Breath Sounds
Introduction
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 Objectives
By the end of this tutorial you should be able to identify and understand the
clinical relevance of the following breath sounds:
•
Normal breath sounds
•
o
o
o
o
o
Abnormal breath sounds:
Bronchial Breathing
Stridor
Wheeze
Crackles
Pleural rub
Breath Sounds, Page 1
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 lowpitched components.
Normal lung
Normally inflated alveoli filter out high-pitched components and transmit lowpitched 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.
Breath Sounds, Page 2
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 sounds
There 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.)
Breath Sounds, Page 3
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 highpitched 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 Effusion
In 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.
Breath Sounds, Page 4
Interesting Fact:
Normal breath sounds are described as ‘vesicular’ because it was once
thought that they arose in the vesicles (alveoli)
Abnormal Breath Sounds
In 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
Breath Sounds, Page 5
•
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
Lymphoadenopathy
Bilateral vocal cord
palsy
Laryngospasm
Post-op
Croup
Following neck surgery
Acute epiglottitis
Amyloidosis
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).
Breath Sounds, Page 6
ATS
Nomenclature
Also know as
Acoustic
characteristics
Laënnec’s description
(1819)
Coarse Crackles
Coarse
crepitations
Discontinuous,
interrupted explosive
sounds
Loud
Low pitch
Escape of water from a
bottle with mouth held
directly downwardsFine
Crackles
Fine Crackles
Fine crepitations
Discontinuous,
interrupted explosive
sounds
Less loud and shorter
duration
High pitch
Repetitive
Prolonged whisper,
chirping of birds
Wheeze
High-pitched
wheeze
Continuous sounds,
longer than 250ms
High pitch
Dominant frequency of
≥400 Hz
Prolonged whisper,
chirping of birds
Rhonchus
Low-pitched
wheeze
Continuous sounds,
longer than 250ms
Low pitch
Dominant 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.
Breath Sounds, Page 7
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.
Breath Sounds, Page 8
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.
Crackles
Crackles 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 Cause
Early
Small airway disease (e.g. bronchiolitis)
Middle
Pulmonary oedema
Late
Pulmonary fibrosis (fine)
Pulmonary oedema
Bronchial secretions in COPD, pneumonia, lung abscess,
tubercular lung cavities (coarse)
Biphasic
Bronchiectasis (coarse)
Breath Sounds, Page 9
Coarse Crackles
Coarse 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 Crackles
Fine 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
Breath Sounds, Page 10
•
•
Cystic fibrosis
Pneumonic consolidation
Early Inspiratory Crackles
Early 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 Crackles
Late 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
Breath Sounds, Page 11
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 Sounds
Reduction 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:
Breath Sounds, Page 12
•
•
•
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.
Breath Sounds, Page 13
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
Breath Sounds, Page 14