# Effects of Vertical Glottal Duct Length on Intraglottal Pressures in the Convergent Glottis  
[PERSON]  
1 Shaanxi Engineering Research Center, College of Science, Xijing University, 1 Xijing Road, Xi'an 710123, China; [EMAIL_ADDRESS]. Two laryngeal muscles, the vocalis (VOC) and the cricothyroid (CT) muscles, have a primary influence on the determination of the vertical glottal duct length. Contraction of the VOC muscle tends to increase the vertical glottal duct length, creating a more rectangular glottal shape or medial bulging of the vocal folds [9; 10; 11; 12; 13; 14; 15; 16; 17; 18] associated with the chest voice (or modal register). Contraction of the CT muscles lengthens the vocal folds and thereby reduces the vertical glottal duct length, creating a more convergent glottal shape and typically a higher fundamental frequency. The vertical glottal duct length is shorter in the adult female compared with the adult male [8; 19]. Both [PERSON] and [PERSON] (1959) [20] and [PERSON] (2017) [21] have suggested that the vertical glottal duct length influences the glottal closure pattern and spectral shape of the output acoustics. In addition, [PERSON] (1968) [22] indicated that an increase of the vertical glottal duct length would lead to a large vertical phase difference and result in the glottis remaining closed longer. [PERSON] (2009) [23] indicated that an increased vertical glottal duct length may help to maintain the adotucy position against the subglottal pressure leading to longer glottal closure. [PERSON] (2005) [24] also indicated that increasing vertical glottal duct length and subglottal pressure might be able to increase the aerodynamic forces acting on the vocal folds, further increasing vocal fold adduction, shortening the distance between the two vocal folds, enhancing vocal fold collision, increasing vibratory amplitude, and reducing voiced breathiness. [PERSON] (2016) [25] also suggested that the highest closed quotient (CQ) can be obtained for long vertical glottal duct lengths when the vocal folds are tightly approximated and both the intraglottal and subglottal pressures are relatively low. In addition to influencing the aerodynamic forces acting upon the vocal folds, the vertical length of the glottis is also a determining factor of phonatory threshold pressure (PTP) [6; 24; 26; 27; 28]. [PERSON] (2016) [25] reported that PTP first decreases as the vertical glottal duct length increases from very thin vocal folds to a thickness of 2 mm, and then increases with increasing medial surface thickness. [PERSON] et al. (2014) [29] suggest that the PTPs for divergent glottal angles should be lower than those measured for convergent glottal angles or for the uniform glottis. [PERSON] et al. (1997) [26] also suggest that PTP is lowest for the divergent glottis and highest for the convergent one. Their results suggest that highly convergent or divergent prephonatory glottal geometries are associated with higher phonation threshold pressures and should be carefully avoided during phono-surgery. In the clinic, increasing vertical glottal duct length via greater vocal fold thickness might represent an additional physiologic source of improvement for Parkinsonian vocal impairment and thus may increase vibratory amplitude and reduce vocal breathiness in patients as well as potentially lowering an abnormally high PTP [24]. The vocal fold thickness can be increased by injection of collagen or other substances, a procedure that might increase vibratory amplitude and reduce vocal breathiness, to improve the quality of speech among patients with [PERSON]'s disease [30; 31; 32]. Interestingly, vocal fold thickness may be decreased for chronic hemodialysis patients, who may experience transient post-dialysis hoarseness resulting from dehydration [33]. The change of the vertical glottal duct length should have significant effects on the intraglottal aerodynamic parameters such as intraglottal air pressure distributions and velocity profiles as well as the bulk glottal flow and glottal airflow resistance.