Influence and interactions of laryngeal adductors and cricothyroid muscles on fundamental frequency and glottal posture control.

The interactions of the intrinsic laryngeal muscles (ILMs) in controlling fundamental frequency (F0) and glottal posture remain unclear. In an in vivo canine model, three sets of intrinsic laryngeal muscles-the thyroarytenoid (TA), cricothyroid (CT), and lateral cricoarytenoid plus interarytenoid (LCA/IA) muscle complex-were independently and accurately stimulated in a graded manner using distal laryngeal nerve stimulation. Graded neuromuscular stimulation was used to independently activate these paired intrinsic laryngeal muscles over a range from threshold to maximal activation, to produce 320 distinct laryngeal phonatory postures. At phonation onset these activation conditions were evaluated in terms of their vocal fold strain, glottal width at the vocal processes, fundamental frequency (F0), subglottic pressure, and airflow. F0 ranged from 69 to 772 Hz and clustered into chest-like and falsetto-like groups. CT activation was always required to raise F0, but could also lower F0 at low TA and LCA/IA activation levels. Increasing TA activation first increased then decreased F0 in all CT and LCA/IA activation conditions. Increasing TA activation also facilitated production of high F0 at a lower onset pressure. Independent control of membranous (TA) and cartilaginous (LCA/IA) glottal closure enabled multiple pathways for F0 control via changes in glottal posture.

Phonatory effects of type I thyroplasty implant shape and depth of medialization in unilateral vocal fold paralysis.

OBJECTIVES/HYPOTHESIS: Medialization thyroplasty (MT) is commonly used to treat glottic insufficiency. In this study, we investigated the phonatory effects of MT implant medialization depth and medial surface shape. METHODS: Recurrent laryngeal nerve (RLN) and vagal paralysis were simulated in an in vivo canine. A type 1 MT was performed using a silicone elastomer implant with variable medialization depths and medial surface shapes: rectangular, V-shaped, divergent, and convergent. The effects on phonation onset flow/pressure relationships and acoustics were measured. RESULTS: Increasing depth of medialization led to improvements in fundamental frequency (F0) range and normalization of the slope of pressure/flow relationship toward baseline activation conditions. The effects of implant medial shape also depended on depth of medialization. Outcome measures were similar among the implants at smaller medialization depths. With large medialization depths and vagal paralysis conditions, the divergent implant maintained pressure/flow relationship closer to baseline. The vagal paralysis conditions also demonstrated decreased fundamental frequency range and worse flow/pressure relationship compared to RLN paralysis. CONCLUSIONS: The depth and medial shape of a medialization laryngoplasty (ML) implant significantly affect both the F0 range and aerodynamic power required for phonation. These effects become more notable with increasing depth of medialization. The study also illustrates that ML is less effective in vagal paralysis compared to RLN paralysis. LEVEL OF EVIDENCE: N/A.

Influence of asymmetric recurrent laryngeal nerve stimulation on vibration, acoustics, and aerodynamics.

OBJECTIVES/HYPOTHESIS: Evaluate the influence of asymmetric recurrent laryngeal nerve (RLN) stimulation on the vibratory phase, acoustics and aerodynamics of phonation. STUDY DESIGN: Basic science study using an in vivo canine model. METHODS: The RLNs were symmetrically and asymmetrically stimulated over eight graded levels to test a range of vocal fold activation conditions from subtle paresis to paralysis. Vibratory phase, fundamental frequency (F0 ), subglottal pressure, and airflow were noted at phonation onset. The evaluations were repeated for three levels of symmetric superior laryngeal nerve (SLN) stimulation. RESULTS: Asymmetric laryngeal adductor activation from asymmetric left-right RLN stimulation led to a consistent pattern of vibratory phase asymmetry, with the more activated vocal fold leading in the opening phase of the glottal cycle and in mucosal wave amplitude. Vibratory amplitude asymmetry was also observed, with more lateral excursion of the glottis of the less activated side. Onset fundamental frequency was higher with asymmetric activation because the two RLNs were synergistic in decreasing F0 , glottal width, and strain. Phonation onset pressure increased and airflow decreased with symmetric RLN activation. CONCLUSION: Asymmetric laryngeal activation from RLN paresis and paralysis has consistent effects on vocal fold vibration, acoustics, and aerodynamics. This information may be useful in diagnosis and management of vocal fold paresis. LEVEL OF EVIDENCE: N/A.

