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by the fact that some part of the rubber tubing comes into contact with the garments, etc.; (c) sounds produced by the interposition of garments between the ear and the chest. Needless to say it is useless to attempt to auscult through stiff materials such as starched linen. (d) Contracting muscle produces a sound, hence any muscular tremor or voluntary stiffening of muscles on the part of the patient must be prevented. The examining room must not be cool enough to produce shivering. Muscle sounds are especially common over the pectoralis major in the anterior axillary region and over the trapezius muscle. (e) Occasionally the physician may, when the stethoscope has been placed in the auditory meatus, become subjectively conscious of his own circulatory sounds.

In ausculting the chest, sounds are frequently heard which to the beginner, sound like râles. If the patient swallows while one is listening over the chest the sound produced resembles very clearly that produced by a râle. This is especially apt to occur when the patient coughs and then takes a moderately deep breath. As this procedure is employed especially to elicit latent râles, the patient should be cautioned not to swallow.

Occasionally when ausculting the axillary regions fine râles are heard during the first moderately deep inspiration. They are of no significance unless they persist during succeeding inspiratory acts.

At this place mention might be made of the transmission of sounds from the diseased to the healthy side. Very often the sound produced by large bubbling or resonating râles as well as exaggerated voice sounds and loud cavernous or bronchial breathing on one side may be heard on the opposite side. When this occurs it is always over the upper and posterior portion of the chest near the large bronchi. Mistakes may be avoided by noting the character of the percussion note and the breathing, and especially by tracing the sounds from their point of maximum intensity across to the opposite side. If the sounds are not due to bilateral lesions they will gradually diminish in intensity.

THE INFLUENCE OF POSTURE ON THE PHYSICAL SIGNS

The posture of the patient has certain definite modifying influences. upon the results of the physical examination. A sitting position is always preferable. If the patient lies upon the side, percussion of the lower lung yields a slightly impaired note with a tympanitic quality. The former results from the lessened amount of air which the lung contains, the latter from diminution of pulmonary tension and from the resonating property of the mattress. The resonating property of extraneous objects must be borne in mind. For example, pulmonary resonance is greater if the patient is percussed immediately in front of a door (sounding board) then if he stand in the middle of the room. Slight dulness over one pulmonary apex which may be readily demonstrable when the patient sits up, may disappear if percussion is performed in recumbency while the thorax rests upon pillows or a soft mattress (resonators).

In the lateral decubitus the breath sounds in the lowermost lung tend to become muffled and feeble, owing to the decrease of tidal air. In the uppermost lung, on the contrary their intensity may be increased.

THE STETHOSCOPE

The main functions of the binaural stethoscope are (1) to prevent lateral radiation of vibrations with which the air it contains, is charged, thus conducting a larger proportion to the ear, and (2) to exclude extraneous sounds. A large bell furnishes more sound than a small one, because it covers a larger area of vibration-emitting surface. The bell may also act as a resonator and reinforce certain vibrations. Thus a bell 2 inches in diameter enables us to judge accurately regarding intensity and rhythm, but is inferior to a bell of ordinary size or to the unaided ear in the judging of equality and pitch (Flint). Furthermore it is evident that depending upon its shape and the elasticity of the material of which it is made, the resonating quality of the bell must vary considerably. A small bell is also advantageous since it enables us to localize sound more sharply, this being especially important in ausculting the heart and the supraclavicular apices, as well as in children and emaciated individuals in whom the projecting ribs interfere with close application of the bell.

The importance of the thoracic wall in acting as a resonator of the laryngeal vibrations has already been alluded to under vocal fremitus (p. 47). The sounds that we hear are due to both visceral and mural vibrations. The latter sometimes preponderate in intensity and having a lower pitch have a greater volume; whereas the higher range due to the fundamental note is often medically of greater importance. Mural vibrations can to a certain extent be eliminated, and the visceral vibrations studied in isolation by exerting marked pressure, with the bell of a a binaural stethoscope equipped with rubber tubing.

