounds.

When listening over the larynx (lower portion of the neck), trachea and large bronchi (upper portion of the chest), respiratory sound resembling "h" sound is heard, expiration is louder and longer than inspiration. This sound is produced in the larynx when the air passes trough the fissure of the glottis due to air circulation above the vocal cords at breathing in and under the vocal cords at breathing out. As the fissure of the glottis is narrower at breathing out than at breathing in, the sound produced will be rougher and longer. This is the so-called laryngotracheal or bronchial breath sound (respiration).

The sound overt he rest of the chest is completely different. It is a soft, blowing sound resembling "f' sound. This sound is stronger and longer on breathing in and weaker on breathing out. At the beginning of inspiration, in its first third, this is weak and poorly heard, later it becomes stronger and weakens with the beginning of breathing out and is heard only in the first third of expiration. This respiratory sound is called vesicular breath sound (respiration). Vesicular respiration is produced in the lung parenchyma when the air enters the alveoli and their walls get strained.

Vesicular respiration occurs when the lungs expand during inspiration. The alveolar wall rapidly transits from a weakened state, in which it was at the end of expiration, to a strained state. Vibrations, producing the sound, occur as a result. A great number of alveoli vibrate at the same time and all alveoli expand consequently. As a result of summing the sounds, a pulmonary sound of vesicular respiration is heard. During breathing in due to alveoli collapse the tension in the walls rapidly decreases, their ability to vibrate decreases, that is why the respiratory sound is heard only at the beginning of breathing out, but the walls of the alveoli preserve some degree of tension.

Physiological properties of vesicular breath sound. Vesicular breath sound is better heard on the anterior surface of the chest. It is less intensive in infer-lateral portions of the lung (lower portion of axillary area), lower borders of the lungs (decreased mass of the lung tissue). This respiration is weak over the lung apices (small volume of the lung tissue, thick muscular layer on the back, low respiratory mobility). Vesicular breathing is different over the both halves of the chest: on the left it is clearer (proximity of the gastric air sac), expiration is more pronounced on the right (due to wider and shorter main bronchus promoting better conditions for conducting bronchial respiration from the larynx).

This difference in expiration intensity is well noticed over the lung apices. On the right apex, expiration is longer than that over the left one (the right apex is closer to the trachea, the right apical bronchus is more horizontal). Mixed (bronchovesicular) respiration can be heard over the right apex. Increased vesicular respiration with a well-heard expiration is observed in children aged 12—14 (due to a thin elastic chest and relative proximity of the bronchi).

Changes of vesicular respiration can be quantitative and qualitative. Quantitative changes of vesicular respiration manifest by weakening or strengthening of the respiration. Physiological weakening of vesicular respiration is observed in thickening of the chest wall due to abundant development of its muscles or increased fat amount. Main causes of weakened vesicular respiration are difficult air passage to the lungs; insufficient expansion of the lungs at breathing in; an obstacle for the sound conduction to the ear of the physician.

The difficulties in the air passage to the lungs may be due to narrowing of airways with a foreign body, tumor or compression of the larynx, trachea, bronchi by an external lymph node, tumor, scar. Weakening of vesicular respiration may be caused by decreased expansion, alveolar wall tension with lower vibration amplitude. When the larynx and trachea are narrowed, vesicular respiration is evenly weak in the both halves of the chest. In bronchus narrowing, weakened vesicular respiration is heard over the portion of the lung supplied through the narrowed bronchus.

In complete obstruction to the bronchus with a foreign body or a tumor respiration is not heard in the respective portion of the chest.

Weakened vesicular respiration due to insufficient expansion of the alveoli on inspiration is observed at some lung diseases, i.e. emphysema due to decreased respiratory excursion of the lungs and reduction of their elasticity; at focal pneumonia in the area of inflammation due to exclusion of the alveoli from the act of respiration; at the initial stages or resolution of lobular pneumonia when the alveoli are not filled with dense infiltration, but the tension of the walls, saturated with exudates, is decreased.

Weakened vesicular respiration is observed at reflex reduction of respiratory mobility of one half of the chest with pain appearing on breathing (in dry pleurisy, rib fracture, intercostal neuralgia). The alveoli of the respective lung expand less than normal hence the vesicular respiration on this half is weaker.

