Percussion refers to tapping on a surface to determine the underlying structure. It is similar to a radar or echo detection system. Tapping on the chest wall creates vibrations that are transmitted to the underlying tissue, reflected back, and picked up by the examiner's tactile and auditory senses. The sound heard and the tactile sensation felt depend on the air-tissue ratio. The
Table 13-5 Causes of Changes in Tactile Fremitus Increased Tactile Fremitus
Decreased Tactile Fremitus
Unilateral Pneumothorax Pleural effusion Bronchial obstruction
Atelectasis (incomplete expansion of lung tissue) Bilateral
Chronic obstructive lung disease Chest wall thickening (muscle, fat)
vibrations initiated by percussion of the chest enable the examiner to evaluate the lung tissue to a depth of only 5 to 6 cm, but percussion is valuable because many changes in the air-tissue ratio are readily apparent.
Percussion over a solid organ, such as the liver, produces a dull, low-amplitude, short-duration note without resonance. Percussion over a structure containing air within a tissue, such as the lung, produces a resonant, higher amplitude, lower pitched note. Percussion over a hollow air-containing structure, such as the stomach, produces a tympanic, high-pitched, hollow-quality note. Percussion over a large muscle mass, such as the thigh, produces a flat, high-pitched note.
Normally, in the chest, dullness over the heart and resonance over the lung fields are heard and felt. As the lungs fill with fluid and become more dense, as in pneumonia, resonance is replaced by dullness. The term hyperresonance has been applied to the percussion note obtained from a lung with decreased density, such as that found in emphysema. Hyperresonance is a low-pitched, hollow-quality, sustained resonant note bordering on tympany.
In percussion of the chest, the examiner places the middle finger of one hand firmly against the patient's chest wall, parallel to the ribs in an interspace, with the palm and other fingers held off the chest. The tip of the right middle finger of the other hand strikes a quick, sharp blow to the terminal phalanx of the left finger on the chest wall. The motion of the striking finger should come from the wrist and not from the elbow. Paddleball players use this motion naturally, whereas tennis players must learn to concentrate on using this wrist motion. The technique of percussion is diagrammed in Figure 13-14 and demonstrated in Figure 13-15.
Try percussion on yourself. Percuss over your right lung (resonant), stomach (tympanic), liver (dull), and thigh (flat).
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