HYPERK

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This projecte focuses on understanding the physiological effects and fuel needs of the human brain in acute insulin induced hypoglycemia. We have used high field MR perfusion and BOLD imaging in a euglycemic (90-105mg/dl)-hypoglycemic (60mg/dl) clamp in normal human subjeccts to establish the dynamics of cerebral blood flow, oxygen consumption in the resting and task-activated brain. This study has demostrated some very interesting findings under both the euglycemic and hypoglycemic conditions. In particular, in euglycemia we have found that the resting deoxyhemoglobin levels (as evaluated by tissue relaxation measure of R2') is inversely related to the task-activated provoked blood flow. This can be interpreted as: those volunteers who have high efficiency of cerebral oxygen extraction (static deoxyhemoglobin levels are greater if the extraction of oxygen is high) need less of a rise in blood flow to handle the greater demand of oxygen associated with a task This provides a physiological interpretation to the observed variability in R2', flow and potentially BOLD signals (which thus far has been generally assumed to be due to measurement error). This study has also demonstrated that even at a relatively mild hypoglycemic level of 60mg/dl, there is significant rise in cerebral blood flow, from a baseline of 56.8 to 64.5'b18.1ml/100g-min, (p<0.02 paired t-test). While the blood flow increase is seen, there is no effective change in the relaxation rate R2', implying that cerebral metabolism and blood flow remain coupled under these conditions.