The close study of the healthy chest sounds upon the living animal is an
essential prerequisite to the appreciation of the morbid. The abnormal
noises are so varied, merge into each other by such imperceptible
degrees, and so coexist and complicate each other that they often prove
extremely puzzling to the unpractised ear. It is no more necessary that
the musician should educate his ear to appreciate the most delicate
gradations of musical notes, than that the auscultator should educate
his in the sounds of the healthy and diseased chest. Written
instructions are of about equal value in the two cases, they prove
auxiliaries in the acquisition of knowledge but they can never supersede
the practical study of the chest. A mere theoretical knowledge is too
often useless in the presence of the patient.
The abnormal chest sounds are either modifications of those existing in
health, or superadded sounds which have no counterpart in the healthy
chest.
_Modifications of healthy sounds._ The =vesicular= or =respiratory
murmur= may be =increased= or =diminished= in force or it may be
entirely =absent=.
=Increase of the respiratory murmur=, is merely an increase in force
without any modification in character and resembles _juvenile_
respiration. If increased equally over the entire chest it is =general=,
if only in a part it is =partial=. =General increase of the vesicular
murmur= is heard after an animal has been submitted to moderate exertion
for ten or fifteen minutes. In animals at rest it is heard in active
fevers and in the symptomatic fever which attends acute inflammations.
=Partial increase= as for example in one lung only, or in circumscribed
parts of both lungs, and especially along their superior borders, is
indicative of disease of the lungs or the pleuræ. It testifies to the
impermeability to air of some other portion of lung, from congestion,
splenisation, hepatisation, plugging of a bronchial tube with tenacious
mucous, tubercular deposits, tumors, emphysema, or hydrothorax. (See
under these names.) The healthy portion of lung in such cases takes on
the function of the whole, and the loud breathing is called
=supplementary=.
=Diminution of the respiratory murmur=, like its =increase=, may be
=partial= or =general=. =General diminution= is seen in anæmia, in low
fevers, in all very prostrate conditions from the mere want of power to
dilate the chest; in general emphysema (broken wind, heaves), in general
miliary tubercular deposit in the lungs, or in that form in cattle in
which the tubercle has been replaced by cretaceous deposits, from the
animal’s inability to fully dilate the air cells; in enteritis,
peritonitis and metritis the chest is more fully dilated because of the
pain attendant on that act, and the breathing being short and quick the
murmur is correspondingly low. In certain brain diseases with sluggish
respiration the sound is equally feeble.
=Partial diminution of murmur= is more surely indicative of lung
disease. It may arise from partial congestion when a supplementary
murmur will be observable over other parts of the lungs, and a crepitant
râle soon appears in the congested part; from local emphysema in which
there is increased resonance in percussing the part; from tubercular or
cretaceous deposit, when there will be exaggerated murmur elsewhere, or
from bronchitis with blocking up of one or more small bronchial tubes
and with louder respiratory sound in other parts.
=Absence of respiratory murmur= may be due to various causes, all of a
diseased nature. Hepatisation of lung may be recognized when this
condition is found associated with a crepitating râle around the margin
of the silent part, and when percussion shows its solidity and want of
resonance. Splenisation is associated with absence of respiratory sound
and dullness on percussion, but no surrounding crepitation. Absence of
sound in water in the chest is confined to the lower part of the chest,
keeps the same level and ratio of increase in front and behind, and in
the horse on the two sides, and has been preceded by the characteristic
catching breathing and the friction sounds of pleurisy. Large tumors and
extensive and circumscribed tubercular deposit will give rise to absence
of sound over a limited area and plugging up of one or more bronchial
tubes will lead to a similar result. Hepatisation of lung and water in
the chest are, however, the common causes of loss of respiratory murmur.
The =bronchial or tubal sound= may be increased in pitch and in
harshness in two conditions. 1st. In the early stages of bronchitis when
the lining mucous membrane of the air passages is dry, thickened and
inelastic. 2d. When that portion of lung intervening between one of the
larger tubes and the surface of the chest is solid (hepatised) and thus
proves a better conductor of sound than in the normal condition.
