Reverse phonation is also called inspiratory phonation, inhaling phonation and inverted phonation2,4–6. From now on, we shall use the term reverse phonation for the present investigation.

Reverse phonation, initially described by Powers, Holtz & Ogura7, by means of a larynx radiologic analysis, caused by the pressure generated above the glottis, through the turbulent air inflow, adducting the vocal folds. During this maneuver, there is a ventricle relaxation and a broadening of the laryngeal vestibule, as well as glottic adduction across the board1–3,8–11, stretching the vocal folds2,9. This maneuver is atypical in the pneumophonic engram used in habitual speech, when there is a voluntary predominance of phonation muscle action and the closure of the glottis observed during regular phonation5,12.

Reverse phonation is related to voice production during air inflow to the lungs. This happens naturally in different situations, including laugh, cry and sighs13. Behlau & Pontes14 consider reverse phonation, whistling, laugh and blowing as the best maneuvers to loose the supraglottic constriction, since they require muscle movements that do not favor vestibular fold approximation.

Lehman8 reports that, during reverse phonation, the vocal folds come together and close the glottis, as it happens during expiratory phonation. During vocal fold adduction, there is an increase in supraglottic pressure, distending the ventricles.

In reverse phonation, the sound comes from the broad and synchronic vibration of the mucosa in the opposite direction, in agreement with gravity. Supraglottic structures are called into action, there is a reduction in median and antero-posterior constriction2,4,7,15.

The vocal fold contact coefficient tends to significantly reduce during reverse phonation when compared to expiratory phonation10,12,16, when there also is an increase in glottic gap9,10.

The findings from Orlikoff, Baken & Kraus10 show that a vocal fold contact coefficient reduction was more significant in men during the utterance of the /a/ vowel. In women, no significant differences were found in the vocal fold contact coefficient12.

During reverse phonation, there is a significant increase in disturbance and contact instability between the vocal folds10,16. This instability was significant in the findings from Kelly & Fisher12, since many participants performed emissions in reverse phonation, similar to the basal sound quality.

The study from Orlikoff, Baken & Kraus10 showed that the quadrangular membrane seemed elongated, and it is speculated that this happens because of a larynx caudal shifting. In the study by Kelly & Fisher12, this elongation seems to be related to the opening in the supraglottic area, which includes the epiglottis anterior movement, which pulls or elongates the quadrangular membrane.

Kelly & Fisher12 also mention an arytenoid compression reduction, which do not come in contact during reverse phonation. This posterior glottis opening, during reverse phonation, is different from the opening that happens during inspiration, when vocal fold adduction varies according to the inspiratory demand9.

The reverse phonation technique helps aphonic patients, or those that develop some atypical form of vocalization, such as ventricular phonation, to activate the true vocal folds vibration. Those individuals that present these alterations for any given time lose their capacity to start vocalization using their true vocal folds2.

The current literature suggests a reduction in ventricular fold action during reverse phonation2,4,10,17,18. These findings come from subjective observations; however, the study from Kelly and Fisher12 seem to prove this statement based on objective measurements.

Behlau et al.6 explain that in cases in which the patient resists a clean utterance from reverse phonation, by means of sustaining a prolonged vowel, regardless of vocal quality, the patient is asked to utter small sound units, as if the patient were panting, with the inspiratory “ihn” and a short expiratory vowel, preferable the “a”, which, generally, the patients reports to be more comfortable, or even “i” or “u”, because tongue elevation in these vowels helps in removing the epiglottis from the larynx lumen.

Reverse phonation is found in babies, in the first minutes of life. The inspiratory cry represents an obstruction in the breathing inspiratory phase and, after this cry, the children need additional air to fill up their lungs and stabilize breathing, which explains the latency between the end of reverse phonation and the later organic breathing. This phenomenon is associated with vocal fold adduction during reverse phonation, which requires a time for them to return to their position on the expiratory phonation onset13.

According to Grau, Robb & Cacace13, both the frequency and duration of the cry in reverse phonation are fundamentally determined by the anatomy of the child's vocal tract, which is made up of cartilage and flexible ligaments. Between four and six months of age, considerable changes start to take place in the child's vocal tract - the larynx descends down the neck. Thus, around six months of age, there is a reduction in episodes of reverse phonation cries.

During reverse phonation, the fundamental frequency increases significantly2,10,12,13,16 when compared to its expiratory counterpart. In average, the reverse phonation is 74 Hz higher16. On the other hand, patients with spasmodic dysphonia have a reduction in fundamental frequency during reverse phonation9.

Reverse phonation has a variable effect when concerning the production of different vowels. The acoustic characteristics of vowels /i, u, a/ produced by women and young men during normal phonation, when compared to the same vowels produced during reverse phonation, reveals a mean fundamental frequency, significantly higher in reverse phonation16.

Significant resonance differences were found in the utterance of vowel /i/ between reverse phonation and normal phonation. In uttering the vowel /u/, the fundamental frequency was considerable higher during reverse phonation. However, in uttering the vowel /a/ in reverse phonation, it was significantly lower. These results show the difference in speech mechanism articulatory control during reverse phonation when compared to normal phonation16.

Intensity does not vary uniformly if we compare reverse phonation emissions with those in the expiratory phase12. The major respiratory effort and the low adduction levels during reverse phonation also result in small intensity changes, if compared. This fact may be explained by the individual strategies used to change from expiratory to reverse phonation12.

