Dynamic changes of CBF, CMRO2, OEF, CMRglc, CBV and ADC during neuronal suppression due to hypothermia

The objective of this study was to test that hypothermia improves the outcome of an acute ischemic stroke. In order to test the hypothesis that hypothermia (32 °C) improves the outcome by effecting the global cerebral reduction of oxygen consumption when the blood flow is already low, we investigated the sequential changes of physiological variables during hypothermia using positron emission tomography (PET) and diffusion-weighted magnetic resonance imaging (DW-MRI) in pigs. The cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) decreased significantly to within 50% of the baseline in 3 and 5 h as functions of time, thereby lowering the viability threshold of the brain tissue. The oxygen extraction fraction (OEF) was significantly elevated to 140% of the baseline in 4 h, indicating a reduction in the driving pressure of oxygen delivery in response to the reduced metabolic need, and then it gradually returned so that it was once again level with the baseline. The cerebral metabolic rate of glucose (CMRglc), the cerebral blood volume (CBV), and apparent diffusion coefficient (ADC) decreased to 75%, 72% and 80% of the baseline after 6 h of hypothermia in response to the lowered metabolism for maintenance of cellular integrity, and the diminution of intracranial pressure. The results of ischemia show that rapid cooling of the brain to 32 °C significantly increases the survival of tissue at risk.