Introduction

The human larynx has the same essential functions found in the higher evolved species, namely: air conduction, lower airway protection and efforts supporting. To these functions, sound emissions may be added that allows innate communication between members of the same species. Cat meows, dog barks, horse neighs etc., with instinctive variations important for survival.
The human species, this sound function acquires peculiar characteristics in line with cognition development and is called voice. Thus, voice is the sound production resulting from the association of sounds generated by the vocal folds’ vibration with constrictions of the supraglottic cavities molding the expiratory airflow and modified by resonance effects. It is the acoustic support for social communication.
The voice depends of four characteristic dimensions:

• Biological
• Psychological
• Socio-educational
• Axiological – connected with life-values.

If the vocal product of these dimensions are adequate, we have euphony that may be defined as a harmonious association between the elements involved in vocal emission resulting in pleasant sounds produced without difficulties or distress by the speaker and which modifies according the communication situation and context.

Situations where euphony is not sustained may occur causing a condition called dysphonia. Dysphonia may be defined as any difficulty in vocal emission that hinders natural and harmonious voice production. Thus, dysphonia is not a symptom; it is the loss of euphony that may manifest by several symptoms and signs.

There are biological dimension situations where variations, lesions or dysfunctions do not affect vocal emission within certain limits and in these cases we say that the voice is adapted despite organic or functional maladaptation of the structures. Adaptation may fail when other vocal demands occur.

Two different causes may lead to dysphonia: one results from the process of phonatory action and the other is independent of this process, but manifests through it. The first is called functional, it is the function that causes the damage, and the second is organic or symptomatic and denotes the presence of an illness. In functional dysphonia the phonatory process may result in structural damage and when they are detected, the dysphonia is said organic-functional, it means that the lesions are consequent to phonatory traumatic action.