However in order to fully appreciate the mechanism involved in this process an understanding of speech mechanism with respect to the role of vocal fold nodules is required. This is discussed below;
The larynx or the voice box has a twin infolding of mucous membranes (vocal folds) stretched across the larynx. During speech or phonation, the air flow (originating from the lungs) is modulated by these membrane vibrations. Increased air flow/air pressure in the lungs causes the folds to open and once the pressure recedes after the air flows out the fold close again. These folds vibrate when closed due to internal air pressure. (Cumming 2005) In effect, the loudness of speech or what is best termed as the pitch of the voice is determined by resonance frequency of the vocal folds and is measured in hertz. Fundamental frequency of vocal fold vibration correlates with changes in vocal fold tension and subglottal pressure and hence vocal fold mass, stiffness, and viscosityis the main predictor of the pitch of the voice (Hirano 1987).
Vibrations of the vocal folds that are too forceful or prolonged result in vascular congestion. If persistent they will eventually result in hyalinization of superficial lamina propria and eventually this is likely to lead to the formation of nodules.