IMPORTANT ROLE OF CAROTID AFFERENTS IN CONTROL OF BREATHING

The purpose of the present study was to determine the effect on breath ing in the awake state of carotid body denervation (CBD) over 1-2 wk a fter denervation. Studies were completed on adult goats repeatedly bef ore and 1) for 15 days after bilateral CBD (n = 8), 2) for 7 days afte r unilateral CBD (n = 5), and 3) for 15 days after sham CBD (n = 3). A bsence of ventilatory stimulation when NaCN was injected directly into a common carotid artery confirmed CBD. There was a significant (P < 0 .01) hypoventilation during the breathing of room air after unilateral and bilateral CBD. The maximum Pa-co2 increase (8 Torr for unilateral and 11 Torr for bilateral) occurred similar to 4 days after CBD. This maximum was transient because by 7 (unilateral) to 15 (bilateral) day s after CBD, Pa-co2 was only 3-4 Torr above control. CO2 sensitivity w as attenuated from control by 60% on day 4 after bilateral CBD and by 35% on day 4 after unilateral CBD. This attenuation was transient, bec ause CO2 sensitivity returned to control temporally similar to the ret urn of Pa-co2 during the breathing of room air. During mild and modera te treadmill exercise 1-8 days after bilateral CBD, Pa-co2 was unchang ed from its elevated level at rest, but, 10-15 days after CBD, Pa-co2 decreased slightly from rest during exercise. These data indicate that 1) carotid afferents are an important determinant of rest and exercis e breathing and ventilatory CO2 sensitivity, and 2) apparent plasticit y within the ventilatory control system eventually provides compensati on for chronic loss of these afferents.