[Evaluation of laryngeal sound generation with FFT analysis of glottic impedance in patients with recurrent nerve paralysis].

The electroglottogram (EEG) is known to be related to the motion of vocal folds. The major hypothesis is that the EGG is related to the area of contact of the vocal folds. EGG is thought to be incapable of measuring or monitoring non-contact type vibratory events in the larynx. Recently it was demonstrated by fast Fourier transformation (FFT) analysis of EGG curves that the resulting EGG can be interpreted as a sum of a 'laryngeal fundamental with overtones'. This necessitates a new interpretation of normal EGG waveshape. This study was undertaken to prove the hypothesis that (pathological) EGG curves contain information even about non-contact type vibratory events in the larynx during phonation when analyzed by FFT. Patients with vocal fold paralysis were asked to phonate sustained vowels (/a/, /e/, /i/, /o/, /u/). Voice sounds and EGG signals were recorded simultaneously, routed to a frequency analyzer and subjected to real-time FFT analysis. In all cases original EGG signals would have been classified as pathological. However, in all recordings the laryngeal fundamental frequency and--in some patients--overtones with their intensities could be extracted and compared to harmonics extracted from voice sound. This is the first report of FFT analysis of EGG signals in patients with vocal fold paralysis. It is proposed that vocal folds vibratory events may be of non-contact type and that they can be monitored by analysis of glottic impedance.