Experimental study on level difference between left and right vocal folds

Abstract

IntroductionIt has been known that asymmetry between left and right vocal folds, induced, e.g., by vocal cord nodules, polyps, and vocal cord atrophy, is one of the leading causes of voice disorders. The asymmetric configuration may lead to incomplete glottal closure and results in a variety of voice instabilities such as subharmonics, biphonation, and chaos. Careful examinations are needed to investigate the effect of asymmetry on the voice production. The preceding studies mainly focused on asymmetry with respect to tension imbalance and geometrical difference between the left and right vocal folds. It has been known, however, that the level difference, that is defined as the distance between the upper surfaces of the bilateral vocal folds in the inferior-superior direction, is also a typical result of atrophy of the paralyzed vocal fold. Kadota and Yumoto [9] measured the level difference of patients with unilateral recurrent laryngeal nerve paralysis using a computed radiography system and reported that the level difference provides a good index for the quantitative assessment of the effectiveness of phonosurgical treatment. Hong and Jung [10] also reported a variety of level differences between paralyzed and normal vocal folds for patients with unilateral vocal fold paralysis.Although the level difference between the left and right vocal folds may have an influence on laryngeal functions, its effect on voice production has not yet been thoroughly investigated. The aim of the present letter is to utilize three types of physical models of the vocal folds to study the effect of the level difference on the vocal folds vibration. We measure the phonation threshold pressure as a primary index for quantifying the difficulty in phonation. Our experiments reveal that the phonation threshold pressure increases signifi-

Imaging of auto-oscillating vocal folds replicas with left–right level difference due to angular asymmetry

“…2. Experiments were performed using three different (M5, MRI and EPI) deformable multi-layer silicone VF replicas [11,12,13,14,15] depicted in Fig. 1 [10,16].…”

Influence of level difference due to vocal folds angular asymmetry on auto-oscillating replicas

“…In order to compensate the reduced movement of the paralyzed VF, the position of the normal VF in the inferior-superior direction is changed. Consequently, a vertical level difference between the left and right VF emerges, where the paralyzed VF is often inclined in the sagittal plane (right VF in in literature [3][4][5] . Quantitative characterization of this spatial asymmetry from imaging on human subjects is extremely tedious [1][2][3] .…”

“…Recently 4,5 , the impact of level difference between parallelly located VFs, hereafter referred to as parallel level difference, was investigated. The preceding study, however, did not take into account inclination of the paralyzed VF, which is physiologically more close to reality.…”

Low-strain effective Young’s modulus model and validation for multi-layer vocal fold-based silicone specimens with inclusions

“…The validation was done on 13 bone-shaped molded silicone specimens containing two (⊥ or ) or three (⊥, or ⊥ ) layers and E e f f ≤ 40 kPa. The Young's modulus E of the molded layers was varied considering two different silicone mixtures (Thinner-Ecoflex (TE) or Thinner-Dragonskin (TD)) at different mass mixing I [10][11][12][13][14][15][16][17][18] . The measured Young's modulus E of molded layers varies between 4 kPa and 65 kPa, which corresponds to the range associated with anatomical layers in a normal adult male human vocal fold [19][20][21][22][23][24][25] .…”