Role of cerebral fluids in control of respiration as studied in unanesthetized goats

Abstract

Respiratory responses to inhaled CO 2 were measured in unanesthetized goats during repeated perfusions of the ventriculocisternal system through chronically implanted cannulas. [HCO 3 – ] and pH were measured in carotid loop blood and cisternal outflow. Average steady-state alveolar ventilation increased fourfold when cerebrospinal fluid (CSF)-[HCO 3 – ] was reduced from 30 to 15 mm/liter at constant, normal CO 2 pressure or threefold when CSF pH changed from 7.32 to 7.21 at constant, normal CSF-[HCO 3 – ]. Sensitivity was two- to sevenfold greater than reported for anesthetized animals. At constant CSF pH the ventilatory response to inhaled CO 2 was 60% of the isobicarbonate response. Pco 2 in cisternal outflow was shown to approximate that in cerebral tissue. HCO 3 – flux was measured as a function of CSF-[HCO 3 – ] and concentration profiles between CSF and capillary blood were considered. Alveolar ventilation is a single linear function of [H + ] in tissue fluid located two-thirds to three-fourths of the distance along the functional concentration gradient of HCO 3 – between CSF and blood at all values of Pco 2 and CSF-[HCO 3 – ] which we investigated.