Breath Sounds and Its Association with Disorders

Introduction:

Pathological signs and symptoms are essential criteria for the assessment of underlying disorders. Inspection, palpation, percussion, and auscultation are the traditional methods for diagnosing conditions. Ausiliation of the respiratory system is an inexpensive method to determine the pathological conditions involving respiratory systems. It is also one of the age-established methods for disease identification. The first use of this method was advocated by Hippocrates. In the old days, doctors placed their ears over the chest to hear different breathing sounds. Later in 1816, Rene Theophile Hyac invented the stethoscope which made the job of auscultation much easier. With the help of modern stethoscopes, it is much easier to identify different breathing sounds in different pathological conditions.

What Is the Mechanism of Breathing Sounds?

In the normal scenario, air maintains a uniform laminar flow inside the airway tract. The laminar flow is parallel to the surface of the airway tract and the nature of the flow is parabolic in nature. The central portion of the airflow moves much faster than the peripheral flow. As a result, any type of laminar flow and intermixing in between the flow. This flow of air follows a Poiseuille equation. In peripheral airways and in smaller airways air moves at a much faster speed. But here also, linear flow is maintained.

In this condition, the flow rate is equivalent to the pressure and radius of the airway tract. The flow rate of the air is inversely proportional to the density of the air. When high-velocity air is passed through the wider diameter of the airway or there are irregularities in the airway tract sound is produced. These factors produce turbulency associated with the collision between air particles and are responsible for noise production. The normal sound detected during the breathing process is of three types, normal tracheal sound, normal lung sound or vesicular breath sound, and bronchial breath sound. Three types of bronchial breath sounds are tubular sound, cavernous sound, and amphoric sound.

These sounds are produced by various factors. These are:

• Development of the vortices is associated with the whirlpool motion of the air. These motions are generally formed at the terminal bronchi.
• The lung sounds are produced by the change in the pressure and shape of the lung and the chest wall produced during the respiratory process. The sounds produced during this process are low-frequency sounds. The usual frequency of these sounds is between 100 to 200 Hertz. The lung parenchyma and the chest wall prevent high-frequency sounds to pass and act as filters. That is why, only low-frequency sounds are heard.
• The sounds that are associated with respiration are heard in the early phases of respiration and also in the inspiratory phase. The generation of turbulence as the air moves up in the wider central airways is the reason behind the sound in the expiratory phase. The inspiratory sound is heard in the segmental and lobar airways. The characteristics of the lung sounds are:

1. These sounds are soft and low-pitched.
2. The inspiratory phase of the sound lasts longer than the expiratory phase.
3. The intensity and pitch of the inspiratory phase are higher than the expiratory phase.
4. These sounds are audible in the posterior lung air bases.

• Bronchial sounds are also known as tubular sounds. The frequency of such sounds is relatively higher. Such sounds are most commonly heard over large airway spaces. These sounds are mainly heard in between the second and third intercostal space. Posteriorly such sounds can be heard between the seventh cervical vertebrae and third thoracic vertebrae. The features of these sounds are:

1. These sounds are loud, hollow, and high-pitched.
2. Contradictory to the lung sounds expiratory phases of these sounds are longer than the inspiratory phase. Also, a distinct pause between the two phases can be heard.
3. Pathological factors are associated with the presence of tubular sound, cavernous sound, and amphoric sound.

• The intermediate sounds that are heard between bronchial and lung (vascular) sounds are known as broncho vascular sounds. These sounds are normally heard in between the first and second intercostal space (between the first and second ribs).
• The tracheal sounds are heard over the supra sternal area. The usual frequency of the tracheal sounds varies from 100 to 1500 Hertz. The nature of these sounds is harsh, loud, and high-pitched. These sounds are accessed to detect the presence of an obstruction in the upper respiratory tract.

What Are the Adventitious Lung Sounds?

The additional respiratory sound that is heard along with breath sounds are known as adventitious lung sounds. The duration of continuous adventitious lung sounds is less than 250 milliseconds. Another type of adventitious sound is an interrupted sound or discontinuous sound.

In different pathological conditions, different adventitious breathing sounds can be heard. These are:

Wheeze:

These sounds are produced by the limitations or the obstruction of the airflow. These are high-pitched continuous sounds with a frequency of more than 400 Hertz. If the frequency is less than 200 Hertz, it is called rhonchi. Wheeze is mainly expiratory in nature but it can be inspiratory also. Wheezes can be heard in open-mouth conditions or over the tracheal regions. Ronchi can be heard over the chest wall. Short inspiratory wheezes are known as squawks. The frequency of squawks is ranged between 200 to 300 Hertz. These sounds can be heard in the late phase of inspiration.

Crackles:

Discontinuous, explosive, and nonmusical adventitious lung sounds heard during inspiration are known as crackles. The duration of crackles is less than 20 milliseconds. Crackles are formed due to the passage of the air through the bronchial secretions. Accumulation of the air in the small and medium airways produces these bubbling sounds. Based on loudness, pitch, and timing crackles can be divided into fine and coarse crackles.

Stridor:

These are the loud and high-pitched sounds heard due to the obstruction of the upper respiratory tract. These sounds can be heard in the neck and chest wall regions. These sounds are also biphasic in nature. Though these types of sounds are mainly inspiratory in nature.

Pleural Rub:

These are short, explosive, and rubbing types of sounds. These are produced by friction between two layers.

What Are the Conditions Associated with Adventitious Lung Sounds?

The abnormal conditions which are associated with different types of breath sounds are:

Hyperinflation, pneumothorax (collection of air outside the lungs), and pleural effusion (accumulation of fluid in between two layers of pleura) are associated with diminished breath sounds.

Wheezing is associated with conditions like chronic obstructive pulmonary disorder (COPD). Also, airway obstructions due to tumors are associated with wheezing. Pulmonary fibrosis and hypersensitivity pneumonitis (allergic infection of the lungs) are associated with squawks. Squawks can also be detected in cases of lung pneumonia.

Crackles are heard in conditions like pulmonary edema (accumulation of fluid in the lungs), interstitial lung disease (group of disorders causing lung fibrosis), and heart failure. Bronchiectasis (a condition associated with the widening of the airway), chronic obstructive pulmonary disorders, and idiopathic pulmonary fibrosis (IPF) are responsible for crackles.

Conditions like pulmonary embolisms and pleurisy (infection of the pleura) are associated with pleural rub.

Conclusions:

Pathological signs and symptoms are important diagnostic methods for disease identification. Assessment of breath sounds is an age-old method of detecting lung conditions. The normal flow of the air produced breath sounds within the normal physiological limits. But, pathological conditions are associated with the formation of different sounds like wheezing, crackles, and rubbing.