The Physiological Basis of Respiratory Sensation

Respiratory sensation often occurs in patients suffering from acute or chronic respiratory and/or cardiac diseases, leading to dyspnoea. It is supported by the cortical integration of sensory pathways arising from the airways and lungs, respiratory muscles, and circulatory system. Their activation by direct electrical stimulation or circumstances mimicking pathological events (mechanical and less often chemical test agents) evokes cortical potentials and modifies the spontaneous EEG rhythms in cortical areas which also receive information from the skin, joints, and limb muscles. The quantification of respiratory sensation is obtained by psychophysical methods based on different theories linking the stimulus to its perception. Pathological or environmental circumstances act as triggers of the dyspnoea sensation. Ventilatory loading, elicited by dense gas breathing and mostly pathological airway obstruction, leads to an enhanced intrathoracic pressure and respiratory muscle work which in turn activate the vagal and respiratory muscle afferents. Experiments in healthy subjects testify for marked alterations of the tactile sensation and voluntary motor control to limb muscles when the respiratory system is loaded. These viscero-somatic interactions could partly support the well-known phenomenon of altered exercise performances and perception of the body image in patients suffering from chronic respiratory diseases, apart from any disturbances in respiratory gases.