Videostrobokymography
Definition:
Videostrobokymography is a technique used to visualize the vibratory pattern of mucosal edges of vocal folds at selected coronal sections along the longitudinal glottic axis.
History:
It was originally introduced in 1970 as an analytical tool for examination of periodic / aperiodic vibration.
Uses:
1. It is used in quantitative documentation of abnormal vocal fold vibrations in various benign lesions like vocal nodules, polyps, Reinke's oedema and unilateral vocal fold palsy.
2. Analysis of glottal onset and offset
3. evaluation of the microdynamic features of the individual oscillatory cycles of the vocal folds
4. studying vocal tremor
5. imaging the mechanism of coughing
6. evaluation of the velocity of the abductory and adductory movement of the vocal folds
Procedure:
A single coronal selection / slice of vocal fold vibration recorded during stroboscopy is analyzed over specified time scale to produce a 2 dimensional image of vibrating larynx. Normal laryngeal vibration creates a typical rhomboid kymographic pattern. Any aberration from this pattern can be considered abnormal. Videostrobokymography digitalizes recorded stroboscopic laryngeal examination and analyzes them using a proprietary software.
Advantages of this procedure:
It does not require repeated endoscopic examination of larynx and instead allows the user to carefully analyze the video images in order to choose the optimal areas of interest.
Factors to be considered before evaluating kymographic images:
In order to accurately interpret the kymographic images one has to consider the following factors:
1. Position along glottal axis
2. Type of voice produced
Position along glottal axis:
Vibratory pattern of vocal folds is dependent on the position of vocal folds during the time of measurement. Two factors which influence the resultant image include:
Position along glottal axis
Angle with respect to glottal axis
In normal cases the middle portion of the vocal fold is considered to be representative for the vibration pattern of the whole vocal cord. In cases of vocal fold lesions the vibratory pattern differ along the glottal axis. This point should be taken into consideration before interpreting images produced.
The angle of the measuring line is, as a standard, adjusted to be perpendicular to the glottal axis.
Type of voice produced:
There are at least three main characteristics of voice which one should take into consideration before interpreting these images:
Phonation pitch
Phonation loudness
Phonation type / voice register
