48-OR: Changes in Global Cerebral Blood Flow in Response to Hypoglycemia in Type 1 Diabetes Do Not Influence Awareness Status

Abstract

Changes in global cerebral blood flow (gCBF) have been suggested as a mechanism for mitigating the functional impact of hypoglycemia on the brain. The impact of type 1 diabetes (T1D) or hypoglycemia awareness status is not clear. We measured gCBF during progressive lowering of plasma glucose in people with and without T1D, and with retained or impaired awareness of hypoglycemia. Methods: Fifty-one participants (15 with no diabetes (ND), 15 with T1D and normal awareness of hypoglycemia (NAH) and 21 with T1D and impaired awareness of hypoglycemia (IAH)) underwent a two-step hyperinsulinemic hypoglycemic clamp. gCBF was estimated using pseudocontinuous arterial spin labelling magnetic resonance imaging at 6 timepoints: 2 euglycemic, two in the descent phase and two hypoglycemic. gCBF was extracted using a global grey matter mask in SPM12. Statistical analysis and thresholded linear models were performed in R. Results: The mean (+ SD) glucose values at the six timepoints were 95.8 (8.0), 95.5 (9.2), 55.0 (8.3), 50.8 (5.3), 45.7 (4.3) and 45.8 (4.0) mg/dL. Symptom responses to hypoglycemia were absent in IAH. There was a significant increase in CBF in response to hypoglycemia (3-way ANOVA p = 0.04). This was driven by responses in NAH (+7.3%, p < 0.05) and IAH (+10.6% p < 0.01) with no response in ND (+3.5% p = 0.16). The response was not linear, with glucose thresholds of 55.8 mg/dL in NAH and 54.0 mg/dL in IAH (pNAH vs IAH = 0.9) with no threshold in ND. Conclusion: In people with T1D, there is a non-linear relationship between falling glucose and rising gCBF which is not related to awareness status and is not seen in health. The threshold glucose between 54 and 56 mg/dL corresponds closely with level 2 hypoglycemia cut-offs used in current clinical practice. We propose that there is a failure of cerebral vascular autoregulation in response to hypoglycemia in T1D. gCBF responses to hypoglycemia in T1D are independent of symptomatic responses and not responsible for lack of hypoglycemia awareness. Disclosure P. Jacob: None. O. Odaly: None. S. A. Amiel: Advisory Panel; Self; Diabetes UK, Medtronic, Other Relationship; Self; Sanofi, Research Support; Self; Diabetes UK, European Union, JDRF. P. Choudhary: Advisory Panel; Self; Abbott Diabetes, Insulet Corporation, Lilly Diabetes, Medtronic, Sanofi-Aventis, Speaker’s Bureau; Self; Dexcom, Inc., Novo Nordisk. Funding JDRF (3-SRA-2017-484-S-B)