Percussion is a fundamental technique used in the physical examination, serving as one of the four main diagnostic methods alongside inspection, palpation, and auscultation. It involves the examiner tapping on a patient’s body surface, typically using a finger placed on the skin. This action generates sound waves and vibrations that travel through underlying tissues.
The primary purpose of percussion is to help the examiner determine the size, consistency, and borders of underlying structures without using invasive methods. By analyzing the sound produced, a healthcare provider can evaluate whether a body cavity is filled with air, fluid, or solid tissue. This non-invasive assessment provides data regarding internal anatomy and potential pathological changes.
The Language of Percussion Sounds
The sounds produced during percussion are classified into five categories, each corresponding to a different density or state of the underlying tissue. The most hollow sound is Tympany, a high-pitched, drum-like tone heard over air-filled cavities like the stomach or intestines. This occurs because gas-filled organs vibrate freely, similar to tapping a taut drum head.
When the examiner percusses over normal lung tissue, the sound is described as Resonance, a low-pitched, hollow tone indicating the presence of air mixed with solid tissue. Hyperresonance is an exaggerated, booming sound, louder and lower-pitched than normal resonance. It suggests an abnormal amount of air, such as when air is trapped within the lungs or the chest cavity.
Dullness is a medium-intensity, muffled, thud-like sound heard over solid organs like the liver or spleen. It indicates that the sound wave is quickly dampened by a solid or fluid-filled structure. Flatness is the softest and highest-pitched sound, heard over extremely dense tissues, such as large muscle masses or bone, where sound transmission is virtually nonexistent.
Assessing the Respiratory System
Percussion is systematically performed over the patient’s chest and back to evaluate the health of the lungs and surrounding pleural spaces. The examiner compares the sounds from one side of the chest to the symmetrical point on the other side to detect differences in air content.
Finding dullness or flatness over a section of the lung suggests that the normally air-filled space has been replaced by something denser. This finding can signify consolidation, where the alveoli are filled with inflammatory fluid and cells (e.g., pneumonia). It may also indicate fluid buildup in the pleural space, a condition known as pleural effusion.
Conversely, hyperresonance over one or both lung fields suggests an excessive amount of air within the chest cavity. This is common in individuals with emphysema, where air is chronically trapped due to damaged lung elasticity. A more acute cause is a pneumothorax, which is free air that has escaped into the pleural space, often causing the lung to collapse.
Diaphragmatic excursion determines the vertical movement of the diaphragm during respiration. The examiner percusses downward until the sound changes from the resonant lung tone to the dullness of the diaphragm. The difference in this border between full inspiration and full expiration measures the patient’s respiratory mobility. A reduced measurement can signal conditions that restrict lung movement, such as paralysis of the diaphragm or severe emphysema.
Mapping Organ Boundaries and Fluid Accumulation
Outside of the respiratory system, percussion is essential for assessing the abdomen and defining internal organ borders. The technique locates solid organs by listening for the transition from the tympanic sounds of gas-filled intestines to the dull sound of a dense structure. For example, the upper border of the liver is determined by percussing down the chest until the sound shifts from lung resonance to liver dullness, while the lower border is found by percussing upward from the abdomen’s tympany.
The size and location of the spleen can be estimated by percussing a specific area on the left side of the body, where the tympany of the stomach gives way to the dullness of the spleen. An abnormally large area of dullness suggests organ enlargement (splenomegaly). Changes in the expected tympanic sound across the abdomen can be significant, as a complete absence of tympany may suggest a large mass or widespread fluid accumulation.
Percussion is effective in identifying abnormal fluid collections, such as ascites (excess fluid in the peritoneal cavity). When a patient with ascites is lying flat, the fluid pools in the flanks, causing a dull sound when those areas are percussed. The air-filled bowel loops float to the top, resulting in tympany near the center of the abdomen.
To confirm the presence of free fluid, the examiner performs the shifting dullness test. By having the patient turn onto their side, the fluid relocates; the area that was previously dull becomes tympanic, while the new dependent area becomes dull. This phenomenon helps distinguish free fluid from a fixed mass. Percussion can also assess the bladder; a full, distended bladder produces a dull sound due to fluid, whereas an empty bladder produces tympany from the overlying bowel.