Mechanisms of dyspnea in healthy subjects

Dyspnea is a general term used to characterize a range of dif- ferent descriptors; it varies in intensity, and is influenced by a wide variety of factors such as cultural expectations and the patient’s experiences. Healthy subjects can experience dysp- nea in different situations, e.g. at high altitude, after breath- holding, during stressful situations that cause anxiety or panic, and more commonly during strenuous exercise. Discussing the mechanisms of dyspnea we need to briefly take into account the physiological mechanisms underlying the sensation of dyspnea: the functional status of the resp- iratory muscles, the role of chemoreceptors and mechanore- ceptors, and how the sense of respiratory motor output reaches a level of conscious awareness. We also need to take into account theories on the pathophysiological mechanisms of the sensation of dyspnea and the possibility that each pathophysiological mechanism produces a distinct quality of breathing discomfort. The terms used by subjects to identify different characteristics of breathing discomfort - dyspnea descriptors - may contribute to understanding the mecha- nisms of dyspnea and providing the rationale for a specific diagnosis.