SEVERE HYPOGLYCEMIA UNAWARENESS IS ASSOCIATED WITH AN EARLY DECREASE IN VIGILANCE DURING HYPOGLYCEMIA

To elucidate neurophysiological characteristics in hypoglycaemia unawa reness, we investigated the relationship between electroencephalograph y (EEG) parameters of vigilance and awareness of various symptom categ ories early in response to hypoglycaemia in intensively treated diabet ic patients with different degrees of hypoglycaemia unawareness. Hypog lycaemia (venous plasma glucose below 2.2 mmol/l) was induced with an intravenous insulin bolus in seven patients with insulin-dependent dia betes mellitus (IDDM) with a history of hypoglycaemia unawareness and repeated severe hypoglycaemia, as well as in a group of seven IDDM pat ients with good awareness of hypoglycaemia. Both groups were comparabl e in age, treatment strategy, glycaemic control and level of late comp lications. Basic cognitive performance and other symptom categories we re estimated serially during a period of 2 h following the insulin bol us. A vigilance-controlled EEG was recorded continuously; its automati c analysis included the evaluation of vigilance indices. In the baseli ne prehypoglycaemic state, hypoglycaemia unaware patients showed highe r initial vigilance (p=.05) than the aware group. Unaware patients rep orted fewer neurogenic (p=.002, mainly cholinergic, p=.009) hypoglycae mia symptoms during hypoglycaemia, and developed an impairment in cogn itive performance over time (p=.002). EEG analysis indicated a more ra pid decrease in vigilance after the hypoglycaemic stimulus for unaware patients than for aware patients. The lowering of plasma glucose to 3 .06-3.89 mmol/l already induced a significant increase in delta and th eta, as well as a decrease in alpha relative power only in the unaware group. Differences between groups with regards to the degree of decel eration were most pronounced early, during only slight hypoglycaemia, and topographically spread over central and parietal brain regions. Fu rther lowering of plasma glucose induced an even more pronounced, abru pt increase in slow waves in unaware patients at higher plasma glucose levels than in hypoglycaemia aware subjects (for delta waves at 2.41/-0.16 vs. 1.96+/-0.1 mmol/l, p=.04). This preceded the worsening of c ognitive performance during hypoglycaemia in unaware patients by 19+/- 3 min. Hypoglycaemia unawareness associated with previous unconsciousn ess is associated with-and may be the result of-an early hypoglycaemia -induced reduction in vigilance and an early EEG deceleration, which s eems to be a teleologicallyeffective measure for delaying eventual cer ebral energy failure in hypoglycaemia. Copyright (C) 1996 Elsevier Sci ence Ltd.