Patterns of brain activity in response to respiratory stimulation in patients with idiopathic hyperventilation (IHV)

Dyspnoea, usually defined as an uncomfortable awareness of breathing, is one of the most frequent and distressing symptoms experienced by patients with lung disease. Idiopathic hyperventilation (IHV) has unknown aetiology and little is known about the mechanisms that cause the characteristic sustained hypocapnia and chronic dyspnoea. We have shown in IHV and other chronic respiratory disorders that air hunger is the dominant sensation during exercise, while resting breathlessness is characterised by an affective component. The increased drive to breathe in IHV, and indeed dyspnoea in all chronic respiratory disorders, might be better understood if the central mechanisms of dyspnoea were known. The aim of the present study was to characterise the cortical processing of respiratory-related sensory inputs in patients with IHV. Four patients with IHV were studied with ethical approval. Respiratory stimulation was produced using transient occlusion of inspiration (TIO) during spontaneous breathing (delivered in early inspiration with duration c. 300 ms; this is well tolerated) while BOLD fMRI was performed on a 3 Tesla Siemens Trio. TIO was associated with significant activation in sensorimotor and pre-motor cortical areas and the cerebellum, notably the anterior insula, an area previously associated with breathlessness in healthy volunteers. These preliminary observations on the pattern of brain activity in response to respiratory stimulation support the hypothesis that breathlessness in IHV may reflect inappropriate cortical processing of respiratory-related sensory inputs.