Iowa State University Veterinarian

Volume 25 | Issue 2 Article 2

1962

General Auscultation of Large AnimalsGeorge W. AllenIowa State University

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Recommended CitationAllen, George W. (1962) "General Auscultation of Large Animals," Iowa State University Veterinarian: Vol. 25: Iss. 2, Article 2.Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol25/iss2/2

General Auscultationof

Large Anilllais

George W. Allen, D.V.M. (V.S.)

A uscultation is defined as the act oflistel~ing for sounds within the body

( 11 ). It is used chiefly to detect soundsconnected with the lungs, heart, pleura,and areas of the abdomen. Until recentyears, immediate auscultation, that is plac­ing the ear directly on the part, was thecommon means of detecting sounds. To­day a stethoscope is usually employed inroutine auscultation examinations.

Although Laennec is usually creditedwith the original use of auscultation, Rob­ert Hooke (1635-1 703) nearly a centuryand a half earlier included in his writil~gs

the following: "There may also be a possi­bility of discovering the interl~al motionsand actions of bodies-whether animal,vegetable, or mineral, by the sound theymake; that one may discover the worksperformed in the several offices and shopsof a man's body, and thereby discoverwhat instrument or engine is out of or­der-in plants one might discover by thenoise of pumps for raising the juice, thevalves for stopping it-methinks I canhardly forbear to blush when I considerthe most part of mel~ will look upon this­I have been able to hear plainly the beat­ing of a man's heart-to their becomingsensible they require-that the organ bemade more nice and powerful to sensateal~d distinguish them." (43).

~:~ Dr. Allen is an instructoT in th'e Departmentof Medicine and Surgery at the Iowa StateUniversity Veterin'ary Clinic.

Issue, No.2, 1962-63

In order to use auscultation to its great­est advantage an understanding of someof the basic phenomena of sound is essen­tial. Sound is mechanical wave motiol~ inan elastic medium. One complete sinusoi­dal wave fron~ crest to crest is termed acycle. The frequencies of audible soundwaves lie between about 20 cycles persecond (c./s.) al~d 20,000 c./s., whileaud:lble heart sounds range from about 50c./s. to 650 c./s. The production of soundwaves requires a mechanical disturbance( the source) and an elastic mediumthrough which the disturbance can betransmitted. Generally speaking the den­ser the transmission medium the betterthe transmission. Thus bronchial soundswill be heard better through consolidatedlung than through lung affected with gen­eralized emphysema.

The intensity of a sound is defined asthe power a soul~d wave transmits througha unit area normal to the direction ofpropagation. Intensity is related to loud­ness in that loudness is, generally speak­ing, a physiological assessment of inten­sity. It should be renlembered that inten­sity decreases by the square of the dis­tance, thus a small change in the distanceof the stethescope head from the soundsource will greatly affect the intensity.A musical sound is composed of a com­plex group of sound waves with somesemblance of regularity; a noise has noselnblance .of regularity and consists of a

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series of random displacements. Soundsheard in routine auscultation are usuallynoises.

Careful auscultation of the heart is es­sential for a thorough physical examina­tion. The first sound is heard best overthe cardiac apex while the second soundis more audible over the base of the heart.Closure of the tricuspid valves is best dis­cerned over the right precardium, closureof the mitral, over the left precardium.The semilunar closure is heard more pos­terior on the left precardium thall is thepulmonary closure. From a practical pointof view, however, it is necessary to movethe stethescope to three or four positiollSover the area of the heart in order to de­termine if abnormal sounds are present asmany of them are very localized. Whileauscultating the heart, intensity) rate,rhythm, and quality of the sounds shouldbe noted as well as careful observation asto whether or not abnormal sounds arepresent. Interpretation of the heart soundsis performed by keeping in n1ind the ven­tricular volume curve. (Figure 1). Theintensity of the first heart sound is influ­enced by many factors, an10ng whichare: (a) the position of the valves at theonset of ventricular systole, which is us­ually detern1ined by the length of tin1eelapsing between atrial and ventricular

2nd heart sound

1st heart sound

.Presystolic gallop

Figure 1. Ventricular Volume Curve.

