Percussion of the lungs is a basic, non-invasive part of the physical examination used to assess the density of tissues beneath the chest wall. It involves tapping a finger against the chest to generate a sound wave, which the examiner interprets. This technique helps differentiate between air-filled, fluid-filled, or solid structures within the thoracic cavity. Assessing the quality of the resulting sound helps detect changes in the underlying lung parenchyma and pleural space. Percussion complements other examination methods like inspection, palpation, and auscultation to form a complete clinical picture.
The Purpose of Chest Percussion
Percussion maps organ boundaries and identifies abnormal shifts in tissue density that cannot be observed visually. The sound generated travels through the chest wall and is transmitted differently based on the composition of the underlying lung tissue. Since healthy lung tissue is approximately 99% air, it typically produces a low-pitched, hollow sound when percussed.
When lung tissue is filled with fluid or becomes consolidated (e.g., pneumonia or a tumor), the sound wave is attenuated more rapidly. Similarly, fluid accumulation in the pleural space (pleural effusion) results in a distinct change in sound quality. By systematically percussing the chest from top to bottom and side to side, the examiner compares the sound over one lung field to the corresponding area on the opposite side. This comparison detects subtle changes in density, helping define the size and precise location of an abnormality.
Step-by-Step Guide to Indirect Percussion Technique
The standard method for assessing the lungs is indirect, or mediate, percussion, requiring the use of both hands to generate the sound. The patient should be positioned comfortably, typically sitting upright with arms crossed in front of them to move the scapulae away from the posterior chest wall. This positioning exposes the maximum lung surface for examination.
The middle finger of the non-dominant hand acts as the pleximeter finger, placed firmly against the chest wall. Only the distal phalanx—the fingertip—should be in contact with the skin, usually positioned parallel to the ribs within an intercostal space. Pressure must be applied to ensure the pleximeter finger is securely seated against the tissue, effectively transmitting the vibration.
The striking finger, known as the plexor, is the middle finger of the dominant hand, held in a flexed position. The plexor strikes the distal interphalangeal joint of the pleximeter finger using a quick, sharp, and controlled motion originating primarily from the wrist. This wrist action, similar to that of a drummer, allows the force to be delivered consistently.
The plexor finger must be immediately lifted after the strike to prevent dampening the resulting sound wave and allow it to resonate clearly. Each area should be percussed two to three times to confirm the sound before moving. The examination proceeds in a systematic, ladder-like pattern, starting from the apices and moving downward, alternating between the left and right sides for direct comparison.
Interpreting the Distinct Percussion Sounds
The sounds generated during percussion are categorized based on their pitch, intensity, and duration, each indicating a different underlying tissue density. The sound heard over healthy, air-filled lung tissue is called resonance, characterized by a low pitch and a hollow quality. Resonance is the expected finding throughout most of the lung fields and indicates normal aeration.
When the lung tissue is consolidated or the pleural space contains fluid, the percussion note becomes dull or flat. Dullness is a medium-to-high-pitched sound with a muffled quality and short duration, similar to tapping over a solid organ like the liver. This finding suggests the presence of increased density, such as that caused by a lobar pneumonia, a large tumor, or a pleural effusion, where air has been replaced by more solid or liquid material.
An abnormally loud, low-pitched, and booming sound is described as hyperresonance. This sound has a longer duration than normal resonance and suggests excessive air within the chest cavity. Hyperresonance may be found in conditions causing air trapping, such as emphysema, or in cases of pneumothorax, where air has escaped into the pleural space. Differentiating these distinct sounds provides valuable information about the air-to-tissue ratio within the lungs.