Important role of carotid afferents in control of breathing

The purpose of the present study was todetermine the effect on breathing in the awake state of carotid bodydenervation (CBD) over 1-2 wk after denervation. Studies werecompleted on adult goats repeatedly before and1) for 15 days after bilateral CBD (n = 8),2) for 7 days after unilateral CBD(n = 5), and3) for 15 days after sham CBD(n = 3). Absence of ventilatorystimulation when NaCN was injected directly into a common carotidartery confirmed CBD. There was a significant(P < 0.01) hypoventilation during the breathing of room air after unilateral and bilateral CBD. Themaximum Pa_CO2 increase (8 Torr forunilateral and 11 Torr for bilateral) occurred ~4 days afterCBD. This maximum was transient because by 7 (unilateral)to 15 (bilateral) days after CBD, Pa_CO2 was only 3-4 Torr above control.CO₂ sensitivity was attenuated from control by 60% on day 4 afterbilateral CBD and by 35% on day 4 after unilateral CBD. This attenuation was transient, because CO₂ sensitivity returned tocontrol temporally similar to the return ofPa_CO2 during the breathing of room air.During mild and moderate treadmill exercise 1-8 days afterbilateral CBD, Pa_CO2 was unchanged fromits elevated level at rest, but, 10-15 days after CBD,Pa_CO2 decreased slightly from restduring exercise. These data indicate that1) carotid afferents are animportant determinant of rest and exercise breathing and ventilatoryCO₂ sensitivity, and2) apparent plasticity within theventilatory control system eventually provides compensation for chronicloss of these afferents.