=Superadded abnormal sounds.= The =bronchial= sounds may be altered in
their character so as to become =cavernous=, =amphoric= or =mucous=
(rattling). The =cavernous= sound is usually caused by the presence in
the lung of the cavity left after the discharge of an abscess or
softened tubercle into a bronchial tube. It is thus preceded by cough
and white, creamy discharge from the nose. If the discharge is fetid and
grumous there has probably been circumscribed gangrene of the lung. An
approximation to the sound may be produced by blowing into a widemouthed
glass or porcelain vessel. The sound of =amphoric respiration= on the
contrary is like that made by blowing into a narrow necked bottle. It is
due to a similar cavity with a small orifice or to the existence of
pneumothorax communicating by a narrow canal with a bronchial tube. It
is rare in the lower animals, but Delafond mentions one case in the
horse and two in dogs.
=Râles.= The remaining morbid sounds are known as _râles_, or rattles.
They may either be referable to the bronchial tubes or the lung tissue.
They are called dry or humid, according as they convey the idea of air
drawn through a dry tube or one containing liquid.
The =dry râles= are due to narrowing of the bronchial tubes from the
pressure of adjacent tumors, the thickening of the mucous membrane or
the deposition on the surface of layers of tenacious mucus. The greater
the narrowing the shriller the sound, and hence the distinction of
_bronchial râles_ into =sonorous= and =sibilant= (whistling).
The =sonorous râle= has been variously exemplified by the humming of a
gnat, the cooing of a wood pigeon or the bass notes of a violin. It
commonly bespeaks the onset of bronchitis and testifies to the
thickened, dry and rigid character of the tubes, but may give place in
as short a time as three hours to a mucous râle from the occurrence of a
free secretion. It rarely extends over two or three days. Sometimes when
caused by a piece of tenacious mucus obstructing a tube, it is very
transient disappearing at once when the mucus is expelled by coughing.
Sometimes it is modified by an occasional clicking sound from the
flapping of a shred of semi-solid mucus attached to the walls of a
bronchial tube. This disappears when breathing becomes more hurried.
The =sibilant= (whistling) =râle= often acknowledges the same causes as
the sonorous, but indicates a narrower closure of the tubes. More
frequently it is heard further back on the chest and results from
pulmonary emphysema and dilatation of the smaller bronchial tubes
(broken wind, heaves). It is then heard chiefly in expiration and
coincidently with the second quick lifting of the flank. It is further
associated with the double lifting of the flank in expiration with the
short, weak, paroxysmal cough and the indigestion characteristic of
broken wind. If the whistling noise is so loud as to be heard without
applying the ear to the chest it is called wheezing.
A =mucous râle= is caused by air passing through any liquid contained in
the bronchial tubes, such as mucus, pus, or blood. It may be imitated by
blowing a large number of soap bubbles in a thick lather and noticing
them burst simultaneously or successively. It is chiefly observed in
bronchitis after the preliminary dry stage of the mucous membrane has
passed off and an abundance of mucus has been secreted. The nature of
the sound will vary according as it comes from the larger or the smaller
tubes or in other words as to whether the bubbles are large or small.
That from the smaller tubes is sometimes called a =submucous râle=.
Either of these râles may be temporary or permanent as the mucus may be
momentarily cleared away by coughing.
The =crepitant râle= is a sound of very fine crackling which has been
variously compared to the crackling of salt when put on red hot coals,
the noise of a sponge expanding in water and the rubbing of a small lock
of hair between the finger and thumb close to the ear. The existence of
the _crepitant râle_ usually denotes the existence of the early stage of
inflammation of the lungs, and the progress of hepatization in such
cases may be traced by the advance of the line of crepitation which
precedes it. So the progressive absorption of exuded matter in recover
may be equally followed by a line of crepitation gradually decreasing in
area until it meets in a point. The observations will be corroborated by
the dull sound elicited on percussing the parts. The production of the
sound has been attributed to the passage of air through the thick mucus
in the smallest bronchial tubes or more plausibly to the separation of
the walls of the air sacs and cells during inspiration, they having been
previously adherent by reason of the secretions.
_Crepitation_ is not heard in all pulmonary inflammations. In weak
animals with a low type of inflammation tending to gangrene, and in
those cases of broncho-pneumonia in which a viscid mucus blocks up the
bronchial tubes passing to the affected lobes, it may be altogether
absent.
_Crepitation_ may further occur without inflammation. Thus in pulmonary
œdema (dropsy of the lung) and capillary hemorrhage in which liquids are
effused in the smaller bronchial tubes and air sacs a crepitation is
sometimes heard.
