The Impact of Double Source of Vibration Semioccluded Voice Exercises on Objective and Subjective Outcomes in Subjects with Voice Complaints
Introduction
In the last decades, evidence supporting both the effectiveness and the underlying physiology of semioccluded vocal tract exercises (SOVTEs) has accrued. Consistently, the use of this group of exercises has importantly increased in voice rehabilitation and training contexts. SOVTEs can be divided into two different groups, depending on the number of sources of vibration involved during exercise: (1) SOVTEs with a single source of vibration (vocal folds only, ie, tube phonation with the free end in the air, bilabial consonant /ß:/, hand-over-mouth technique, Y-buzz, and humming) and (2) SOVTEs with a secondary source of vibration added into the vocal tract (water bubbling from the tube phonation with the free end into water, lip trill, tongue trill, and raspberry).
Miller and Schutte proposed that a second source of vibration at the distal part of the vocal tract produces a fluctuating oral pressure (Poral) impacting on vocal fold vibration.1 The effect of a secondary source of vibration has also been attributed to a vibration of vocal tract tissues.2 The fluctuating Poral during this type of exercises has been reported to cause a “massage-like effect” in vocal folds and the vocal tract3 with reduction of muscle tension, especially in subjects diagnosed with laryngeal and pharyngeal hyperfunctionality. This massage-like effect could increase blood flow in vocal folds. Nevertheless, this hypothesis is not based on data collected within the voice field but on evidence from sports medicine.4, 5, 6
Previous research has established the presence of Poral modulation during water bubbling at a frequency of 15–40 Hz.7, 8, 9, 10 The magnitude of variation of Poral during tube phonation in water has also been explored. An in vivo study by Radolf et al10 showed about two to four times higher peak-to-peak variation in Poral with the tube immersed 10 cm in water, compared with phonation on [u:]. Similarly, in a modeling study by Horáček et al,7 phonation at conversational loudness resulted in 2.2 times larger peak-to-peak pressure variation and 1.6 times larger glottal amplitude variation with the tube submerged 10 cm in water, compared with phonation on [u:]. These results suggest that the modulation of Poral water bubbling could have an effect on vocal fold oscillation and possibly on vocal fold and pharyngeal tissues. Although no studies have been carried out to explore the fluctuation of Poral during other SOVTEs with a secondary source of vibration (eg, tongue and lip trills), they may have a comparable effect because of tongue and lip vibration.
The effect of a secondary source of vibration on vocal fold pattern was reported by Andrade et al11 in an electroglottographic (EGG) study performed with different SOVTEs. Results showed that SOVTEs with a secondary source of vibration (lip trills, tongue trills, and water bubbling) presented a significantly greater range of EGG contact quotient (CQr) and range of fundamental frequency (F0r) than the baseline condition. A higher CQr is an indicator of greater variability of open and closed phases of the vocal fold vibration. A higher CQr is an indicator of greater variability of open and closed phases of the vocal fold vibration. A higher F0r indicates greater variability of the vocal fold vibration frequencies. No changes were observed for the same variables when phonating a single source of vibration SOVTEs (humming, hand over mouth, and straw phonation). Authors labeled these two groups of SOVTEs as “fluctuating” and “steady.”11 They also suggest that exercises with a secondary source of vibration could produce a stronger massage effect because of a larger variability in CQr caused by changes in Poral. Therefore, a secondary source of vibration exercises may be better suited for patients with excessive tension of laryngeal and pharyngeal muscles than SOVTEs in a “steady” group.
Enflo et al8 showed that the modulation of Poral during water bubbling affects phonation. They observed that when Poral increases, there is a reduction on the amplitudes of both audio and dEGG signals. When Poral decreases (the moment of bubble release) the opposite occurs. A recent high-speed imaging study by Granqvist et al12 reported that vocal fold vibration and EGG signal were affected by Poral variation when the tube was submerged in water.
Even though evidence has shown physiological effects of a double source of vibration SOVTEs on air pressure, audio, EGG, and glottal variables, to date there are no data supporting the hypothesis of a massage-like sensation on the vocal folds or vocal tract produced by different SOVTEs with a secondary source of vibration. Moreover, no data related to the effects on objective parameters of this group of exercises has been published. The purpose of the present study was to observe the possible effect of a double source of vibration SOVTEs on subjective and objective variables in subjects with voice complaints. Possible differential effects produced by these voice exercises were also inspected.
Based on previous data and clinical reports, we hypothesized that (1) all double sources of vibration SOVTEs should produce a reduction in the sensation of muscle tension, an increase in the ease of voice production, and a reduction in sensory discomfort in the throat (as indicators of a possible massage-like effect); (2) some objective variables (eg, CQEGG, overall sound pressure level [SPL], glottal airflow rate, subglottic pressure (Psub), phonation threshold pressure [PTP]) should vary to reflect a more economic voice production (high acoustic output and low vocal fold impact stress); and (3) based on clinical reports, some exercises might generate a greater improvement than others.
Section snippets
Participants
Eighty-four participants were initially enrolled in this study. All participants were randomly assigned to one of four balanced treatment groups (n = 21): (1) water resistance therapy; (2) tongue trills; (3) lip trills; and (4) raspberry (tongue and lip trills at the same time). A simple randomization method was used. When arriving to laboratory, subjects had to blindly choose one of four cards containing the name of the treatment to be applied in that particular session. When someone was
Sustained speaking vowel [a:] task's variables
Figure 1 plots means for sustained speaking vowel [a:] task's variables. Significant ANOVA test results were found only for the interaction term on glottal airflow (F = 251, P = 0.028, GES = 0.03). The interaction's significance is driven by the contrast Pre against Post 2 on the raspberry exercise (b = −0.03, z = −2.68, P = 0.02) and Post 1 against Post 2 on tongue trills (b = 0.04, z = 3.19, P = 0.003). As for the remaining variables, only on the CQ was there another significant paired
Discussion
The present study assessed the effects of a double source of vibration SOVTEs on subjective and objective variables in subjects with voice complaints. Results seem to support the role of this group of voice exercises as a potentially effective tool for reducing symptoms of vocal tract discomfort (eg, sensation of muscle tension in laryngeal and pharyngeal areas). Observed effects for subjective variables were more manifest than effects for objective variables. Although some significant changes
Conclusion
SOVTEs with a secondary source of vibration may reduce symptoms related to throat physical discomfort in subjects with voice complaints. They may also contribute to an improved self-perceived resonant voice quality and a reduction in the sensation of muscle tension. These changes could be associated with the so-called massage-like effect attributed to this type of SOVTE. Water resistance therapy and raspberry seem to produce the greatest effects. Changes occur immediately after exercises and
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