Mechanisms of breathlessness
Jensen D., Pattinson K., Jolley C.
The perception of breathlessness in the sensory (intensity) and affective (unpleasantness) domains involves the integration of respiratory efferent and afferent sensory information within cortical and subcortical neural networks. Recent advances in the visualisation of the neurobiology of breathing and physiological measurement of the neural respiratory drive (NRD) have furthered our understanding of breathlessness through the investigation of: 1) altered pulmonary physiology in symptomatic patients; and 2) the mechanisms of action of established and novel interventions. Irrespective of the underlying pathophysiology, the findings of such studies support the hypothesis that breathlessness intensity in obstructive and restrictive lung disorders reflects the awareness of increased NRD required to support ventilation, consequent to intrinsic respiratory mechanical loading and/or increased ventilatory demand. Qualitatively distinct descriptors of breathlessness (e.g. work/effort, air hunger, unsatisfied inspiration) probably involve the integration of discrete afferent inputs relative to the prevailing level of NRD. Conditioned responses are likely to underlie learned behaviours driving physical activity avoidance and breathlessness-related anticipatory fear and anxiety, contributing to the vicious cycle of functional decline in CRD.