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coniraction, (b) the rate of rise of ven­tricular pressure and (c) the presence orabsence of structural disease of the mitralvalve. Aside from such factors as obesity,emphysema, and effusions of the chest,all of which affect the intensity of boththe first an,d second sounds, the intensityof the second sound is usually related tothe pressures in the aorta and pulmonaryartery. Accentuation of the second soundis also a normal phenomenon with in­creasing age especially if lesions of ar­teriosclerosis are present.

Generally, the heart rate is an indica­tion of the metabolic rate of the animal.Toxemia, pain and various forms of an­oxia plus any condition which causessevere circulatory collapse are commoncauses of an increased cardiac rate. Car­diac rhythm, however, is an indication ofthe state of the impulse conduction mech­anism of the heart. In many cases ab­normalities in rhythnl require the use ofan electrocardiogram for positive diag­nosis on the basis of auscultation alone.

Sinus arrhythmia is observed com­monly in domestic animals. It is char­acterized by a quickelling of the heartduring inspiration and a slowing duringexpiration. It has no clinical significance.Auricular fibrillation is also fairly easy todiagnose on auscultation because it is theonly common condition which has a wellmarked tachycardia with gross irregularityof rhythm. Another disturbance of con­duction occasionally found is the so-calledheart block. This condition may occur inanyone of three major degrees. A first de­gree block is all electrocardiographic diag­nosis; a second degree block is character­ized by the dropping of the odd ventricularbeat. The third degree block is usuallycharacterized by a slow heart rate with thefirst sound varying in intensity; the historyshows periodic syncopy. Gallop rhythmsare usually serious ill other animals butare heard frequently in the adult bovineand usually have no clinical significancefor the latter.

The discernment of heart murmurs isoften important in making a diagnosisand especially important ill making an ac­curate prognosis. Once a murmur is heardit must be determined whether it is func-

Iowa State University Veterinarian

tional and of little significance or whetherit is structural and of major importance.For practical purposes, all diastolic mur­murs are functional in nature (19) andare rarely heard in large animal medicine.Systolic murmurs, on the other hand, aremuch more freque11t and are usually ofsome clinical significance. Auscultationof cardiac murmurs combined with carefulpalpation over the precardial area is oftenof value as a murmur will often be veryfaint on auscultation but a thrill will bepresent on palpation. The latter usuallyoccurs in those conditions of relativelylarge pathological abnormality.

In recent years phonocardiography hasbeen used in diagnostic medicine to dif­ferentiate various murmurs. The value ofphonocardiography in clinical work lies inits ability to record for objective analysisthe transient sounds a11d nlurmurs towhich the hearing mechanism of differentobservers adds or subtracts subjectivevaria11ts (14). Present day phonocardi­ography has developed mainly through im­proved instrumentation with low-noiselevel amplifiers and satisfactory filters.Usually an electrocardiogram, phonocardi­gram and a carotid pulse are all recordedtogether so that the sound recordings canbe significantly correlated with the activ­ities of the heart. Figure 2 is an exampleof such a recording; it shows a diamondshaped aortic murnlur typical of aorticstenosis.

Although phonocardiography is a valu­able teaching aid for tIle fine distinctionof various murmurs, careful auscultationby a clinician will, in most cases, result inan accurate diagnosis of the cardiac abnor­mality heard.

Differentiation of functional murmurs

~ ktL • '.. &\ -AO.A. • •• pq

Figure 2. Electrocardiogram, phonocardiogram,and carotid pulse. The phonocardiogram is fromthe aortic area. The diamond shaped aortic mur­mur and the shape of the carotid pulse indicateaortic stenosis (14).