The cost-benefit ratio of using reverse phonation in the clinical practice must be carefully analyzed. Although this technique helps in the diagnosis of mass lesions and facilitates vocal production and training, one must take into account the possible risks, such as drying of the vocal tract after long periods of reverse phonation caused by the oral inhalation of air16. Besides drying, its use may cause vocal fold hematoma, if they are mobile19.

During prolonged reverse phonation, patients usually feel that their throats are dry and they need to clear it with one or two coughs in 5 to 10 minute intervals9.

According to Harrison9, there is no inconveniency in the use of reverse phonation during feeding, since there are no episodes of food aspiration described in the literature.

The reverse phonation technique is used in vocal rehabilitation for those cases of psychogenic aphonya, puberphonias, mid-posterior triangular glottic slit, slit by vocal fold paresis or paralysis2,5,6,20,21, phonation with vestibular folds and aryepiglottic phonation2,5,6,22–26. Many authors indicate this technique in the treatment of spasmodic dysfunctions, such an alternative source of phonation, not requiring the use of physiologic phonation, in other words, the expiratory phonation1–6,9,14,27.

The finding from Kelly & Fisher12, in women with normal voices, suggesting a reduction in ventricular fold action during inspiratory phonation supports the use of this technique in the clinical practice. Nonetheless, we still need much research in order to unveil the physiological mechanisms.

The inspiratory sound source is totally supraglottic, with a broad and inverse mucosal movement15. The technique may also be carried out during the utterance of vowels, syllables, words and phrases, performed from the low to the high frequencies and vice-versa, followed by its expiratory phonatory component19.

After learning the reverse phonation technique, the vowel /a/ may be pronounced with pitch variation, and such phonation may be practiced with other vowels, words, phrases, sentences, paragraphs and, during normal conversation26.

Once established, reverse phonation is quickly produced, followed by expiratory phonation. When the pitch of these two types of phonation become equal, the therapist can rest assured that the voice is starting to be produced by the true vocal folds. Little by little, reverse phonation must be eliminated and the voice starts being produced during expiration26.

In the study carried out by Balata28 about a case of psychogenic dysphonia, the inspiratory phonation vocal symptom installed during the phonotherapy. The author thought this vocal manifestation was very curious, the patient started to aspirate her voice, increasing her respiratory and vocal fatigue, making her speech intelligibility even more difficult. In the relevant literature of psychogenic dysphonias we did not find this type of manifestation, in which there was a reverse phonation establishment after its use during the therapeutic intervention.

Added to the use of this technique concerning voice, Kenjo29 reports the use of inspiratory phonation in the treatment of stuttering. After reverse phonation exercises, one may notice fluency improvement during expiratory phonation.

Serafim30 reports that reverse phonation used during larynx assessment allows for a broad understanding of its structure, since the Morgani ventricles and the vestibular folds open up, allowing vocal fold mobilization, with clear glottic exposure, favoring the identification of small lesions, paralysis, among other pathologies. He also adds that in exams performed with expiratory uttering, the larynx is static, since glottis adduction muscles have characteristics which are similar to those of the expiratory muscles, making reverse phonation provide a dynamic study of the larynx, allowing for a more precise diagnosis, and consequently a more proper therapeutic intervention.

The ventricle and the deeper vocal fold layer must be flexible and tumor-free in order to answer to the different pressures developed during reverse phonation. When the ventricles and the supraglottis relax, vocal fold tumors may be ruled out. Reverse phonation is useful in the diagnosis of tumors in the piriform sinuses and the Morgani ventricles, since these structures relax and reveal tumors therein8.

Reverse phonation's greatest contribution, together with larynx endoscopy, to otorhinolaryngological diagnosis is the possibility of better defining the location of these lesions on the lamina propria layers, as is the case with cysts, which may be in superficial layers or strongly adhered to the lamina propria deeper layers31.

As previously mentioned, video-stroboscopy may give us precise information on the dynamic properties of benign larynx lesions. However, clinical experience tells us that larynx endoscopy, with or without stroboscopy, does not reliably tell us about the presence or the size of Reinke edemas. Thus, we suggest forced inspiration maneuvers during endoscopy in order to have a more precise and reliable diagnosis32.

It is clear that reverse phonation benefits patients with spasmodic dysphonia because of the psychological and acoustic voice changes it produces12,16. There is an improvement in speech fluency and intelligibility, and less discomfort during reverse phonation if compared to expiratory phonation9.

Despite the use of reverse phonation by individuals with spasmodic dysphonia in noisy environments be impaired, in noise-free environments, at the telephone or with the use of amplification in amphitheatre, reverse phonation is normal, fluent, and seems to be accepted by listeners, despite voice harshness9.

In general, difficulties are not found during long periods of reverse phonation, except when the individual is exposed to stress, nervousness or restricted time during speeches. Usually, these individuals have difficulties in coordinating speech and breathing. However, with time, the patient ends up developing strategies to compensate for these difficulties9.

Phonation using continuous, low pressure sounds, such as vowels, is easier to be produced in reverse phonation than the production of fricatives, of higher pressure, because of that it may be considered as a starting point for reverse phonation production33. They are also not difficult to be produced during reverse phonation, in an initial position, blunt explosive phonemes, such as /p/, for example. In these cases, the individual makes compensations in order to improve speech intelligibility, but is unable to fully compensate for these difficulties, making the listener to take into account the context and contrast in order to enhance understanding9.

Learning reverse phonation seems to require a change in diaphragm, abdominal and intercostals muscle control, as well as laryngeal muscle control. Learning this control does not seem to be difficult and may be carried out through exercises9.