Breath SoundsIntroduction

This tutorial is an introduction to Breath Sounds.

It gives you an opportunity to listen to both normal and abnormal breath sounds, as well as explaining their clinical relevance.

It would be most useful to study this tutorial at the beginning of your Medicine and Surgery placement with a view to increasing both your confidence and competence levels when auscultating a patient’s chest.

Alternatively, you could use this tutorial as a revision aide when preparing for your Long Case or to review and refresh before your Final examination.

It is assumed that you already know how to examine a patient’s chest.

If you need any further guidance on how to do a chest examination, then please refer to ‘Macleod’s Clinical Examination’. It has extremely good instructions and comprehensive explanations on clinical examination. It usually comes with a CD that contains a video on ‘Respiratory Examination’.

Aims and ObjectivesBy the end of this tutorial you should be able to identify and understand the clinical relevance of the following breath sounds:

• Normal breath sounds

• Abnormal breath sounds: o Bronchial Breathingo Stridoro Wheezeo Crackleso Pleural rub

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Physiology and Ausculation

Turbulent airflow in the trachea and proximal bronchi causes vibration of the solid tissues and fluctuation of the intra-luminal pressure. This is what creates the sound in your stethoscope.

Smaller distal airways and alveoli have laminar flow, which is slow and silent.

During quiet breathing, the larynx makes no significant contribution to the breath sounds. However, in deep breathing, it may accentuate the breath sounds.

Sound transmission in the lung The sound that travels up and down the trachea contains both high- and low-pitched components.

Normal lungNormally inflated alveoli filter out high-pitched components and transmit low-pitched components, giving breath sounds their so-called ‘vesicular’ quality.

The Intensity and quality of the breath sounds depends on the position of your stethoscope and its distance from the point of origin. So, if you auscultate over the trachea, the breath sounds will be loud and will contain all frequencies. The same is true when listening to the anterior lobes of a thin patient.

However, when you move your stethoscope further away from the trachea, breath sounds become quieter because the high-pitched sounds are filtered out by the alveoli.

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When you are auscultating the chest, make sure that you listen for the attenuation of the breath sounds from top to bottom as well as the differences in intensity between the two sides.

Breath sounds that are louder at the bases indicate abnormality!

Effects of respiratory disease on breath soundsThere are two ways in which respiratory disease can affect breath sounds:

1. It interferes with the alveolar filter (e.g. consolidation)2. It reduces the intensity (loudness) of the breath sounds (e.g. pleural effusion)

Let’s look at this on a schematic diagram. (Please bear in mind that the representation of consolidation and pleural effusion is not pathologically accurate. This diagram is just to help you visualise the changes in sound transmission depending on the disease.)

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First of all, look at the normal lung (RED). You can see that low-pitched sounds are transmitter unaltered, whereas high-pitched sounds are completely filtered out.

Now, let’s compare that to the consolidated lung (GREEN) and to the pleural effusion (BLUE).

Consolidated lung

As you can see from the diagram, consolidated lung (GREEN) transmits high-pitched sounds and filters off some of the low-pitched sounds. This is why you hear bronchial breathing, which is composed of loud, high-pitched breath sounds.

Pleural EffusionIn pleural effusion, the sound waves are reflected at the air-fluid interface, leading to a reduction in transmission of ALL sounds. When auscultating a patient’s chest, you will notice the absence of or a reduction in breath sounds on the affected side.

Normal breath sounds

We will begin by listening to normal breath sounds, which are commonly described as ‘vesicular’, referring to their ‘rustling’ character.

While watching the video and listening to these breath sounds, compare the inspiratory and expiratory phases – the expiratory phase is softer and shorter than the inspiratory phase.

During expiration, normal breath sounds fade rapidly as airflow decreases and there should be no gap between inspiration and expiration.

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Interesting Fact:

Normal breath sounds are described as ‘vesicular’ because it was once thought that they arose in the vesicles (alveoli)

Abnormal Breath SoundsIn this section, you will learn about abnormal breath sounds:

• Bronchial breathing• Stridor• Wheeze• Crackles• Pleural rub

Bronchial Breathing

Unlike normal respiration, in bronchial breathing the high-pitched sounds are NOT filtered out, giving the breath sounds a hollow or blowing quality. It is similar to what you would normally hear over the trachea and the main bronchi.

In bronchial breathing, the length and intensity of inspiration and expiration are equal, and there is a characteristic pause between them.

For bronchial breathing to be present, the bronchus to the diseased area MUST be patent. Bronchial breathing, therefore, tends to exclude the possibility of an obstructing lung cancer!

Bronchial breathing indicates abnormal function of the alveolar filter present in

• Consolidation• Collapsed lung/lobe

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• Dense fibrosis

It can also be heard above a pleural effusion

Stridor

Stridor is a noisy inspiratory sound caused by a partial obstruction of the upper airways.