Issue, No.2, 1962-63

from those caused by structural lesions isvery important though often difficult. Theso-called haemic murmur, a functionalmurmur found in animals suffering fromanemia, debilitation, toxemia, etc., is usu­ally very soft and waxes and wanes withrespirations. It is usually discernible onlyafter very careful auscultation. The nlur­mur caused by stenosis of the aortic sem­ilunar valves is characterized, however, bya harsh systolic murmur most audible overthe dorsal posterior area of the heart base.A diastolic murmur heard in the samearea and accompanied by a high pulsewave and the absence of a thrill is charac­teristic of aortic semilunar insufficiency.Stenosis and insufficiency of the pul­monary semilunar valves produce similarmurmurs only on the right side just pos­terior to the heart base and of course donot disturb the pulse. Stenosis of the leftatrioventricular valves is characterized bya diastolic murmur over the apex of theheart on the left side with the length ofthe murmur rather than the intensity asan indication of its severity. A systolicmurmur most audible in the same areais probably due to insufficiency of themitral valves with little to no change inthe pulse. Stenosis and insufficiency ofthe tricuspid valves of the right side givemurmurs similar to those due to mitralpathology. One exception is that theformer are more audible over the right sidethan over the left and usually has a morepronounced jugular pulse.

Systematic auscultation of the lung areaof the thoracic wall will often be ofdefinite aid in arriving at a diagnosis.Figure 3 shows such a systematic ap­proach where each number indicates anarea over which the stethoscope should beplaced.

Sounds heard in the lung are of num­erous types. Roughly, they may be brokendown as follows: bronchial tones, vesicularmurmurs, and rales - both dry and moist.Bronchial tones are produced as air movesin the bronchi somewhat in tIle samefashion as sounds are made in a closedorgan pipe. Rales on the other hand arebronchial tones plus the sounds producedas a result of material in the bronchi.Moist rales occur when excess fluids such

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36

4

terized by slight bronchitis and bronchio­litis with an eventual increased intensity ofbronchial sounds due to consolidation ofthe parenchyma of the lung. Generallyspeakil1g, bronchial and virus pneumoniaoccur initially in the anteroventral areasof the lung whereas parasitic lungwormpneunlonias are first evidenced in the dia­ph,ragmatic lobes.

Pleuritic friction sounds are usuallydry, of varying 11arsllness, and occur whentwo layers of dry inflammed pleura rubtogether. They are usually present inpneumonias although often for only ashort time during the course of the dis­ease. Pulmonary emphysema al1d oedemaare common diagnoses on auscultationof the thorax. In pulmonary oedema thereis a reduced vesicular sound due to thealveoli not being able to distend with air.Too, if the oedema is extensive and gen­eralized, the pulmonary sounds have amoist quality. Emphysema is character­ized by some loss of nurmal lung soundsdue to poor conduction plus evidence offaint crepitation.

Various peristaltic sounds are oftenheard during auscultation of the thorax.This is especially true in cattle wheresounds originating from swallowing, re­gurgitation, and reticular movements arequite pronounced. Care should be exer­cised, however, in differentiating thesesounds from those resulting from a dia­phragmatic hernia. The latter soundsusually have a tympanitic quality due topartial stenosis of the herl1iated gut at thediaphragmatic tear, causing an accumu­latioIl of gas.

As witl1 auscultation of the heart, obesi­ty, pneumothorax and pleural effusionswill affect the intensity of the pulmonarysounds. Thorough auscultation of the pul­monary area, however, will often aid inan accurate diagnosis of any condition.

Auscultation of the abdomen is a val­uable tool in large animal medicine. Rou­tine auscultations are carried out 011 theright and left paralumbar fossae and mid­way down the posterior portion of the ribcage on both sides.

Ruminal sounds heard in the left para­lumbar fossa consist of two parts. Thefirst sound is sin1ilar to bubbling fluid

5

7

Figure 3. Systematic auscultation of the thorax.

as mucus and other forms of exudate andtransudate are present in the bronchi. Dryrales result when tenacious materials andfairly dry exudates occur in the same pas­sages and usually indicating some degreeof chronicity. Vesicular sounds, oncethought to be transmitted from the areaof the pharynx (31) , are created as airn10ves in and out of the alveoli from thetiny bronchioles. Vesicular and bronchialsounds are those heard upon auscultationof a normal IUl1g.

