Auscultation is the process of listening to sounds from the body, typically using a stethoscope. In the context of respiratory assessment, listening to lung sounds provides a simple, non-invasive method to evaluate airflow through the trachea and bronchial tree. The sounds generated by air moving in and out of the lungs offer valuable insight into the condition of the airways and surrounding lung tissue. Understanding how to correctly perform this technique and interpret the basic sounds is the first step in recognizing normal respiratory function and potential deviations.
Preparation and Essential Equipment
The primary piece of equipment needed is a stethoscope, a device that amplifies internal body sounds. Stethoscopes typically feature a dual-sided chest piece consisting of a bell and a diaphragm. The flat, larger diaphragm is designed to pick up higher-frequency sounds and is the preferred surface for listening to generally high-pitched lung sounds. The smaller, cup-shaped bell detects lower-frequency sounds, such as certain heart murmurs.
The environment must be quiet to ensure the subtle sounds are not obscured by background noise. The person being assessed should be sitting upright in a comfortable position, which allows for the full expansion of the lungs and access to all listening points. The stethoscope must be placed directly onto the skin, as clothing can create friction sounds that interfere with the true lung sounds.
Systematic Technique for Lung Auscultation
A successful lung assessment relies on a systematic approach to ensure all areas of the lung fields are checked. The person should be instructed to breathe slightly deeper than normal and consistently through their mouth, as this increases the airflow and makes the sounds clearer. The diaphragm of the stethoscope must be pressed firmly enough against the skin to create a seal, but not so hard as to cause discomfort. Listening to at least one full breath cycle—inspiration and expiration—at each point is necessary for an accurate assessment.
The listening points should be followed in a side-to-side, top-to-bottom pattern, comparing symmetrical locations on the left and right sides. Begin with the anterior chest, starting just above the collarbones (apices) and moving downward between the ribs. Next, assess the lateral sides, starting high in the armpit area and moving down to the lower ribs.
The posterior back provides the best access to the lower lobes of the lungs. Use a ladder pattern, starting at the shoulders and moving side-to-side and down. Place the stethoscope in the spaces between the spine and the shoulder blades to prevent sound muffling. This methodical comparison allows for the detection of differences in sound intensity or quality between the two lungs.
Characteristics of Normal Breathing Sounds
Normal breathing sounds provide the baseline against which any deviations are measured and are categorized by their pitch, intensity, and duration. The most common sound heard over the majority of the lung fields is the vesicular breath sound. These sounds are soft and low-pitched, often described as a gentle rustling, and they are produced by the turbulent flow of air in the smaller airways.
Vesicular sounds are characterized by inspiration being longer, louder, and higher-pitched than expiration, flowing seamlessly without a noticeable pause. Bronchial sounds are normally only heard over the trachea and main stem bronchi. These sounds are louder, harsher, and higher-pitched, and the expiration phase is longer and louder than the inspiration phase, with a slight pause between the two.
Understanding Adventitious Lung Sounds
Adventitious sounds are any sounds heard in addition to the expected normal breath sounds and suggest a change in the airflow or the condition of the lung tissue. The most frequently encountered adventitious sounds include crackles, wheezes, rhonchi, and stridor.
Crackles
Crackles are non-musical, short, explosive sounds that resemble the sound of pulling apart hook-and-loop fasteners. They occur when small airways that were previously collapsed suddenly snap open during inspiration, or when air passes through fluid or secretions.
Wheezes
Wheezes are continuous, musical, high-pitched sounds that resemble a whistling or hissing. They are typically heard when air is forced through narrowed airways. While most often heard during expiration, they can sometimes be present during both phases of the breath cycle.
Rhonchi
Rhonchi are continuous, lower-pitched, coarse sounds likened to snoring or a rumbling noise. These sounds usually originate from the larger airways and are caused by the presence of thick secretions or mucus, which may shift or clear slightly after a cough.
Stridor
Stridor is a distinct, loud, high-pitched, musical sound heard primarily during inspiration. This sound originates from the upper airway, such as the voice box or windpipe, and suggests a significant obstruction in that area. The presence of these sounds indicates the need for further medical evaluation.