Causes of stridor

Obstruction within lumen of airway

Obstruction within wall of airway

Extrinsic obstruction

Foreign body Oedema from anaphylaxis

Goitre

Tumour Tumour LymphoadenopathyBilateral vocal cord palsy

Laryngospasm Post-op

Croup Following neck surgeryAcute epiglottitisAmyloidosis

Remember!

Stridor is an EMERGENCY, especially in children.

Classification of Wheeze & Crackles

There are many ways to classify both wheeze and crackles.

In the table below, you can see a classification devised by the American Thoracic Society (ATS), in addition to the original description of these sounds by Laënnec in 1819 (although not entirely accurate anymore).

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ATS Nomenclature

Also know as Acoustic characteristics

Laënnec’s description (1819)

Coarse Crackles Coarse crepitations

Discontinuous, interrupted explosive soundsLoud Low pitch

Escape of water from a bottle with mouth held directly downwardsFine Crackles

Fine Crackles Fine crepitations Discontinuous, interrupted explosive soundsLess loud and shorter durationHigh pitchRepetitive

Prolonged whisper, chirping of birds

Wheeze High-pitched wheeze

Continuous sounds, longer than 250msHigh pitchDominant frequency of ≥400 Hz

Prolonged whisper, chirping of birds

Rhonchus Low-pitched wheeze

Continuous sounds, longer than 250msLow pitchDominant frequency about ≤200 Hz

Snoring, cooing of a wood pigeon

Wheeze

Wheeze is a whistling or sighing sound. It is caused by the vibration of the airway walls and adjacent tissues in a narrowed airway. When the airway narrows, the airflow accelerates, reducing the pressure in this airway. This causes the airway to close and leads to subsequent reduction in the airflow. As the airflow reduces, the airway reopens again. This rapid vibration generates the wheeze.

Pitch depends on the elasticity and the mass of these tissues, not the size of the airway.

Normal airways dilate on inspiration and narrow during expiration. That’s why wheeze tends to be louder on expiration.

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As a general rule, diffuse wheeze is a feature of asthma or COPD, whereas wheeze localised to one side or one area of the lung indicates bronchial obstruction by a cancer (adult) or a foreign body (child).

Some research suggests that you can judge the severity of the disease by the proportion of the respiratory cycle occupied by the wheeze. The longer the wheeze the lower the FEV1 value is, indicating a more severe disease.

Fixed monophonic wheeze

Fixed monophonic wheeze is a single note of constant pitch, timing and site. It is caused by a high-velocity airflow through a localised narrowing of one airway. It cannot be abolished by coughing.

Think Bronchial carcinoma (the most common cause)!

Ask the patient to lie on their side – if a tumour or other organic narrowing is present, the wheeze will be altered. The character of the altered wheeze depends on the location of the narrowed bronchus.

If it is in the upper lung, then lying on the side will increase the distending forces acting upon that bronchus and cause it to expand, resulting in the disappearance of the wheeze.

If it is in the lower lung, then lying on the side will exacerbate the airway narrowing, resulting in accentuation of the wheeze. However, if the bronchial narrowing is critical, then lying on the side may cause complete obstruction, leading to the absence of wheeze and breath sounds.

Monophonic wheeze can rarely be caused by mucus partially blocking one airway – i.e. Asthma or COPD. Ask the patient to cough – if mucus is the cause, then the wheeze will disappear.

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Polyphonic wheeze

Polyphonic wheeze is made of many different notes, representing each airway at the point of closure. It occurs in inspiration and expiration.

It is characteristic of asthma and COPD. (However, patients with severe COPD may have no wheeze because of low rates of airflow.)

Remember:

Silent chest (absence of wheeze in a patient with acute asthma) indicates a life-threatening asthmatic attack. Prompt treatment saves lives!

It is caused by severe bronchospasm preventing adequate air entry.

CracklesCrackles are brief, interrupted, non-musical, explosive sounds.

There are 2 theories regarding the mechanism behind crackles:1. Bubbling of air through airway secretions (coarse crackles)2. Explosive re-opening of airways whose walls have become abnormally apposed during expiration (fine crackles)

Classification of Crackles

Crackles can be either classified on the basis of the quality of the sound (Coarse and Fine) or the phase of the respiratory cycle.

Phase of inspiration CauseEarly Small airway disease (e.g. bronchiolitis)Middle Pulmonary oedemaLate Pulmonary fibrosis (fine)

Pulmonary oedema Bronchial secretions in COPD, pneumonia, lung abscess, tubercular lung cavities (coarse)

Biphasic Bronchiectasis (coarse)

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Coarse CracklesCoarse crackles are thought to be caused by air bubbling through the mucus in the large airways.

Coarse crackles have an explosive, gurgling quality and are modified by taking deep breaths or by coughing (except in bronchiectasis). They can also be heard away from the affected area and by holding a stethoscope to the patient’s mouth.

