The aim of the present study was to investigate whether breathing through the nose with a damp gauze for ten minutes improves vocal folds functionality and, as a consequence, mucosal wave and voice quality. For this purpose, participants were recruited and divided into three treatment groups (Gauze group, Control group and Exercise group) and evaluated before (Pre-Test) and after (Post-Test) a group-specific task through laryngostroboscopic examinations, acoustic analysis and perceptual evaluations. Results showed that, after the damp gauze treatment, significant changes occurred concerning vocal fold functionality, mucosal wave quality (the Glottic Closure, the Amplitude of mucosal wave and the Maximum Opening of the Glottic Space), and perceptual and acoustic voice quality (B – Breathiness- of GRBAS scale and shimmer form the MDVP).
Referring to the present results, only after the damp gauze treatment vocal fold functionality and voice quality significantly improved. We attempted to control all variability possible between participants. Thus, we evaluated the inflammatory factors background with an initial self-assessment of vocal well-being, which showed that all treatment groups were homogenous. This suggested that results driven by the treatments could not be influenced by differences between participants because all had similar voice backgrounds (e.g., no elite use of voice, inflammatory factors, etc.), but rather for the treatment itself (49).
Also, in order to improve the effect of water penetration into the mucosa, participants of the Gauze group were asked to emit sounds while breathing through the damp gauze. The movement of the mucosa might increase water penetration into the tissue, just like an ointment needs massage to help its absorption by the skin (30,31). For this reason, the proposed vocal warm-up exercises consisted of ascendingdescending glissandos with the /i/ vowel (favouring a longitudinal stretching of the vocal folds) and very low and high volume sustained /u/ vowels (promoting a transversal vocal folds stretching). However, such modifications are not related to the vocal warm-up exercises (the Exercise groups did not show significant changes after ten minutes performing the same warm-up tasks), but with the combination of both, vocal warm-up exercise and surface hydration.
Thereby, these results suggest that direct surface hydration through damp gauze improve the vocal fold functionality and perceptual and acoustic voice quality. This change was made after ten minutes of using the damp gauze. Previous research explored the benefits of hydrate directly the vocal folds through breathing through the nose with humidifiers (14,15). The task was to breathe normally in a room with a humidifier for a period of 4 hours. Humidifiers are a good solution to hydrate the vocal folds; however, the difference between the damp gauze and the humidifiers resides in the time of administration. Water droplets expelled by the humidifiers are smaller that 10µm, and it is known that droplets of this size fall into the lower respiratory tract rapidly and do not stay in the upper tract long (23,24,50). However, droplets bigger than 10µm remain longer in the upper respiratory tract (23,24,50). Then, it seems, that droplets of the damp gauze may be bigger than 10µm as these may stay longer in the throat and after breathing those droplets for ten minutes. This may suggest the fact that administering bigger droplets may benefit the amount of time required for physiological and perceptual changes.
Other researchers exploring direct hydration used different substances in order to hydrate vocal folds (14). But the majority previously dehydrated the upper respiratory tract in order to observe changes. In this study we do not consider previous dehydration as we seek the benefit of treatment on daily life. But highlighting our rationale of the use of the damp gauze it should be noted that previous research evidenced that nasal breathing increased the humidity of inspired air compared with oral breathing (51). Then, breathing water through the nose with damp gauze might represent an advantageous procedure to provide hydration for vocal folds rapidly and efficiently. Such positive effects could be very helpful for those who use their voice professionally in dry environments; for those who want to maintain an optimal hydration during long travels by plane (where dry and conditioned air normally favors mucosal dryness); and for those who need to put their voice in optimal hydration conditions quickly and effectively before performances (e.g. actors and singers).
Specifically, our results show changes in vocal fold functionality (mucosal wave), perceptual quality (breathiness) and acoustic quality of voice (shimmer and jitter) after using the damp gauze. It could be hypothesized that breathing through a damp gauze promotes water penetration into the vocal fold mucosa, thus changing its viscoelastic properties and promoting improved tissue pliability and mobility (7,9). This effect might be due to the interaction between water molecules and mucosal Glycoaminoglycans (GAGs) (52,53) located in the lamina propria, producing a swelling effect on the superficial layers of the vocal folds. As a consequence, vocal fold mucosa might become more turgid, flexible and elastic (9,11). The effects of these events can be observed through laryngostroboscopy, as the maximum glottic opening is greater, the glottic closure is better and the amplitude of the mucosal wave is higher, as reported in the present study.
Previous research already showed that proper hydration reduces viscosity of the vocal fold mucosa, producing favorable changes in voice quality (i.e., jitter and shimmer) and reducing subglottic pressure (1,2,15,16,54) and our findings seems to be in line with the literature. It is known that higher subglottic pressure is needed to sustain effective phonation in conditions of mucosal dryness. To this respect, thanks to hydration, it seems possible that hydrated vocal folds favor less transglottic airflow leakage and – as a consequence – reduced breathiness. Since laryngostroboscopic parameters used for the present study (Glottic Closure, Amplitude of the Mucosal Wave, Maximum Opening of the Glottic Space) showed significant improvements after breathing through a damp gauze, they may be considered promising indirect indicators for vocal folds surface hydration status.
Some considerations and limitations of the present study should be mentioned. One limitation is represented by the small number of recruited subjects and the lack of medium and long term analysis after hydration procedures. Another not negligible limitation is represented by the lack of direct measures of surface hydration status of the vocal folds. Future research should look for strategies for quantifying surface hydration and observing whether damp gauze hydration benefits by itself or by the combination of both damp gauze breathing and vocal exercises. Also, future research should better understand the role hydration plays for the phonatory system and its short and long term effects on larger populations (including subjects suffering from voice pathologies), as well as direct lubrication techniques and specific effects of vocal folds lubrication.
The present study shows that breathing through the nose wrapped with a damp gauze for ten minutes promotes favorable effects on laryngostroboscopic, perceptual and acoustic voice parameters. Proper hydration of the vocal folds not only favors the production of a better voice, but may also increase the turgidity of the mucosa. Even if surface hydration level was not directly measured, it can be hypothesized that vocal folds surface hydration obtained through the described technique may help reach maximum vocal performance with minimum effort, producing a feeling of vocal wellbeing and a reduction in vocal fatigue.