again a distinct "break" occurs in passing from a very light to a fairly The Vesicular Element. In addition to the laryngeal sound just described, a vesicular element is added which, when auscultation is practised over the chest, furnishes most of the inspiratory pulmonary breath sound. It is due to the separation and distention of the alveoli by the inrushing current of air. The expiratory portion appears to arise in the upper respiratory tract. The fact that the sound heard over the chest wall is more muffled, weaker and lower in pitch than that audible experimentally over the actual periphery of the lung is due to loss of vibratory intensity in passing from the lung to the chest wall and from the chest wall to the stethoscope (vibratory reflection). The Basis for the Assumption of Alveolar Sound Production. The cubic capacity of an alveolus is 0.00494 mm. (Zuntz). In long-necked animals, such as the ruminants, the respiratory murmur is much less loud than in the short-necked ones, such as the carnivora. The estimated total of the alveoli is 400 million. As the average lung volume is 4000 cm., 1 cm. would include 100,000 alveoli. If we assume that in ausculting we hear sound from a depth of 3 cm., we would perceive sound yielded by half a sphere 14 em. in circumference. In other words, we would hear the combined sound of 1,400,000 alveoli. Since a normal deep inspiration takes 2 seconds, we should hear the sound of 700,000 alveoli per second. Now we cannot recognize as separate sounds, vibrations occurring with a rapidity of 700 per second, as would be the case if 1000 alveoli gave forth sound simultaneously. But alveolar distention is gradual and when a sufficient number of sequent groups produce sound, it is extremely plausible to assume that an audible sound is thus engendered. Only on such a hypothesis can we assume that sound is produced in the alveoli. The dimensions of an alveolus are so small that there is no possibility of sound production after the manner in which it occurs in the trachea or bronchi. "There can be no question of inspiratory vibration, reflexion, interference, or the formation of horizontal waves where there is no reflective wall because the relationship between the size of the waves and the chambers is too disproportionate" (Geigel, p. 172). "The total alveolar surface of the lung amounts to no less than 90 square meters, or 100 times the body surface."1 The interlobar bronchioles end in narrow alveolar ducts and these "expand in turn into comparatively wide infundibuli lined by air cells. This sudden widening out of the air passage is believed to aid in the production of the inspiratory sound heard in ausculting the lungs, eddies being set up in the passage of the air from the narrower to the wider cavity" (Hutchison). Sahli found in a case of pulmonary hernia due to a sternal fissure that characteristic vesicular breathing could be heard over the hernia during the performance of the Valsalva experiment, in which of course all laryngeal and glottic sounds were eliminated, and proving that at least a part of the vesicular sound originated in the vesicles themselves. The vesicular sound is also noted in cases of cardio-pulmonary murmurs, a factor which further corroborates the foregoing statement (Sahli, Correspondenzblatt f. Schweizer Aertze, 1892). 1 R. HUTCHISON: "Applied Physiology," 1908. The greater part of the expiratory sound is produced by the passage of air over the vocal cords and through the glottis. It contains, as well, certain sounds arising in the oral and nasal cavities and some contributed by the trachea and the bronchi. The greater part of the inspiratory portion arises in the vesicles. In as much, therefore, as both, but especially the expiratory portion, have a composite genesis it is not surprising to find that the breath sounds heard over the chest may vary in different individuals, and even in the same person under varying conditions, in regard to intensity, quality, duration and pitch. CHAPTER IX NORMAL AND ABNORMAL BREATH SOUNDS THE NORMAL VESICULAR SOUND The sound normally heard over pulmonary tissue during the act of breathing the vesicular murmur-is regular in rhythm, low in pitch, and soft, breezy or rustling in character. It is heard throughout respiration, but progressively diminishes in intensity during expiration, the end of which is inaudible. There is only a very brief pause between in- and expiration. It is to be noted that although the duration of these two physiologic phases of respiration is as 5 to 6, the audible duration is as 5 to 1, respectively. In other words the expiratory sound is much shorter than that of inspiration, and sometimes it is barely audible. Being a purely passive act, which results from the elastic recoil of the distended lung tissue, it is less harsh, and lower in pitch, as well as shorter than inspiration. The elastic recoil is greatest at the end of inspiration, hence the beginning of expiration is more intense than its end. Furthermore, the glottis is more widely opened during inspiration and the air leaves the chest less rapidly than it enters. The vesicular sound may be imitated by breathing deeply with the lips set in the position which produces a soft "F." In ausculting the lungs, the beginner especially, should note the character of the expiration, for it is in this phase particularly that pathologic abnormalities are most apt to occur. ABNORMAL BREATH SOUNDS The vesicular murmur may become abnormal owing: (1) to a change in its character (intensity, quality, duration, pitch or rhythm); or (2) to the introduction of new or adventitious sounds, i.e., (a) râles; (b) frictions; (c) succussion splash; (d) metallic tinkle. THE CLASSIFICATION OF ABNORMAL BREATH SOUNDS Abnormal breath sounds are more or less arbitrarily classified as (1) exaggerated, (2) broncho-vesicular, (3) bronchial, (4) cavernous, and (5) amphoric. Changes in the Intensity and Quality of the Breath Sounds.