The Larynx And Voice: Examination
The larynx, situated deep in the neck, is relatively inaccessible. Special techniques are therefore required to examine and evaluate its function.
The simplest form of laryngeal examination involves the placement of a small, angled mirror at the back of the throat. This allows the examiner to view the major structures of the larynx. Many finer structures and their movements during normal speech, however, are difficult to discern. In patients with a strong gag reflex, the usefulness of this technique may be limited. Still, this method allows a quick, easy and painless gross examination of the larynx.
Flexible And Rigid Fiberscopic Laryngoscopy
These types of examination use fiberoptic instruments to assist the examiner in visualizing the larynx. The instruments possess a small viewfinder in which the examiner views the image. Typically, the visual output from the instrument is fed via a CCD camera into a video cassette recorder. This allows documentation of a patient's condition and allows for comparison with earlier examinations.
In an examination with a flexible scope, the patient's nasal passages are first decongested and lightly anesthetized. The flexible fiberoptic scope is then threaded through the nose and down the back of the throat into the pharynx. From this position, an image of the larynx and vocal folds (including their movement and position during respiration and speech) can be obtained.
An examination using a rigid telescope involves placement of the tip of the instrument through the mouth into the back of the throat. A prism at the tip allows visualization down into the larynx. This type of exam provides clear and highly magnified images of the vocal cords.
During speech, the vocal folds vibrate far too quickly (more than 100 Hz) to be examined with a normal light source. In order to overcome this, a strobe light is used to illuminate the vocal folds in slow motion. A strobe emits bright pulses of light at evenly spaced intervals. If the frequency of those pulses is the same as the fundamental vibration frequency of the vocal folds, then the folds will appear "frozen" in time. If, however, the frequency of the strobe is slightly less than that of the vocal folds, the folds will appear to move in slow motion.
This type of exam is important because it allows the mucosa of the vocal folds to be examined during voice production. Many disorders of the larynx involve pathologic changes of this tissue. During examination with a regular light source, these changes may go unnoticed. Stroboscopic examination allows easier visualization of any irregularities that may be present.
This type of exam differs from those discussed above in that the larynx is not directly observed. Instead, its function is assessed from the detection of the electrical potential changes that occur in the muscles of the larynx during contraction.
During electromyography, small needles are inserted through the skin into these muscles. Their electrical activity is then recorded on an oscilloscope at rest and during activity (speaking, breathing and swallowing). The pattern, amplitude and duration of the electrical discharge give the examiner clues to the nature of a patient's disorder. For instance, if an electromyograph detects normal electrical activity in a patient with an immobile vocal fold, it would tend to rule out muscular paralysis in favor of some other cause (such as mechanical fixation or joint immobility).
Fluoroscopy is a radiographic technique, similar in principle to an ordinary X-ray, which is used to assess a patient's swallowing function. However, in contrast to the single exposure of a simple radiograph, videofluoroscopy provides a continuous video image. This technique is conducted by a radiologist and speech pathologist. In this exam, the patient ingests mouthfuls of a radio-opaque substance, usually barium, of varying consistencies. As the swallow occurs, the examiner is able to follow the passage of material through the mouth and into the pharynx and esophagus.
A normal swallow includes precisely scheduled transit of the bolus (mass) of barium and characteristic anatomic movements. Any departure from this well-ordered sequence of events may indicate an injury or disease process. Therapeutic strategies can be implemented to enhance the ease and safety of swallowing when abnormalities are observed.