Respiratory sensations during heavy exercise in subjects without respiratory chemosensitivity

Breathlessness arises from increased medullary respiratory center activity projecting to the forebrain (respiratory corollary discharge hypothesis). S ubjects with congenital central hypoventilation syndrome (CCHS) lack the no rmal hyperpnea and breathlessness during hypercapnia. The corollary dischar ge hypothesis predicts that if CCHS subjects have normal hyperpnea during e xercise, they will experience normal breathlessness during exercise. To tes t this, we studied four CCHS subjects and six matched controls during an ex hausting constant-load cycling test requiring substantial anaerobiosis. CCH S subjects rated significantly less breathlessness at the end of the test t han controls, but ventilation (index of respiratory corollary discharge) wa s also somewhat lower in CCHS (not significant). In both groups, breathless ness increased disproportionately more than ventilation towards the end of exercise. These data failed to disprove the corollary discharge hypothesis of breathlessness, but do suggest that the relationship between ventilation and breathlessness is non-linear and/or that projections of chemoreceptor afferents to the forebrain (presumed lacking in CCHS) is one source of brea thlessness in normals. (C) 1998 Elsevier Science B.V. All rights reserved.