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Peripheral chemoreceptors determine the respiratory sensitivity of central chemoreceptors to CO 2 : role of carotid body CO 2
Author(s) -
Smith Curtis. A.,
Blain Grégory M.,
Henderson Kathleen S.,
Dempsey Jerome A.
Publication year - 2015
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jp270114
Subject(s) - hypercapnia , normocapnia , chemoreceptor , hypocapnia , carotid body , central chemoreceptors , anesthesia , tidal volume , hyperpnea , chemistry , ventilation (architecture) , medicine , respiratory system , stimulation , acidosis , mechanical engineering , receptor , engineering
Key Points The influence of specific carotid body (CB) normoxic hypocapnia, hypercapnia and normocapnia on the ventilatory sensitivity of central chemoreceptors to systemic hypercapnia was assessed in seven awake dogs with extracorporeal perfusion of the vascularly isolated CB. Chemosensitivity in this preparation was similar to that in the intact animal. Separation of CB circulation from that of the brain was confirmed. When the isolated CB was hypercapnic vs . hypocapnic and when the isolated CB was normocapnic vs . hypocapnic, the group mean central CO 2 response slopes of minute ventilation ( V ̇ I ) ( P ≤ 0.01) and mean inspiratory flow rate ( V T / T I ) ( P ≤ 0.05) increased significantly. Tidal volume ( V T ), breathing frequency ( f b )and rate of rise of diaphragm EMG were increased in 6 of 7 dogs but did not achieve statistical significance. We propose that hyperaddition is the dominant form of chemoreceptor interaction under conditions of quiet wakefulness in intact animals and over a wide range of CB P C O 2and P O 2 .Abstract We asked if the type of carotid body (CB) chemoreceptor stimulus influenced the ventilatory gain of the central chemoreceptors to CO 2 . The effect of CB normoxic hypocapnia, normocapnia and hypercapnia (carotid body P C O 2 ≈ 22, 41 and 68 mmHg, respectively) on the ventilatory CO 2 sensitivity of central chemoreceptors was studied in seven awake dogs with vascularly‐isolated and extracorporeally‐perfused CBs. Chemosensitivity with one CB was similar to that in intact dogs. In four CB‐denervated dogs, absence of hyper‐/hypoventilatory responses to CB perfusion with P C O 2of 19–75 mmHg confirmed separation of the perfused CB circulation from the brain. The group mean central CO 2 response slopes were increased 303% for minute ventilation ( V ̇ I )( P ≤ 0.01) and 251% for mean inspiratory flow rate ( V T / T I ) ( P ≤ 0.05) when the CB was hypercapnic vs . hypocapnic; central CO 2 response slopes for tidal volume ( V T ), breathing frequency ( f b ) and rate of rise of the diaphragm EMG increased in 6 of 7 animals but the group mean changes did not reach statistical significance. Group mean central CO 2 response slopes were also increased 237% forV ̇ I ( P ≤ 0.01) and 249% for V T / T I ( P ≤ 0.05) when the CB was normocapnic vs . hypocapnic, but no significant differences in any of the central ventilatory response indices were found between CB normocapnia and hypercapnia. These hyperadditive effects of CB hyper‐/hypocapnia agree with previous findings using CB hyper‐/hypoxia.We propose that hyperaddition is the dominant form of chemoreceptor interaction in quiet wakefulness when the chemosensory control system is intact, response gains physiological, and carotid body chemoreceptors are driven by a wide range of O 2 and/or CO 2 .