Klaske van Sluis

Objective and subjective voice outcomes: a systematic review 29 Figure 2.2: Left violin plot displaying the distribution of the mean F0 outcomes for sustained vowels in 12 studies [27, 32–35, 38, 40–42, 45, 49, 52] ES n =136, TES n =168, H n =115. Right violin plot displaying the distribution of the mean F0 outcomes for running speech in four studies [33, 34, 40, 49]. ES n =34, TES n =44, H n =35. Abbreviations: ES = esophageal speakers; TES = tracheoesophageal speakers; ELS = electrolarynx speakers; H = healthy speakers; F0 = fundamental frequency; Hz = Hertz. Harmonics to noise ratio Eight studies [27, 32, 33, 35, 38, 41, 44, 52] ( n =240) included Harmonics to Noise Ratio (HNR) outcomes, including one level A study of Shim et al. [32], and seven level B studies [27, 33, 35, 38, 41, 44, 52]. Two studies measured Noise to Harmonics Ratio, which was recalculated to HNR [32, 35]. Higher HNR is reflecting better voice quality. The level A rated study of Shim et al. [32] showed better HNR outcomes for healthy speakers compared to ES. Healthy speech was rated as superior to substitute speech in five studies [27, 32, 33, 38, 44]. Comparison between ES and TES showed superior values for TES (Table 2.3; n =5) [27, 33, 35, 41, 52]. However, none of the studies comparing ES and TES found a significant difference between these substitute voices. This is reflected in the violin plots in Figure 3, depicting the comparable HNR outcomes for TES and ES. Maximum phonation time Eight level B rated studies [35, 37, 38, 40, 41, 45, 49, 52] ( n =262) evaluated Maximum Phonation Time (MPT) by phonation of a vowel /a/ or /i/ (Table 2.3, Figure 3). Longer MPT is indicated as being better. Range of MPT values for all groups of speakers is 0.84sec - 23.87sec ( n =8) [35, 37, 38, 40, 41, 45, 49, 52]. In the group of healthy speakers values for MPT are highest [38, 40, 49]. A significant longer MPT for healthy speakers is found in comparison with TES [38]. Within the comparison of the speech rehabilitation groups six studies [35, 37, 41, 45, 49, 52] found that TES has a longer MPT than ES, significant in one study [52].