Objective: Because exhalation causes the vocal cords to passively vibrate, there appears to be some correlation between aerodynamic parameters and various parameters. The present study investigated the relationship between vocal cord vibration parameters and aerodynamic parameters.

Method: Testing was performed on 13 patients with various voice disorders. Observations of the vocal cord vibration were conducted using a high-speed video system (Kay). Subjects were instructed to vocalize the vowel sound /a/ at a comfortable pitch and intensity. The predetermined area was analyzed for 20 cycles. Images taken at a speed of 2000 frames/s were analyzed using Kay Image Processing Software (KIPS). Using the airway interruption method, the phonatory function analyzer PS77E was used to measure sound pressure level (SPL), mean flow rate, expiratory lung pressure, and airway resistance. The present study was approved by the ethics review board and informed consent was obtained. Interrelations among the parameters were investigated by Fisher r-to-Z transformation with the level of significance set at p<0.05.

Results: A correlation existed between SPL and posterior glottal vibration as assessed by kymograph edge analysis (KEA) (left: p=0.0199 and right: p=0.0372) and central glottal vibration (left: p=0.022 and right: p=0.0438). A negative correlation was seen between airway resistance and glottal area waveform (GAW) minimum opening (p=0.0256). A correlation existed between airway resistance and KEA glottal closure (posterior glottis: p=0.003; central glottis: p=0.0377; anterior glottis: p=0.0311).

In most cases vocal changes after operations on the thyroid gland are connected with the trauma of the recurrent laryngeal nerve (RLN) and the external branch of the superior laryngeal nerve (EBSLN). The preservation of the larynx functions can be improved with the use of the intraoperative neuromonitoring.

The vocal function have been assessed among 82 patients after surgical operation on the thyroid gland. 105 RLNs and EBSLNs have been at risk of surgical trauma. During the operation we have been using Neurosine 100 and surgical microscope for RLN and EBSLN identification.  The survey of laryngeal nerve function has been carried out before and after operation. Electromyography (EMG), videolaryngostroboscopy, perceptual analysis of dysphonia and spectrographic voice analysis have been also carried out.

Results: 104 RLNs and 86 EBSLNs have been successfully identified. The vocal changes are typical of 23% of patients   after thyreoidectomy and 12% of patients after hemithyroidectomy.  Unilateral larynx paresis was typical of the 3 patients, 1 patient had the permanent one. These damages have been diagnosed with the use of the standard indirect laryngoscopy.

The 18 patients have had the postoperative changes after the use of EMG of cricothyroid muscle; the 4 patients had the bilateral ones. The postoperative changes of 6 patients have been found out more than 6 months after surgery.

 After videolaryngostroboscopy the damages of the glottis closure at the phonation have been revealed among 7 patients, in 6 months they remained in 5 cases.

The changes connected with the middle voice pitch reduction more then 5% of preoperative size have been found out among 20 patients, after 6 months they have been found out among   7 patients.   

Conclusion: The significant correlation has been found between spectrographic voice analysis and EMG. To our mind, it seems reasonable to assume that the degree of glottis insufficiency caused by the laryngeal nerve damages is associated with the aspirate dysphonia, a low harmonic- noise coefficient, and reduced middle voice pitch.