Respiratory recovery from CO₂ breathing in intact and chemodenervated awake dogs

The transient respiratory recovery from hypercapnia (end tidal = 8% CO₂) in five awake dogs before and after peripheral chemoreceptor denervation was studied. These experiments demonstrate and quantify the contributions of the fast acting peripheral and slower acting central chemoreceptors. Three time constants are identified. Only the first short time constant appears to be associated with the peripheral chemoreceptors. The second and third time constants appear to be centrally mediated. The data indicate that the peripheral contribution to the dynamic response is variable. Based upon means from 31 intact runs and 31 denervated runs it appears that the peripheral chemoreceptors contribute 18% (range of values 8-35%) to the dynamic ventilatory response, have a mean response time constant of 4 sec, and rapidly initiate a decline in ventilation. The peripherally chemodenervated, and hence only centrally mediated, transient ventilatory recovery can be modeled as two time constants of 20 and 118 sec, with contributions of 56% and 44%, respectively, of the total central contribution. This response has a 4 sec greater latency than the intact response.