Coupling of cerebral blood flow and oxygen metabolism in infant pigs during selective brain hypothermia

Studies documenting the cerebral hemodynamic consequences of selective brai n hypothermia (SBH) have yielded conflicting data. Therefore, the authors h ave studied the effect of SBH on the relation of cerebral blood flow (CBF) and CMRO2 in the forebrain of pigs. Selective brain hypothermia was induced in seven juvenile pigs by bicarotid perfusion of the head with extracorpor ally cooled blood. Cooling and stepwise rewarming of the brain to a T-brain of 38 degrees C, 25 degrees C, 30 degrees C, and 38 degrees C at normother mic T-trunk (38 degrees C) decreased CBF from 71 +/- 12 mL 100 g(-1) min(-1 ) at normothermia to 26 +/- 3 mL 100 g(-1) min(-1) and 40 +/- 12 mL 100 g(- 1) min(-1) at a T-brain of 25 degrees C and 30 degrees C, respectively. The decrease of CMRO2 during cooling of the brain to a T-brain of 25 degrees C resulted in a mean Q(10) of 2.8. The ratio between CBF and CMRO2 was incre ased at a T-brain of 25 degrees C indicating a change in coupling of flow a nd metabolism. Despite this change, regional perfusion remained coupled to regional temperatures during deep cerebral hypothermia. The data demonstrat e that SBH decreases CBF and oxygen metabolism to a degree comparable with the cerebrovascular and metabolic effects of systemic hypothermia. The auth ors conclude that, irrespective of a change in coupling of blood flow and m etabolism during deep cerebral hypothermia, cerebral metabolism is a main d eterminant of CBF during SBH.