[The different types of dyspnoea].

Dyspnoea can be classified into four types with each arising by means of a different mechanism. Air hunger originates from chemoreflex activity. It is inhibited by pulmonary inflation, probably through a reflex induced by stretch receptors in the large airways. The feeling of increased work of breathing particularly occurs during volitional breathing and is augmented by every cause of increased work of breathing or muscle weakness. This feeling is probably induced by activity of the cerebral motor cortex. Tightness of the chest can be due to bronchospasm. This feeling possibly arises from stimulation of 'slowly adapting receptors' in the large airways, which are closely connected to smooth muscle cells. There are indications that tachypnoea can result from the stimulation of pulmonary C fibres. Possible stimuli are pulmonary venous congestion and the intravenous administration of adenosine. Recognizing and understanding the different types of dyspnoea is relevant to the interpretation and treatment of this symptom.