Carotid bodies and ventilatory control dynamics in man

The normal role of the carotid bodies in ventilatory dynamics in man has been inferred from studies comparing the responses of a group of control subjects to: a) hypoxic-hyperoxic transitions, b) steady-state hypercapnia, c) constant-load and incremental exercise, and d) breath holding with various inspired O2 levels, with the responses of subjects who had had both carotid bodies surgically resected (CBR). Ventilation, metabolic rate, and alveolar gas tensions were computed breath by breath and blood was sampled from a brachial artery catheter. With eucapnia, hypoxic ventilatory drive is subserved entirely by the carotid bodies, both at rest and during exercise, whereas only approximatly equal to 30% of the hyercapnic response in euoxia is attributable to these structures. CBR resulted in appreciable slowing of the ventilatory dynamics during exercise, causing a transient respiratory acidosis. In the steady state of moderate exercise, ventilation was normal in the CBR group, as other receptors provide the approximately equal to 15% of the drive attributable to the carotid bodies. The respiratory compensation for the acute metabolic acidosis of exercise appears to be exclusively mediated by the carotid bodies. Breath-holding time is significantly prolonged following CBR, especially under hypoxic conditions. The carotid bodies therefore provide important information to respiratory control in man, most notably under hypoxia, metabolic acidosis, and dynamic states of muscular exercise.