Effects of Laryngeal Vibratory Asymmetry and Neuromuscular Compensation on Voice Quality

Abstract

Introduction: Vibratory asymmetry and neuromuscular compensation are often seen in laryngeal neuromuscular pathology. However, the ramifications of these findings on voice quality are unclear. This study investigated the effects of varying levels of vibratory asymmetry and neuromuscular compensation on cepstral peak prominence (CPP), an analog of voice quality.Study Design: In vivo canine phonation model. Methods: Varying degrees of vocal fold vibratory asymmetry were achieved by stimulating one recurrent laryngeal nerve (RLN) over 11 levels from threshold to maximal muscle activation. For each of these levels, phonation was induced at systematically varied combinations of neuromuscular compensation: three levels each of contralateral RLN stimulation (80%, 90%, and 100% of maximal), superior laryngeal nerve (SLN) activation (0%, 50%, and 100% of maximal), and airflow levels (500, 700, and 900 mL/s). Vocal fold symmetry was determined by assessing the opening phase of the vibratory cycle in highspeed video recordings. Voice quality was estimated acoustically by calculating CPP for each voice sample.Results: Eight hundred twenty-two phonatory conditions with varying degrees of vibratory asymmetry were evaluated. CPP was highest at vibratory symmetry. Increasing levels of asymmetry resulted in significant decreases in CPP. CPP increased significantly with increasing contralateral RLN activation. CPP was significantly higher at 50% SLN activation than 0% or 100% SLN activation.Conclusion: Voice quality, as approximated by CPP, is best at vibratory symmetry and deteriorates with increasing degrees of asymmetry. Voice quality may be improved with neuromuscular compensation by increased adduction of the contralateral vocal fold or increased vocal fold tension at mid-levels of SLN activation.

Effects of Thyroarytenoid Activation Induced Vibratory Asymmetry on Voice Acoustics and Perception

“…To validate quantification measures, results must be related to perception of voice quality to be clinically meaningful. 7,15,30 Our results confirm that CPP is a reliable correlate of perceptual measures of dysphonia, as listeners are most sensitive to changes in CPP among all acoustic metrics measured. Despite the lack of significant correlations found between H1-H2 and RMS energy with degree of asymmetry, these acoustic metrics demonstrate significant relationships with listener preference, and their utility in perceptual evaluation of dysphonia remain important complements to CPP.…”

“…An in vivo canine model with graded nerve stimulation, which is a validated method for a direct manipulation of individual laryngeal muscle stimulation, 1 can offer insights on compensatory neuromuscular rescue of vibratory asymmetry. 15,16 However, no prior studies have examined the role of the individual ILMs responsible for VF asymmetry. Despite its importance in voice production, little is known about their contributions in producing VF asymmetries.…”

“…Finally, manipulating the degree of VF asymmetry was unavailable in many previous studies. An in vivo canine model with graded nerve stimulation, which is a validated method for a direct manipulation of individual laryngeal muscle stimulation, 1 can offer insights on compensatory neuromuscular rescue of vibratory asymmetry 15,16 . However, no prior studies have examined the role of the individual ILMs responsible for VF asymmetry.…”

Aerodynamic Performance and Neuromuscular Control in Patients with Unilateral Vocal Fold Paralysis

“…The CT muscle elongates the vocal fold, stiffens the cover layer, and is primarily regarded as the controller of vocal range and glottal vibration [ 12 , 16 , 17 , 18 , 19 , 24 ]. There is increasing evidence suggesting its role in aerodynamics such as SPL [ 20 ], phonation onset pressure, phonation onset flow [ 12 , 24 ], and vocal efficiency [ 30 ], and its effects on aerodynamics may be further influenced by the activation level of TA-LCA and prephonatory VF posture.…”

“…The exclusion criteria were prior history of vocal fold paralysis, not cooperating with or refusing LEMG assessments, history of interventions to paralyzed vocal folds (such as laryngoplasty, intracordal injection, or laryngeal framework surgery), normal findings in TA-LCA from LEMG, or concurrent involvement of the CT muscle. Specifically, patients with abnormal findings in CT muscle were excluded because it has been shown that CT muscle involvement alone is an important factor in determining voice frequency [ 16 , 17 ], voice quality [ 18 ], and aerodynamic performance [ 12 , 19 ]. The study was approved by the Institutional Review Board of Chang Gung Medical Foundation, and informed consent was obtained from each participant before recruitment.…”