Breathing is a process that is carried out through the respiratory system, a set of organs that make up the two tracts (Figure 1): the upper (nose, pharynx, larynx), and the lower (trachea, bronchi, and lungs) respiratory tracts. The mechanism of breathing is divided into two phases: inhalation, during which the oxygen of the atmospheric air is taken in, and exhalation, where the carbon dioxide that has accumulated in the human body as a product of cellular metabolism is eliminated. During inhalation, the atmospheric air follows a specific path moving successively from the nose (nasal cavity) to the alveoli of the lungs, and vice versa during exhalation. The alveoli are small grape-like structures inside the lungs that are “surrounded” by a network of small vessels filled with blood, called pulmonary capillaries. Between the wall of the alveoli and the pulmonary capillaries is formed the so-called respiratory membrane, a structure through which this exchange of oxygen with carbon dioxide takes place (Figure 2). Any factor that has the potential to disturb the execution of the above phases, can lead to a disturbance of the normal function of breathing.