Studying human vocal fold vibration with digital kymography
Visualization of the glottis and vocal folds (VF) vibration is crucial to accurate diagnosis of VF pathologies. Simple endoscopy is commonly used to look for obvious structural abnormalities and stroboscopy is used to analyze VF movement during phonation. However, stroboscopy, as a frequency-dependent method, masks aperiodic vibration, a key characteristic of many laryngeal disorders. High-speed digital imaging is better suited for pathologies that cause aperiodic vibration, but it collects a large volume of data, requires expensive, specialized equipment, and is time-consuming to analyze. Digital videokymography extracts data from a single pixel line in the high-speed video and concatenates the images into a kymogram showing VF vibration at that point over time. It is an efficient and sensitive method of obtaining information about parameters quantifying VF vibration, including amplitude, periodicity, and left-right and anterior-posterior asymmetry. Recently, multiline digital videokymography was investigated as a diagnostic tool for distinguishing vibrational pathologies by using kymograms of pixel lines at different points. Nodules and polyps, which are difficult to differentiate using simple endoscopy or stroboscopy, can be distinguished via kymogram based on the lateral phase difference at 25% of the VF from the anterior commissure; polyps show larger lateral phase asymmetry than nodules. Therefore, multiline digital videokymography can prove a useful clinical tool in cases of aperiodic VF vibration.