In case of the mon-aural stethoscope made with a hollow or solid stem of metal, vulcanite or wood, transmission occurs both through the stem and through its contained air. The thinner the walls of the stem and the bell, the more easily will sympathetic vibrations be set up and transmitted to the ear. A large part of the sound is thus transmitted by the solid stem. This applies to a slight extent also to the modern binaural stethoscope, in which some sound is conducted by the rubber tubing, which tends to reinforce the aerial vibrations. Nor "is it immaterial what thickness of tubing we employ. It must be neither too flexible nor too rigid. High-pitched sounds are conducted along tubes, especially soft tubes much less readily than low-pitched sounds, because of their smaller mass."

In using the binaural stethoscope with rubber tubing, the results of pressure on the thoracic wall are quite different. In case, for instance, that the bell is thick-walled, and possessed of a high fundamental note it will be much less affected by the damped mural vibrations than is the case with the monaural stethoscope.

"A solid body laid upon the chest wall takes up and transmits according to its own elastic properties the vibrations emanating from the latter. When the pressure of the solid body upon the surface is sufficiently increased, the sensible vibrations of the latter are damped, but their energy is, of course, transferred to the body which extinguished them. When, for example, the mon-aural, solid stethoscope is applied to the chest, the sounds heard through it are not deadened by increasing the pressure of contact; on the contrary, they tend to become more intense, and are brought

nearer the ear." The diaphragmatic type of instrument yields louder sounds than a simple bell, because it covers a large area of sound emitting surface and because the diaphragm prevents the encroachment of the soft tissues upon the lumen of the receiver (Montgomery). Perhaps also the sound waves are amplified by the vibrations of the disc. At all events, this type of instrument should be used as a magnifying lens to study detail and, especially by the beginner, not as the sole method of auscultation. The sounds heard are not merely intensified, often they are distorted because the instrument disproportionately magnifies certain sounds.

"Binaural stethoscopes and to a minor degree phonendoscopes are less well adapted for the auscultation of faint, high-pitched murmurs, wheezy sounds and the metallic phenomena."

Pulmonary sounds are often heard better with the unaided ear, applied directly to the chest wall, because in such cases we get bone conduction as well as ear conduction. The early stages of pulmonary consolidation, the tubular quality of bronchial breathing, and at times the diastolic aortic murmur are also better appreciated without a stethoscope.

On the other hand, the vesicular element of the respiratory murmur, heart sounds and generally speaking murmurs, also certain râles are more easily analyzed with a stethoscope. This is perhaps due to the fact that certain wave lengths bear a definite reinforcing relation to the size of the receiver and the length of the stethoscope tubing.2

With a small bell we can localize more sharply but we get less volume. Therefore, wider bells give better results for feeble sounds-weak murmurs, fetal heart sounds, etc. For the latter deep pressure on the abdomen is also requisite.

If a stethoscope with a spring is used, the curvature of the metal parts and ear pieces should correspond to that of the external auditory meatus, since the opening in the ear piece should point directly toward the drum and not toward the cartilaginous meatus. Owing to differences in the angle of individual ears, stethoscopes with metal ear pieces must have adjustable angulations. It is partly for this reason that the author prefers simple rubber tubing without any spring attachment whatever.

The Choice of a Stethoscope. This is largely a question of personal preference. A small minority still prefer the mon-aural type, perhaps as a matter of habit. Certainly two ears are better than one, especially when one is hampered by extraneous noises. In a choice between many binaural types certain factors must be considered:

1. The ear pieces must fit the external auditory meatus exactly, not only in order to exclude outside noises, but also so that the instrument can be used indefinitely without discomfort or pain. A little time consumed in filing the ear pieces to the proper shape and dimensions is well spent.

2. Instruments of the phonendoscope type-those with diaphragms -should never be used by beginners. They not only magnify, but also distort, sounds. Their habitual use even by more experienced clinicians establishes a false standard of normality, and often renders the examiner more or less helpless in case they are temporarily unavailable.

