There are four questions to be asked during the auscultation phase of the chest exam:
Which type of breath sound is heard at this site?
What is the intensity of the breath sounds at this site?
Are there any adventitious (added) breath sounds present at this site?
Are there any sites manifesting abnormal voice transmission?
In a quiet room, the patient is asked to breathe deeply, but with an open mouth, as the stethoscope diaphragm is pressed firmly against the skin to survey the anterior and posterior chest walls systematically with the sequential ladder pattern approach. At each site being auscultated, the physician should determine the type of breath sound present, its intensity, and whether there are any extra adventitious breath sounds. After completing auscultation of a patient's normal breath sounds, auscultation during vocalization is done if clinically warranted (see below).
Interpretation of Breath Sound Type
While three types of breath sounds have been described (vesicular, bronchovesicular, and bronchial) new students should learn two: vesicular and bronchial. Vesicular breath sounds are the normal breath sound heard over healthy lung fields. They are muted, low-pitched, and characterized by an inspiratory:expiratory (I:E) duration of about 3:1. This ratio occurs because expiratory sounds normally end well before the actual expiratory phase of respiration has ceased. Bronchial breath sounds are a normal finding only over the sternal manubrium. They are louder than bronchovesicular breath sounds, have a higher pitch, and their I:E is <1. Bronchial breath sounds also tend to be harsher than vesicular sounds, and are occasionally called tubular breath sounds by clinicians who consider their sound to resemble that of air passing through a tube.
Interpretation of Breath Sound Intensity
With practice, students can expand beyond a beginner's simple intensity dichotomy of "presence or absence" of sound to a standardized breath sound scoring system having five tiers. The most common scoring system applied to breath sounds is: absent (0 points); barely audible (1 point); faint but definitely heard (2 points); normal (3 points); and louder than normal (4 points). This five-tiered system is applied at six defined points on the patient's thorax: bilaterally on the upper anterior chest wall, bilaterally in the mid-axillary line, and bilaterally on the lower posterior chest wall. Thus, an aggregate score generated for the entire chest ranges from 0 points (breath sounds absent at all sites) to 24 points (breath sounds louder than normal at all sites), with normal being defined here as 18 points.
Interpretation of Adventitious Sounds
The abnormal breath sound most usually termed crackles (or rales) is a series of short (5-30 msec), discontinuous notes that have been likened to the sound produced by the pulling apart of strips of Velcro®, or the sound of longer hair strands being rubbed together. Some physicians distinguish two categories of such sounds: fine crackles that are more muted and higher-pitched than coarse crackles, which are louder, lower-pitched, and fewer per breath. Independent evidence that these two levels of crackles differentially assist in the diagnosis of specific diseases is lacking. A different characteristic of crackles that does have diagnostic utility in certain situations is their inspiratory timing. Early inspiratory crackles do not persist into the second half of inspiration, and are more typical of obstructive airway diseases (Chap. 22). Late inspiratory crackles continue throughout the inspiratory phase and often suggest diseases of the lung parenchyma such as alveolar edema in heart failure or ARDS (Chap. 28).
A wheeze is a continuous adventitious sound that lasts much longer (~250 msec) than an individual crackle, is musical in quality, and often is high-pitched. Wheezes usually occur during expiration, but are sometimes present during both inspiration and expiration. They are a manifestation of narrowing in the smaller airways of the lung causing increased airflow resistance, signifying that a patient most likely has an obstructive airway disease such as COPD or asthma. However, absence of wheezing does not exclude either COPD or asthma, because most of these patients do not wheeze when their disease is well-controlled, or conversely when their airway obstruction is so severe such that little air movement is occurring.
The term rhonchus (plural: rhonchi) presents students with the challenge of interpreting an adventitious breath sound with a name that is not used consistently within the profession. As defined by the American Thoracic Society, rhonchi are continuous adventitious sounds lasting ~250 msec and are low-pitched in tone. Despite this definition, the term rhonchi is applied inconsistently even by experienced clinicians. It is therefore recommended that new students avoid the term, and instead classify all continuous sounds as either a high-pitch wheeze or a low-pitch wheeze.
Stridor is a continuous, loud, adventitious sound of constant pitch that is acoustically similar to a wheeze. Stridor is distinguished from wheeze by two criteria: (1) stridor is louder over the neck, while wheezes are louder over the chest wall; and (2) stridor occurs during inspiration while wheezes can occur throughout the respiratory cycle. Stridor is caused by high-grade obstruction of the upper airway, and represents a medical crisis. Physicians-in-training hearing what they believe is stridor should seek immediate assistance since the patient's airway may need to be secured emergently.
A pleural rub is a sound of variable intensity that suggests grating of the visceral and parietal pleural surfaces that normally slide silently against one another. Although some pleural rubs have phonic components that sound like crackles, the creaking or crackling of a rub is more often heard during inspiration than expiration. The presence of a pleural rub indicates the patient has a disease that involves inflammation of the pleurae.
Method: Voice Sound Transmission
When auscultating over normal lung fields, a patient's voice is muffled and unintelligible. Several terms have been introduced to signify abnormal voice transmission. Bronchophony indicates that voice sounds are louder than normal, whether or not they are intelligible. Pectoriloquy is used to indicate that words are intelligible by auscultation, and whispered pectoriloquy if intelligible even at very low spoken sound volume. Egophony is a change in the timbre of the vowel sound "EE", giving it a nasal quality that sounds more like "AA" or "AH". In the United States, egophony is often called an "E to A Change".
Abnormal voice transmission suggests that the patient has either pneumonic consolidation or a large-volume pleural effusion with compressive atelectasis. These two possibilities can be distinguished because consolidation increases tactile fremitus while a pleural effusion decreases fremitus except at the top of a large effusion where there may be a zone of increased fremitus. In many cases, altered voice sound transmission is accompanied by bronchial breath sounds, as both are caused by enhanced transmission of sounds from the central airways to the chest wall through consolidated lung.