Coarse crackles are associated with

• COPD• Pneumonia• Lung abscess• TB cavities• Bronchiectasis

Fine CracklesFine crackles are explosive high-pitched sounds that occur in each cycle in mid/late inspiration and are repeated in subsequent cycles. Each crackle occurs at a particular transpulmonary pressure and represents a reopening of a previously closed small airway.

Unlike coarse crackles, fine crackles do NOT change after coughing or deep breathing.

Fine crackles resemble the sound of dry hair rolled between the fingers close to the ear.

Fine crackles are associated with

• Pulmonary fibrosis• Pulmonary oedema• Allergic alveolitis• Bronchiectasis

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• Cystic fibrosis • Pneumonic consolidation

Early Inspiratory CracklesEarly inspiratory crackles are heard at the beginning of inspiration.

Early inspiratory crackles are associated with diseases that lead to airflow obstruction, such as COPD and also occur in bronchiolitis They are best heard at the lung bases and usually disappear when the patient is asked to cough.

Late Inspiratory CracklesLate inspiratory crackles are associated with reduced lung compliance (increased stiffness) that is not uniformly distributed. During inspiration, the air first enters the more compliant parts of the lung. Later in inspiration, as elastic recoil forces build up in the stretching lung, the air eventually enters the stiffer parts of the lung. This explosive reopening of the small distal airways is the proposed cause of late inspiratory crackles

These crackles are gravity depended, so in the upright position they are best heard at the lung bases.

If you auscultate the bases of the lung in an elderly patient first thing in the morning, you may hear repetitive late inspiratory crackles. These are gravity dependent crackles that will disappear after a few deep breaths.

Late inspiratory crackles are associated with

• Interstitial fibrosis• Pneumonia• Pulmonary oedema• Alveolitis • Asbestosis

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Biphasic Crackles

Biphasic crackles occur in both inspiration and expiration. They are a combination of coarse and fine crackles

Biphasic crackles are a feature of bronchiectasis and are related to a combination of secretions and increased compliance of the walls in larger airways.

Pleural rub

Pleural rub is described as a ‘creaking’, coarse, grating or leathery sound, and is similar to the sound of bending stiff leather or treading in fresh snow.

It is often localised and is best heard with the diaphragm of your stethoscope low in the axilla or over the lung bases (posteriorly).

Pleural rub tends to recur at the same moment in each respiratory cycle, often in both inspiration and expiration. It is not altered by coughing. However, when it is confined to inspiration it may be impossible to distinguish from repetitive inspiratory crackles.

It is caused by friction between inflamed visceral and parietal surfaces of the pleura.

Pleural rub is usually associated with pleuritic pain and may be heard over areas of inflamed pleura in pulmonary infarction, pneumonia or vasculitis.

Absent or Reduced Breath SoundsReduction in the intensity (loudness) of breath sounds is commonly described as reduced ‘air entry’.

It can be generalised or localised.

Causes of generalised reduction in intensity of breath sounds include:

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• Obesity• Hyperinflation of the lungs (e.g. COPD)• Hypoventilation (e.g. life-threatening asthma)

Causes of localised reduction in breath sounds include:• Bronchial occlusion (preventing air entry into a lobe)• Collapsed lung or lobe• Pleural effusion or pneumothorax (causing reflection of the sounds)• Unilateral paralysis of the diaphragm or intercostal muscles (causing reduced ventilation)

Summary

1. When the air travels down your trachea it creates a sound, which is a combination of high-pitched and low-pitched components. High-pitched components are filtered out by the normal alveoli. Normal breath sounds are louder at the apices. Inspiration is longer than expiration and there is no gap between these phases.

2. In pleural effusion, there is reflection of the sound waves leading to the reduction in transmission of all breath sounds.

3. Important causes of absent/reduced breath sounds are: hypoventilation, bronchial occlusion, collapsed lung/lobe, pneumothorax, pleural effusion.

4. In consolidated lung, high-pitched sounds are transmitted and some of the low-pitched sounds are filtered out, producing bronchial breathing. Causes of bronchial breathing include: consolidation, collapsed lung/lobe, dense fibrosis or listening above a pleural effusion.

5. Stridor is an emergency. Some of the causes of stridor are: tumour, foreign body, vocal cord palsy, anaphylaxis.

6. Wheeze results from the vibration of the airway walls in a narrowed airway. The commonest cause of Monophonic wheeze is Bronchial carcinoma. Polyphonic wheeze is characteristic of asthma.

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7. Coarse Crackles are caused by air bubbling through the mucus in large airways. These are associated with COPD, pneumonia, lung abscess, TB lung cavities and bronchiectasis

8. Fine crackles are caused by the explosive reopening of a previously closed small airway. These are associated with pulmonary fibrosis, pulmonary oedema, allergic alveolitis, bronchiectasis, cystic fibrosis and pneumonia.

9. Biphasic crackles occur in both inspiration and expiration and are a feature of bronchiectasis.

10. Pleural rub is caused by friction between inflamed visceral and parietal pleura. It is associated with pulmonary infarction, pneumonia and vasculitis

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