Posterior cricoarytenoid muscle dynamics in canines and humans.

OBJECTIVES/HYPOTHESIS: The posterior cricoarytenoid (PCA) muscle is the sole abductor of the glottis and serves important functions during respiration, phonation, cough, and sniff. The present study examines vocal fold abduction dynamics during PCA muscle activation. STUDY DESIGN: Basic science study using an in vivo canine model and human subjects. METHODS: In four canines and five healthy humans vocal fold abduction time was measured using high-speed video recording. In the canines, PCA muscle activation was achieved using graded stimulation of the PCA nerve branch. The human subjects performed coughing and sniffing tasks. High-speed video and audio signals were concurrently recorded. RESULTS: In the canines, the vocal fold moved posteriorly, laterally, and superiorly during abduction. Average time to reach 10%, 50%, and 90% abduction was 23, 50, and 100 ms with low stimulation; 24, 58, and 129 ms with medium stimulation; and 21, 49, and 117 ms with high-level stimulation, respectively. In the humans, 100% abduction times for coughing and sniffing tasks were 79 and 193 ms, respectively. CONCLUSIONS: The PCA abduction times in canines are within the range in humans. The results also further support the notion that PCA muscles are fully active during cough.

Treatment considerations for early glottic carcinoma: lessons learned and a primer for the general otolaryngologist.

In this commentary, we review our experience with early glottic carcinomas in an attempt to identify points to consider when developing a treatment protocol and technical considerations in oncologic resection to maintain laryngeal function. We highlight several consistent themes: (1) difficult exposure is not always a contraindication to endoscopic resection; (2) depth of invasion may be apparent only intraoperatively; (3) radiation therapy should be offered for deeply invasive cancers requiring extensive cordectomy or for patients who cannot afford lengthy vocal downtime; however, (4) radiation therapy leads to acute dysphagia and collateral damage to the contralateral vocal fold that is avoided with surgery; (5) good voice can be obtained after healing if resection is limited to intramuscular cordectomy; (6) the key to optimal vocal results is adequate glottal closure; and (7) second look operations are occasionally necessary, and therefore preoperative counseling should include this possibility. Since both surgery and radiation therapy achieve excellent oncologic control, a patient-centered approach is preferred in management.

Effects of asymmetric superior laryngeal nerve stimulation on glottic posture, acoustics, vibration.

OBJECTIVES/HYPOTHESIS: Evaluate the effects of asymmetric superior laryngeal nerve stimulation on the vibratory phase, laryngeal posture, and acoustics. STUDY DESIGN: Basic science study using an in vivo canine model. METHODS: The superior laryngeal nerves were symmetrically and asymmetrically stimulated over eight activation levels to mimic laryngeal asymmetries representing various levels of superior laryngeal nerve paresis and paralysis conditions. Glottal posture change, vocal fold speed, and vibration of these 64 distinct laryngeal-activation conditions were evaluated by high speed video and concurrent acoustic and aerodynamic recordings. Assessments were made at phonation onset. RESULTS: Vibratory phase was symmetric in all symmetric activation conditions, but consistent phase asymmetry toward the vocal fold with higher superior laryngeal-nerve activation was observed. Superior laryngeal nerve paresis and paralysis conditions had reduced vocal fold strain and fundamental frequency. Superior laryngeal nerve activation increased vocal fold closure speed, but this effect was more pronounced for the ipsilateral vocal fold. Increasing asymmetry led to aperiodic and chaotic vibration. CONCLUSIONS: This study directly links vocal-fold tension asymmetry with vibratory phase asymmetry, in particular the side with greater tension leads in the opening phase. The clinical observations of vocal fold lag, reduced vocal range, and aperiodic voice in superior laryngeal paresis and paralysis is also supported.