1 SEWALL, HENRY: "The Rôle of the Stethoscope in Physical Diagnosis." Amer. Jour. Med. Sci., February, 1913, p. 234.

2 CONNER: N Y. Med. Jour., July 13, 1907.

3. The tubing should not be smaller than the caliber of the metal parts, and should be sufficiently heavy to prevent kinking.

4. An extra bell (receiver) smaller than the usual size is desirable, especially in the practice of pediatrics.

5. The instrument should be light and compact so that it can be readily carried in the pocket.

The author personally prefers the Sansom instrument with two bells, and furnished with an extra diaphragmatic receiver for occasional use.

THE BREATH SOUNDS

The act of breathing causes certain sounds which are known as the breath sounds or the respiratory murmur. The breath sounds may be heard when the ear is applied to an area of the thorax overlying lung tissue. They are composed of: (1) the laryngeal or "bronchial," and (2) the vesicular elements.

The Laryngeal Element. During both inspiration and expiration certain sounds are produced in the nose, mouth, glottis, larynx and trachea. They are due to sonorous vibrations caused by a column of air moving through the structures in question (Fig. 96).

If we listen over the trachea during the act of respiration we generally hear high-pitched sounds, having a tubular quality, with expiration lasting as long or longer than inspiration; the former having a higher pitch than the latter and being separated from it by a distinct interval. When we listen over the lung these sounds have undergone a great modification. The sounds are softer, lower in pitch, expiration is very short, and faint, indeed often it is inaudible, while the pause separating inspiration has practically disappeared.

Stenosis of any portion of the upper respiratory tract, such as by nasal or faucial adenoids, markedly increases the intensity of the laryngeal element of the respiratory murmur. Such obstruction may cause broncho-vesicular breathing over the pulmonary apices, thus simulating infiltration of the lung. It is to be distinguished from the latter by its bilateral character, disappearance when the obstruction is removed and by the absence of percussion dulness (Fig. 95).

The primary sound producing vibration in the respiratory system arises in the vibrations of tissues, not of the air. The moving air sets the tissues in motion; this produces a sound, which is in turn conveyed or conducted by the air, as well as by the tissues which surround themthe bronchi and pulmonary tissue.

The relationship is that of the bow, to the violin string, the former being represented by the air current, the latter by the tissues. Furthermore, the rapidity of the current affects the intensity of the sounds (amplitude of the vibrations). When the air current is rapid, more intense breath sounds are produced. Just as the voice sounds produced in the larynx are carried downward into and through the pulmonary tissues, so are the breath sounds, which arise at the same source.

"The chief effect of the bronchial walls is to prevent diffusion, thus allowing the good conducting properties of the air to operate at advantage.'

The voice and breath sounds lose much of their intensity as we hear them over the chest wall, (1) as a result of diffusion, although this loss

is more or less offset by the deep penetration of the bronchi into the pulmonary tissue; (2) owing to reflection which occurs when the airborne vibrations pass through the walls of the bronchi; (3) because in

[graphic][subsumed][subsumed]

FIG. 96.-This antero-posterior section through the head and thorax depicts the structures concerned in the production and modification of the "laryngeal" element of the breath sounds.

Auscultation over the area "A" during nasal breathing, the mouth being closed, yields pure cavernous breathing (low-pitched sounds with a hollow or reverberating quality, and expiration longer than inspiration). The outgoing air strikes the nares more directly than when the mouth is open; the vocal cords are more closely approximated during expiration and vibrate considerably. The nares and the mouth furnish the cavity for the reverberation of sound, and the occipital bone is a good conductor.

Auscultation over the area "B." If the mouth is open, the air passes directly out of it, the nasal resonator has been eliminated and the cavernous quality as well as the intensity of the breath sounds almost entirely disappear. The results of tracheal auscultation are also greatly modified by oral and nasal breathing. (Barach.)

passing from the bronchial walls into the pulmonary septa more wave energy is lost by reflection; (4) as similar loss occurs in passing through the air chambers of a normally distended lung; (5) since they meet with reflection again in passing from the lung to the chest wall, because here

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