Fiberoptic Imaging Rationale

Fiberoptic imaging can be performed in place of indirect laryngoscopy for detection of vocal cord paralysis. In clinical research, fiberoptic imaging is used to evaluate the mechanical effects of laryngeal and pharyngeal muscle activation on upper airway size. Fiberoptic imaging has also been used in research laboratories to assess upper airway mechanics in the absence of upper airway muscle activity (35, 36).

Methodology

Fiberoptic imaging is an invasive procedure that provides direct visualization of the upper airway. However, it is easily performed in the awake adult patient and is associated with very little discomfort. After topical anesthesia of one nasal passage, the fiberoptic scope is advanced through the nares and along the floor of the nasal passage into the pharyngeal airway. Depending on the outer diameter of the scope, prior application of a nasal decongestant may be of benefit. The glottic aperture is easily visualized from the hypopharynx. No attempt should be made to touch or pass through the unanes-thetized glottis during this visual examination.

Equipment

Application as a diagnostic technique requires a fiberoptic na-sopharyngoscope, optimally with an outer diameter of 4 mm or less, attached to a light source. Physicians performing the procedure should be specially trained in this technique.

When using fiberoptic imaging as a research technique to quantify changes in upper airway dimensions, it is necessary to have a camera attached to the fiberoptic scope to obtain videotape recordings. Individual frames of the videotape can then be analyzed offline, ideally with a personal computer frame grabber and digitizing software. Methods have been described to calibrate the measurements in metric units (36, 37).

Advantages

Compared with indirect laryngoscopy, fiberoptic examination of the upper airway allows a more thorough examination of the upper airway. If a video camera is available, the physical findings can be documented on videotape. This technique is used for clinical diagnostic purposes.

Disadvantages

The fiberoptic equipment is expensive. Standardized techniques should be instituted to sterilize the scope between procedures. Passage of the fiberoptic scope may be associated with a vasovagal reaction associated with hypotension and loss of consciousness. Adequate supportive care should be available in the event of this complication.

Use of fiberoptic imaging of the upper airway in clinical research is laborious even with computer-assisted analysis. In addition to difficulties with calibration of measurements in metric units, the lack of depth perception on the videotape images makes it particularly difficult to detect the edge of the pharyngeal airway that should be measured. Movement and clouding of the scope are other technical difficulties frequently encountered during research studies.

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