Auscultation of Breath Sounds in IPF

Introduction

Auscultation of the lungs is an important component of a physical examination because respiratory sounds provide vital information regarding the physiology and pathology of lungs.^1,2 The ability to distinguish normal breath sounds from various abnormal adventitious sounds is essential to make an accurate medical diagnosis.^1,2 Breath sounds are generated by airflow in the respiratory tract and include normal and adventitious sounds.^1,2 Adventitious sounds are additional respiratory sounds superimposed on normal breath sounds and usually indicate pulmonary disorders.^1,2 For many years a complex, conflicting, and confusing body of terms was used to describe respiratory sounds.³ In order to establish a more objective naming system, in 1985 an ad hoc committee of the International Lung Sounds Association agreed on a nomenclature that divided adventitious sounds into 2 major categories: continuous sounds and discontinuous sounds (Table 1).³ These terms are defined acoustically (e.g., frequency, duration, initial deflection width, etc.) and do not assume a generating mechanism or location.^4,5

Table 1.

Lung Sound Nomenclature. Adapted from Mikami R, et al. Chest. 1987;92:342-345.

BREATH SOUNDS OF IDIOPATHIC PULMONARY FIBROSIS (IPF)

Bilateral fine crackles on chest auscultation are detected in most patients with IPF and can be heard before any radiologic findings.^1,6 These crackles are heard during middle to late inspiration and have a short, explosive and nonmusical quality.¹ They tend to be heard almost exclusively over diseased areas and are not affected by coughing.^1,7 The sounds may change or suddenly disappear when the patient bends forward, since fine crackles are gravity-independent.^1,8 Fine crackles are generated when previously collapsed alveoli suddenly reopen during late inspiration.⁸

Fine crackles are an important and early sign of IPF that can help with differential diagnosis.¹ It is typically heard in the lung bases first, then become detectable at the upper zones as disease progresses.¹ It is important to note that fine crackles are not pathognomonic of IPF as they can be also heard in other interstitial lung diseases (ILDs) such as connective tissue disease associated ILDs, asbestosis and nonspecific interstitial pneumonitis.¹

Listen to the examples below to hear breath sounds recorded from patients with IPF.

Normal Breath Sounds

Normal breath sounds are characterized by a soft, nonmusical noise heard during inspiration and only in the early phase of expiration.¹ The inspiratory component of the sound is mostly generated within the lobar and segmental airways while the expiratory component is produced from more central areas.^1,5 Air turbulence is one mechanism thought to generate normal lung sounds.^1,5

In clinical practice, diminished breath sound intensity from decreased inspiratory flow is the most commonly seen abnormality.¹ This can be due to several different conditions such as depressed central nervous system, airway narrowing due to a foreign body, a tumor or airway diseases (e.g., asthma and chronic obstructive pulmonary disease).¹

Listen to the examples of normal breath sounds.

References