When lung pathology is present, com­binations of the other sounds usuallyoccur. Early bacterial bronchial pneu­monia is usually characterized by in­creased vesicular sounds followed by moistrales. As the lesions regress, dry ralesbecome more prominent. It is always wiseto keep in mind, however, that all threemain types of sounds, with several grada­tions of each, may often be found in thelungs of one patient dUril1g one examina­tion. Haematogenous bacterial pneumoniawill o£ten pJ."loduce lung abcesses. If theseare fairly large, they may be isolated onauscultation as there is a central areaof little or no sound surrounded by areasof rales.

Parasitic lungworm pneumonias alsocause a bronchitis but here differentialdiagnosis depends 011 the location of thefirst pathological sounds. This form ofbronchitis is usually complicated by sec­ondary pneumonia. Virus pneumonia, onthe other hand, if not contaminated by asecondary bacterial pneumonia, is charac-

70 Iowa State U11iversity Veterinarian

while the second is similar to distant thun­der. At least one ruminal movementshould occur every three minutes or rumi­nal stasis can be suspected. The normalrumen rolls about three times per minute.Reticular contractions can often be de­tected low down in the seventh intercostalspace on the left side. These sounds areusually bubbly in character and may bevery faint in obese subjects. The hollowtinkling sounds heard just posterior to themiddle and distal thirds of the last rib onthe left side are usually considered pathog­nomonic for displacement of the aboma­sum. Care should be used in the interpre­tation of these sounds however, in ordernot to confuse them with bubbles of gasrising in the ruminal ingesta. The formersounds have a much more hollow qualitythan the latter.

Intestinal sounds are frequently heardin the right paralumbar fossa. These areusually faint fine sounds and only per­ceivable following careful use of the steth­oscope in this region. Increase in frequen­cy and intensity of intestinal sounds isoften the r-esult of an illflammed intestinaltract. Little is known of the exact originof intestinal noise except that it originatesfrom the bowel (2). Abnormal intestinalsounds are most frequently heard as a re­sult of obstructions of paralytic ileus.Tympanitic sounds usually indicate bub­bles rising in a partially fluid filled viscoussuch as anterior to an obstruction. It mustbe emphasized, howevelr, that sounds sim­ilar to tllese are heard ill the normal ab­domen. An example of the latter is thetympanitic drops heard as fluid dropsfrom the ileocaecal valve into the fundusof the caecum of the horse.

In the practice of medicine, whether itbe large animal, small animal, or human,a prerequisite to an accurate diagnosis isa careful and complete physical examilla­tion of the patient. Auscultation is one ofthe important tools used in such an ex­amination. The interpretation of thesounds heard then depends on an under­standing of the basic medical sciencessuch as pathology and physiology, as wellas experience. Experience is gained bydiligent practice; thus the more a cliniciallapplies the use of his stethoscope to medi-

Issue, No.2, 1962-63

cal practice, the more will he benefit fromits use.

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24. Leopold, S. s.: The Principles and Methods ofPhysical Diagnosis. W. B. Saunders. London.

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33. Moore, S. W.: The Physiological Basis forDiagnostic Signs of an Acute Abdomen. SurgeClin. North America 38 (2): (1958)

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35. Murashko, V. V.: Apparatus for the Intensifi­cation of Auscultatory Sound. Clin. Med.(Mosk.) 37: 135-137.

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39. Saureage, F.: Auscultation and Percussion ofthe Digestive System in Cattle. Thesis, Paris(Alfort) p. 48.

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42. Snelen, H. A.: Phonocardiography and Vector­cardiography in the Diagnosis of Heart Dis­ease. N"ed. T. Ganeesk 106: 328-220. (1962)

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45. Vogelpoel, L.: Pulmonary Stenosis, Assessmentby Auscultation and Phonocardiography. Amer.Heart. 59: 645-666. (1960)

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