Mechanisms of Dyspnea

Although the mechanisms of dyspnea are poorly understood, new scanning technologies allow the imaging of brain function under different activities and stimuli so that researchers can visualize the areas of the brain that are activated when dyspnea is perceived.

Dyspnea is not a localized sensation, such as touch or pain, but a vague visceral sensation more akin to hunger or nausea. Such sensations are dependent on centrally generated neural activity. Research has shown that the sensation of dyspnea is perceived in the primary sensory cortex, while the feeling of an urge to breathe activates a region of the insular cortex, a part of the limbic structures of the brain that are associated with other visceral sensations.

Current studies show that the stimulation of ventilation is necessary for dyspnea to occur. Little or no dyspnea has been experienced with increases in ventilation provided by an external source (such as an iron lung), or as a result of voluntary hyperventilation. Perception of the sensation is apparently dependent upon the degree to which respiratory-related neurons in the brain stem are stimulated. Stimulation of ventilation by exercise, hypoxemia, hypercapnia, and an abnormal increase in the acidity of body fluids all induce dyspnea.

This connection between stimulation of ventilation and dyspnea is not always maintained, and can be altered by other factors, such as altitude or comorbidities. Figure 1A, below, illustrates the current understanding of dyspnea. Hopefully, more research will yield further information on the mechanisms of dyspnea, and the role other forces (such as emotions) play in the sensation