THE ROLE OF THE CAROTID CHEMORECEPTORS IN THE CONTROL OF BREATHING DURING EXERCISE

Our objective was to gain insight into the role of the carotid chemore ceptors (CC) in the exercise hyperpnea. Humans and ponies were studied at rest and during submaximal exercise breathing room air. In healthy humans, alveolar ventilation (V-A) was tightly matched to CO2 product ion (CO2) resulting in PaCO2 deviating during exercise less than 1-2 m m Hg from rest. In contrast, ponies' V-A increased proportionately mor e than VCO2 during exercise resulting in a workload dependent hypocapn ia. Attenuating CC activity through hyperoxia had no effect on exercis e PaCO2 of humans but hyperoxia accentuated the exercise hypocapnia of ponies. Similarly, CC denervation accentuated the exercise hypocapnia of ponies. Healthy humans were also studied while external airway res istance was increased, which, while breathing room air, resulted in a workload dependent hypercapnia, and this hypercapnia was accentuated b y hyperoxia. Finally, a majority of asthmatic humans studied were hype rcapnic during exercise while breathing room air and the hypercapnia w as accentuated by hyperoxia. We conclude that the CC do not provide a primary drive for the exercise hyperpnea but they 'fine tune'' V-A to minimize disruptions of arterial blood gases. In healthy humans, atten uating CC activity has no effect on PaCO2 because the primary V-A driv e is closely matched to VCO2.