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

Abstract

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.

FIG. 1.

Fundamental frequency (F0) as a function of vocal fold strain in (a) the 320 distinct laryngeal neuromuscular activation conditions. The chest-like (green) and a falsetto-like (red) registers are shown and vertical blue lines indicate conditions where phonation onset was not reached at the airflow levels used. F0 versus strain data points are separated by TA activation levels 0–4 in subplots (b)–(f).

FIG. 2.

Fundamental frequency (F0) as a function of glottal distance at the vocal processes (D_vp). The falsetto-like register (red) is grouped closer to the lower D_vp values, compared to the chest-like register (green). Vertical blue lines indicate conditions where phonation onset was not reached at the airflow levels used.

FIG. 3.

The interaction between strain and glottal distance (D_vp) for fundamental frequency (F0). The highest frequencies generally cluster around the high strain, low D_vp region. Starred symbols indicate conditions where phonation onset was not reached at the airflow levels used.

FIG. 4.

Fundamental frequency (F0) as a function of subglottic pressure (ps) reveals that the same F0 can be achieved with a wide range of subglottic pressure. TA activation levels are shown for the falsetto-like F0 cluster.

FIG. 5.

(Color online) Representative muscle activation plots for glottal distance between vocal processes (D_vp) at phonation onset as a function of graded activation of (a) CT versus TA at LCA/IA level 5, (b) CT versus LCA/IA at TA level 0, (c) CT versus LCA/IA at TA level 1, and (d) CT versus LCA/IA at TA level 2. D_vp was calculated as a percentage of glottal width at the baseline non-stimulated resting condition.

FIG. 6.

(Color online) Representative muscle activation plots for vocal fold strain at phonation onset as a function of graded activation of (a) CT versus LCA/IA at TA level 2, (b) CT versus LCA/IA at TA level 4, (c) CT versus TA at LCA/IA level 5, and (d) CT versus TA at LCA/IA level 7.

FIG. 7.

(Color online) Representative muscle activation plots for fundamental frequency (F0) at phonation onset as a function of graded activation of CT versus LCA/IA at (a) TA level 1, (b) TA level 2, (c) TA level 3, and (d) TA level 4. Missing data points (blank areas) in subplot (a) represent activation conditions where phonation onset was not reached at the airflow levels used (300–1600 ml/s).

FIG. 8.

(Color online) Representative muscle activation plots for fundamental frequency (F0) at phonation onset as a function of graded activation of CT versus TA at (a) LCA/IA level 1, (b) LCA/IA level 3, (c) LCA/IA level 5, and (d) LCA/IA level 7. Missing data points (blank areas) represent activation condition where phonation onset was not reached at the airflow levels used (300–1600 ml/s).

FIG. 9.

(Color online) Representative muscle activation plots for phonation onset pressure (P_th) as a function of graded activation of (a) CT versus LCA/IA at TA level 1, (b) CT versus LCA/IA at TA level 3, (c) CT versus TA at LCA/IA level 3, and (d) CT versus TA at LCA/IA level 5.

FIG. 10.

(Color online) Representative muscle activation plots for phonation onset flow rate (ml/s) as a function of graded activation of (a) CT versus LCA/IA at TA level 1, (b) CT versus LCA/IA at TA level 2, (c) CT versus TA at LCA/IA level 3, and (d) CT versus TA at LCA/IA level 5.