A frequent cause of weakened vesicular respiration is obstacles for conduction of the respiratory sound to the ear of the physician. They are accumulation of air or fluid in the pleural cavity; displacement of the lung from the chest wall with a thickened pleura or tumor; considerable thickening of the chest (edema, subcutaneous emphysema).

Increased vesicular respiration can be physiological or pathological. It is observed in cases when alveoli expansion on breathing in is more forceful.

Physiological strengthening of vesicular respiration develops on physical exercise, increase of body temperature, at a thin chest. Strengthening of respiration over one lung is observed when respiration in the other lung is absent (compressed with pleural effusion or pathological process in it). This increased breathing is termed compensatory.

Pathologic strengthening of vesicular respiration can occur at the phase of expiration or at the both phases: inspiration and expiration. Increased expiration depends on strengthening of the air passage through the small bronchi when their lumens are narrow (bronchospasm, inflammatory edema of the mucous membrane).

Qualitative changes in vesicular respiration. Rough breath sounds appear when the lumen of the bronchus is unevenly narrowed, as a result, the sound of the air passing through the narrowed bronchi with a changed wall is mixed to vesicular respiration.

Vesicular respiration with prolonged expiration: not only inspiration and the initial stage of expiration but also the whole phase of expiration are heard. The causes are similar to those of rough sounds.

Interrupted respiration is vesicular respiration which is not continuous as usually, but consists of separate short inspirations interrupted by short pauses. This may be due to contraction of the respiratory muscles (fatigue, muscular trembling) and in this case is heard over the whole surface of the lung. In the both cases interrupted respiration appears because the air enters the alveoli in several movements.

Pathological bronchial respiration. If bronchial respiration is heard over one area of the chest besides the areas where it is heard in healthy individuals, this is called pathological and suggests the changes in the physical properties of the lung.

Pathological bronchial respiration appears when vesicular respiration is absent and bronchial respiration is conducted to this particular area from the place of its origin. Main condition for this is consolidation of the lung tissue due to filling the alveoli with inflammatory exudate (hepatization stage of lobular pneumonia), blood (lung infarction), compression atelectasis. In all these conditions vibrations of the alveolar walls are absent and the dense lung tissue becomes a good conductor for the sound waves of the laryngotracheal respiration to the chest surface. Consolidation of the lung can result from replacement of the lung tissue with a connective tissue (pneumosclerosis, cornification of the lobe).

Pathological bronchial respiration may be of various intensity and timber which depend on the degree of consolidation and location in the lung. A loud bronchial respiration is heard when there is a large area of dense pulmonary tissue. In this case the timber of the bronchial respiration is higher (this can be heard in the 2^nd stage of lobular pneumonia). More silent bronchial respiration with low timber is heard when only a segment of the lung or its deep portion is dense (focal pneumonia). Especially silent low-timber bronchial respiration is present in compression atelectasis.

Pathological bronchial respiration can be hard when a free cavity or abscess joined with the bronchus are present in the lung. Consolidation of the lung tissue around the cavity facilitates better conduction of the sound waves to the surface of the chest. In this case the character of bronchial respiration can be distinctive (either amphoric or bell breath sounds). These types of bronchial respiration are observed when the following are present: a considerable size of the cavity (>5—-6 cm), smooth inner surface of the cavity, moderate degree of filling with pus.

Amphoric breath sounds (from Greek amphora - a vessel with a narrow neck) is a low empty sound resembling that which is produced by forceful blowing over the neck of an empty bottle. It appears when the walls of the cavity are smooth and it communicates with a large bronchus. The resonance facilitates appearance of accessory high overtones in addition to the main low sound of laryngotracheal respiration. The change the timber of the main sound.

Bell bronchial sound is loud, high-pitched, ringing like metal. This is characteristic for open pneumothorax (pneumothorax in which the pleural cavity communicates with the outer air and the air pressure in it is high).

It is necessary to remember that the conditions of good resonance responsible for amphoric and bell sounds can appear due to proximity of large smooth-walled air-containing cavities, therefore mistakes are possible.

Mixed respiration. Mixed or bronchial respiration is that in which the phase of inspiration is vesicular and that of expiration is bronchial. In healthy subjects it is heard over the right apex. In pathological conditions it can appear if dense areas of the lung producing bronchial respiration alternate with the areas of normal pulmonary tissue producing vesicular respiration. This is observed in bronchopneumonia, pulmonary tuberculosis, pneumosclerosis.

Materials for self-control (added)

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