Cover HSC Section6_Nov2016-Book.pdf

321 / 412

Phase difference
With relatively larger N G-lateral phase difference, vocal fold vi-
brations in patients with VFA were more asymmetrical than
those of vocally healthy subjects. Left-right difference of
mass, tension, mucoelasticity of the vocal fold resulting from
a different degree of muscular atrophy, and muscular/mucosal
degeneration as well as asymmetry of the laryngeal frame
may play a role here.1,18,19
GAW parameters
The GAW parameters failed to reveal significant intergroup dif-
ferences although NL -minimal glottal area and NL-maximal
glottal area were larger, and glottal area difference index was
smaller in the VFA group as a trend. This result was consistent
with the study of Bloch and Behrman 6 that reported no signif-
icant difference in NL -minimal glottal area between the control
and VFA groups. Larger NL-maximal glottal area found in the
present study may be owing to an increased glottal flow in pa-
tients with VFA (Table 1), and decreased muscular tension of
the vocal fold resulting from the muscular atrophy, leading to
a greater lateral excursion of the vocal folds.18 The smaller
glottal area difference index observed in VFA signifies the
decreased alternating current of glottal flow, the glottal flow ef-
ficiency in other words.
Glottal gap
The result that 30% of elderly vocally healthy subjects had a
glottal gap in the present study was consistent with the findings
in the literature: Pontes et al 10 reported that the incidence of
glottal gap in normal elderly population was 58%, for instance.
Strictly speaking, the vocally healthy subjects with a glottal
gap in the present study (as well as those in the study of Pontes
et al,10 perhaps) should be termed as ‘‘pathological but asymp-
tomatic’’ rather than ‘‘normal,’’ though. Because the prepon-
derant glottal gap was different between the control
(anterior) and VFA groups (spindle shaped), the location of
the glottal gap may serve as a clue to differentiate VFA from
normal aging.
Glottal outlet
No significant intergroup difference of NL -glottal outlet in the
present study was a contradictory result to the report by Bloch
and Behrman, 6 who reported significantly smaller NL-glottal
outlet in the VFA group than the normal group. One possible
explanation is an interindividual difference of a maladaptive
supraglottal hyperactivity as a compensatory strategy for
incomplete or decreased glottal closure. 6 Another possible
explanation is the posterior displacement of the petiole of
epiglottis associated with a descension of the larynx observed
in a male low-pitch phonation, 17 or an elevated laryngeal posi-
tion observed in high-pitch phonation. 22
Limitations
Overall, the combination of multiple HSDI analysis methods
adopted in the present study was effective in the objective docu-
mentation of vocal fold vibrations in VFA. Applying the same
technique to the evaluation of other laryngeal pathology (eg,
vocal fold scar or sulcus vocalis) will be called for in the near
future to further validate its utility.
The study design in which the HSDI study and acoustic or
aerodynamic studies were performed on separate occasions
may be a limitation of the present study, however. Although
the effort was made to make the conditions of examination
equal as much as possible, there could be a minor variation
in F 0 or sound pressure level, leading to relatively low corre-
lations between HSDI parameters and acoustic/aerodynamic
parameters. Another limitation may be the use of a rigid
endoscope for the HSDI recording, which could yield unde-
sirable laryngeal tension during the study. The short time in-
terval for HSDI analysis as well as the relatively limited
subject number (especially of male vocally healthy subjects)
may be other limitations. Furthermore, the heterogeneity in
the VFA group in the present study may have existed,
although the selection of recruited subjects and the diagnosis
was based on the agreement of three or four certified otorhi-
nolaryngologists specializing in vocal treatment: Because the
differential diagnosis among VFA, sulcus vocalis, and vocal
fold scar is not always clear-cut, there is inevitable room for
subjectivity.
In the future study, the improvement of the study design by an
introduction of simultaneous recording system of HSDI and
acoustic signal or aerodynamic data, the introduction of trans-
nasal flexible HSDI, the further refinement of analysis tech-
nique with more automation that allows much extended time
interval for analysis, and the expansion of subject number
will be warranted.
CONCLUSION
The quantitative HSDI analysis of VFA revealed larger open
quotients, lateral phase difference and integral glottal width
(the average glottal width over a glottal cycle), and smaller
speed index than vocally healthy subjects. Gender difference
was noted in lateral phase difference, integral glottal width,
and speed index. Correlation study revealed mild-to-
moderate correlations between HSDI-derived parameters
and conventional acoustic or aerodynamic parameters, and
moderate-to-strong correlation among HSDI parameters.
The combination of multiple HSDI analysis methods was
effective in the objective documentation of vocal fold vibra-
tions in VFA.
Acknowledgments
This research was not funded by any organization or grant.
There was no conflict of interest to be disclosed.
REFERENCES
1.
2.
3.
.
Akihito Yamauchi, et al HSDI Analysis of VFA
96