[Mechanisms of dyspnea]

Dyspnea has many possible causes and, like pain, is felt in different qualities. Afferent signals originate from the chemoreceptors (pH, O₂ and CO₂) as well as from mechanoreceptors in the lungs, respiratory muscles and thorax. Complexity arises from the fact that both blood gases and the acid-base balance have to be regulated. There is almost always a combination of afferent incoming signals, which can reinforce each other but also determine the quality of the dyspnea experienced. In humans, O₂ is mainly measured peripherally, whereas CO₂ and pH are measured centrally. The areas of the brain involved in regulation are largely located in the brain stem, but cortical areas are also involved in the perception of dyspnea.The majority of patients experience a feeling of air hunger as the main discomfort. Subsequently, this results in emotional processing with the components of anxiety, frustration and fear.