title: "Paradoxical" effect of carbon dioxide on common carotid artery blood flow in rabbits during hypothermia and hyperthermia.
abstract: The relative effects of temperature and CO2 on the blood flow in the common carotid artery (CCBF) were investigated in vagotomized, paralyzed rabbits under urethane-chloralose general anaesthesia with artificial ventilation. During hypothermia a 52% fall of CCBF was observed in rabbits ventilated by the classic method. Administration of a hyperkapnic mixture for breathing caused a further 16% CCBF fall, with a simultaneous rise in PaCO2 by 23%. During ventilation with a respirator triggered by phrenic nerve activity hypothermia caused a 30% CCBF fall without changes in PaCO2 value. Administration of the hyperkapnic mixture for breathing caused, in these circumstances, a 9% CCBF fall with a 7% PaCO2 increase. Hyperthermia caused during ventilation by the classic method a 42% rise in CCBF and a 22% PaCO2 rise. The hyperkapnic mixture given for breathing decreased the CCBF by 9% and increased the PaCO2 by 15%. On the other hand, during ventilation with the respirator triggered by phrenic nerve activity no changes were observed in these parameters. This suggests that the thermic stimulus exerts a direct effect on the regulation of the blood flow to the brain, and during hypothermia it prevails over the stimulus produced by CO2.
mesh_terms: D000818:Animals; D002245:Carbon Dioxide / Q000494:pharmacology*; D002339:Carotid Arteries / Q000187:drug effects* / Q000503:physiopathology; D005334:Fever / Q000503:physiopathology*; D007035:Hypothermia / Q000503:physiopathology*; D008297:Male; D011817:Rabbits; D012016:Reference Values; D012039:Regional Blood Flow / Q000187:drug effects; D012121:Respiration, Artificial / Q000379:methods
chemical_list: D002245:Carbon Dioxide