-Exaggerated Breathing. (a) A mere increase in the intensity of the respiratory murmur is known as exaggerated breath sounds, and is due to increased vesicular activity-more air entering in a given unit of time than is normally the case. Such a condition is normal in children, hence the name puerile breathing. It may occur in any individual who is breathing hard, as for instance after physical exertion. In women the respiratory sounds are louder than in men, especially in the upper, anterior thoracic region, and during expiration (costal breathing). In exaggerated breathing both in- and expiration are harsh and prolonged because the glottic sounds are louder and on account of the increased pulmonary tension (vicarious "emphysema"). (b) Decreased breath sounds (feeble, senile, emphysematous, breath. sounds) are characterized by the fact that the sounds are faint or short; expiration may be inaudible. This may be due to: (1) diminished sound conduction-bronchial obstruction (increased diffusion and reflection)pleural effusion or thickening (increased reflection) cutaneous adiposity or edema, etc.; or to (2) diminished sound production-shallow breathing arising from pain, muscular weakness, thoracic rigidity, pulmonary emphysema. FIG. 97. Diagram to illustrate the occurrence and non-occurrence of bronchial breathing in pneumonia. On the right side the consolidation spreading inward has reached the bronchus and as a result bronchophony and bronchial breathing are heard. On the left side there is still a break in the continuity of consolidation between the periphery and the large tubes, and although dulness is marked, bronchial breathing and This partial or entire bronchophony are absent. The breath sounds are feeble or absent. suppression of the breath sounds, especially of the vesicular element, associated with percussion dulness, and occasional rales on deep breathing, occurs in the early days of a pneumonia much more frequently than bronchial breathing. In the early stages of pneumonia and of pulmonary tuberculosis the sounds are often indistinct and muffled. (c) Breath sounds may be absent in pleural effusion, closed pneumothoraces with atalectasis, or from occlusion of a bronchus-pressure or exudation. "Diffusion of sound between the lung surface, free from adhesions, and the chest wall, shares the honors with reflection of sound from the fluid back into the air in the lung, in reducing the intensity of sounds in their passage from lung to chest wall in ordinary cases of pleural effusion" (Montgomery). Pleural effusions sometimes yield normal or actually increased fremitus, voice and breath sounds even below the level of the fluid. This phenomenon is ascribed by Montgomery to the fact that the lung is solid either as the result of exudation, infiltration or compression and being such imparts its vibrations readily to the surrounding fluid without much of a "break" due to reflection. This state of affairs is only inadequately offset by the loss of sound through diffusion in the effusion, so that the end result is at least "normal" if not actually an increased intensity of transmission. A similar effect although less in degree may be exerted upon fluid by a collapsed lung. It is furthermore evident that anything which tends to bring the lung near to the chest wall-adhesions, large lungs and small thoraces (in infants)-would further tend to prevent the disappearance of fremitus, resonance and breath sounds, in cases of pleural effusion. Broncho-vesicular Breathing.-This is a combination of the vesicular and the bronchial types, both the soft vesicular and the harsh bronchial elements being present, either one of which may predominate. Some authorities prefer to use the term vesiculo-bronchial if the vesicular sound is preponderant, and broncho-vesicular when the bronchial sound is the greater. Others prefer to include both these types under one heading, and modify the term by adding such adjectives as slight, marked, harsh, intense, etc. Physiologic broncho-vesicular breathing is heard over definite locations at which it is normal and can be explained on anatomic grounds. considerably influenced by opening, narrowing or closing the mouth or the glottis; and tends to become more intense as a main bronchus is approached. The pathologic type of broncho-vesicular breathing may occur over any portion of the lung and is relatively uninfluenced by alterations in the oral resonator (breathing through the mouth or nose). It occurs when both normal vesicles and infiltrated pulmonary tissue exist together, as in incomplete consolidation. Bronchial Breathing. By this term which is synonymous with tubular breathing, we understand a loud, harsh, high-pitched, snorting type of breath sound, with a distinct pause between inspiration and expiration, the latter being even longer, more harsh and higher-pitched than the former. The soft, low-pitched, rustling or breezy vesicular element is entirely absent. The breath-sounds normally heard over the trachea are often used as an example of bronchial breathing, but the tracheal sound is generally more harsh and lower in pitch than that which occurs pathologically over consolidated lung tissue. As in normal breathing, the primary sound originates in the upper respiratory tract. Bronchial breathing is characteristic of consolidated lung because conditions are less unfavorable for sound transmission than is the case in normal lungs. The vibrations pass from the bronchial wall to the surrounding consolidated lung and thence to the chest wall without undergoing a serious "break" in the process of transmission. This is so because bronchus, solid lung and chest wall are acoustically more or less identical and there is, therefore, not much chance for diffusion or reflection of the vibrations at the different tissue junctions. Montgomery has shown that lung under normal tension transmits sound much less well than either relaxed or consolidated pulmonary tissue. "The occurrence of weaker sounds over the normal chest than over the |