A =modified crepitation= (=dry crepitant râle= of Delafond) is usually
heard over an emphysematous lung. The noise in this case has been
compared to that induced by handling a sheet of paper.
The =subcrepitant râle= is another modification holding a place
intermediate between the crepitant and the mucous râles. It has been
likened to the sound of a moderate effervescence in beer or other
liquid. It is referable to the presence of mucus in the smaller
bronchial tubes and indicates bronchitis or broncho-pneumonia.
Still other sounds are heard in diseased conditions of the pleuræ. These
are =friction sound=, =creaking=, =metallic tinkling=, and =gurgling= or
=splashing=.
A =friction sound= is heard in the early stages of pleurisy and is
caused by the dryness of the pleural surfaces from the absence of the
halitus or vapor which normally moistens them and the deposition of
layers of lymph by which the surfaces are rendered rough and uneven. An
approximate sound may be observed by placing the palm of the left hand
on the right ear and drawing a finger of the right softly over its back.
The sound is quick and jerking, one or a few jerks only being heard with
each inspiration as the act is cut short on account of the pain
attending the friction. It is rarely heard in expiration. It is chiefly
heard at the lowest part of the chest where the lungs have the greatest
freedom of movement. The thinness of the walls of the chest above the
breast bone in cattle and dogs permits the friction sound to be heard
more distinctly than in the horse. After the lapse of twelve,
twenty-four or forty-eight hours the friction sound disappears, the
surfaces of the pleuræ being separated by the liquid effusion, but it
may reappear when the fluid is absorbed in the process of recovery.
Sometimes the friction is further manifested by vibration of the walls
of the chest perceptible to the touch.
The =creaking sound=, as from the bending of a piece of strong leather
is caused by the movement of a thick and solid false membrane binding
the lungs to the side of the chest. This is often confounded with
crepitation.
=Metallic tinkling= is only heard when liquid and gas both exist in the
pleural sac and is due to the falling of a drop from the shreds of false
membrane above into the fluid contents below. The sound is somewhat like
the falling of drops in a closed cask half full of water, or it may be
fairly exemplified by placing the palm of the left hand flat on the
right ear and striking the back of the hand smartly with the middle
finger of the right. The sound is chiefly heard after the patient has
changed its position and especially after rising. The explanation of
this is that in the recumbent position the liquid changes its place and
bathes parts which in standing are surrounded by gaseous products only.
Drops accordingly fall into the liquid for some time with diminishing
rapidity until they cease altogether. Other explanations of the sound
but which less frequently exist are: the ascent of a bubble through the
liquid and its bursting on the surface; and the sudden recoil of air
from one wall of the plueral cavity to the other as the result of
movement or sound generated in the deeper seated solid structures.
A =gurgling= or =splashing= sound is equally indicative of the presence
of fluid and gas in the pleural sac. It is almost never heard unless
after a sudden movement on the part of the patient causing considerable
commotion in the contained liquid. Gurgling sounds transmitted from the
abdomen are too often mistaken for this. In small animals with
hydro-pneumothorax a quick shaking of the patient will develop it.
=Auscultation of the Cough= is sometimes valuable, though more difficult
and less satisfactory in the lower animals than in man, chiefly because
of the extensive movement of the ribs in the former. As conveyed through
a healthy lung to the ear applied on the side of the chest, the sound is
short, dull and indistinct. When the lung is more solid from
hepatisation, pleural exudation or other cause, or when the bronchi are
dilated the sound is loud and strong. The extent over which it may be
heard thus forcibly agrees with the area of lung in a state of
consolidation. When a considerable cavity or canal communicates with a
bronchial tube and extends to near the surface of the lung the sound is
loud and ringing. The note is specially clear and metallic when such a
cavity opens into the bronchus by a narrow orifice; an apt illustration
of this noise may be obtained by coughing into a narrow necked vessel.
The results obtained by auscultation should be confirmed by percussion
before arriving at any definite conclusion as to the state of the chest.
Consolidated lung tissue is a much better conductor of sound than the
healthy, and sounds conveyed through this may be heard at a considerable
distance from their point of origin. Thus the heart sounds are
frequently heard over any part of the right side of the chest, and
crepitation and other sounds may be heard in the centre of a hepatized
portion. On all such occasions the dull sound elicited on percussion
will not fail to correct the fallacy.