Percussion is one of the most important techniques of physical examination. Percussion of the chest sets the chest wall and underlying tissues into motion, producing audible sound and palpable vibrations. Percussion helps you establish whether the underlying tissues are air-filled, fluid-filled, or solid. It penetrates only about 5 cm to 7 cm into the chest, however, and therefore will not help you to detect deep-seated lesions.

The technique of percussion can be practiced on any surface. As you practice, listen for changes in percussion notes over different types of materials or different parts of the body. The key points for good technique, described for a right-handed person, are as follows:

■ Hyperextend the middle finger of your left hand, known as the pleximeter finger. Press its distal interphalangeal joint firmly on the surface to be percussed. Avoid surface contact by any other part of the hand, because this dampens out vibrations. Note that the thumb, 2nd, 4th, and 5th fingers are not touching the chest.

■ Position your right forearm quite close to the surface, with the hand cocked upward. The middle finger should be partially flexed, relaxed, and poised to strike.

Pleximeter Finger

■ With a quick sharp but relaxed wrist motion, strike the pleximeter finger with the right middle finger, or plexor finger. Aim at your distal interphalangeal joint. You are trying to transmit vibrations through the bones of this joint to the underlying chest wall.

Strike using the tip of the plexor finger, not the finger pad. Your finger should be almost at right angles to the pleximeter. A short fingernail is recommended to avoid self-injury.

■ Withdraw your striking finger quickly to avoid damping the vibrations you have created.

In summary, the movement is at the wrist. It is directed, brisk yet relaxed, and a bit bouncy.

Plexor Finger

Percussion Notes. With your plexor or tapping finger, use the lightest percussion that produces a clear note. A thick chest wall requires heavier percussion than a thin one. However, if a louder note is needed, apply more pressure with the pleximeter finger (this is more effective for increasing percussion note volume than tapping harder with the plexor finger).

When percussing the lower posterior chest, stand somewhat to the side rather than directly behind the patient. This allows you to place your pleximeter finger more firmly on the chest and your plexor is more effective, making a better percussion note.

When comparing two areas, use the same percussion technique in both areas. Percuss or strike twice in each location. It is easier to detect differences in percussion notes by comparing one area with another than by striking repetitively in one place.

Learn to identify five percussion notes. You can practice four of them on yourself. These notes differ in their basic qualities of sound: intensity, pitch, and duration. Train your ear to distinguish these differences by concentrating on one quality at a time as you percuss first in one location, then in another. Review the table below. Normal lungs are resonant.

Percussion Notes and Their Characteristics

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