Restitution of neurophysiological functions, performance, and subjective symptoms after moderate insulin-induced hypoglycaemia in non-diabetic men

Hypoglycaemia and gastric emptying

Hypoglycaemia is arguably the most important complication of insulin therapy in type 1 and type 2 diabetes. Counter-regulation of hypoglycaemia is dependent on autonomic function and frequent hypoglycaemia may lead to reductions in both autonomic warning signals and the catecholamine response, the so-called "impaired awareness of hypoglycaemia". It is now appreciated that gastric emptying is a major determinant of the glycaemic response to carbohydrate-containing meals in both health and diabetes, that disordered (especially delayed) gastric emptying occurs frequently in diabetes, and that acute hypoglycaemia accelerates gastric emptying substantially. However, the potential relevance of gastric emptying to the predisposition to, and counter-regulation of, hypoglycaemia has received little attention. In insulin-treated patients, the rate of gastric emptying influences the timing of the postprandial insulin requirement, and gastroparesis is likely to predispose to postprandial hypoglycaemia. Conversely, the marked acceleration of gastric emptying induced by hypoglycaemia probably represents an important counter-regulatory response to increase the rate of carbohydrate absorption. This review summarizes the current knowledge of the inter-relationships between hypoglycaemia and gastric emptying, with a focus on clinical implications.

Neurocognitive Function after Cardiac Surgery: From Phenotypes to Mechanisms

For half a century, it has been known that some patients experience neurocognitive dysfunction after cardiac surgery; however, defining its incidence, course, and causes remains challenging and controversial. Various terms have been used to describe neurocognitive dysfunction at different times after cardiac surgery, ranging from "postoperative delirium" to "postoperative cognitive dysfunction or decline." Delirium is a clinical diagnosis included in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5). Postoperative cognitive dysfunction is not included in the DSM-5 and has been heterogeneously defined, though a recent international nomenclature effort has proposed standardized definitions for it. Here, the authors discuss pathophysiologic mechanisms that may underlie these complications, review the literature on methods to prevent them, and discuss novel approaches to understand their etiology that may lead to novel treatment strategies. Future studies should measure both delirium and postoperative cognitive dysfunction to help clarify the relationship between these important postoperative complications.

Hypoglycemia-Induced Changes in the Electroencephalogram: An Overview

Hypoglycemia is defined by an abnormally low blood glucose level. The condition develops when rates of glucose entry into the systematic circulation are reduced relative to the glucose uptake by the tissues. A cardinal manifestation of hypoglycemia arises from inadequate supply of glucose to the brain, where glucose is the primary metabolic fuel. The brain is one of the first organs to be affected by hypoglycemia. Shortage of glucose in the brain, or neuroglycopenia, results in a gradual loss of cognitive functions causing slower reaction time, blurred speech, loss of consciousness, seizures, and ultimately death, as the hypoglycemia progresses. The electrical activity in the brain represents the metabolic state of the brain cells and can be measured by electroencephalography (EEG). An association between hypoglycemia and changes in the EEG has been demonstrated, although blood glucose levels alone do not seem to predict neuroglycopenia. This review provides an overview of the current literature regarding changes in the EEG during episodes of low blood glucose.

Hypoglycemia and safe driving

The lack of awareness of the effects of hypoglycemia on safe driving is a real issue for diabetic patients and a challenge for health care providers. Taking the form of questions and answers, this review addresses the issue of road traffic accidents and drivers with type 1 diabetes mellitus. While there is little evidence showing higher accident rates among diabetic drivers, there is research indicating that hypoglycemia compromises driving performance, resulting in slower response times and reduced cognitive function. Unawareness of an early fall in plasma glucose is another important issue that affects some diabetic drivers. The driver with type 1 diabetes is obliged to check their blood glucose before driving. The physician's duty is to familiarize the patient with the risk of hypoglycemia. If hypoglycemic unawareness is present, the physician should advise the patient to stop driving until the condition is reversed. The doctor should consider informing authorities if he concludes there is a risk and the driver cannot be persuaded to stop driving.

Is hypoglycaemia dangerous?

Tight glycaemic control (TGC) for patients treated in an intensive care unit ICU is associated with an increased risk for hypoglycaemia. Since hypoglycaemia mainly occurs in the sickest patients, no matter whether TGC is applied or not, it might be a marker for severity of illness or a harmful event in itself. Furthermore, it remains a matter of debate whether harmful effects of hypoglycaemia outbalance the clinical benefits of TGC. This review focusses on the clinical manifestations of hypoglycaemia in the critically ill and highlights its potential short- and long-term consequences specifically concerning neurocognitive function.

Delayed recovery of cognitive function following hypoglycemia in adults with type 1 diabetes: effect of impaired awareness of hypoglycemia

OBJECTIVE

Recovery times of cognitive functions were examined after exposure to hypoglycemia in people with diabetes with and without impaired hypoglycemia awareness.

RESEARCH DESIGN AND METHODS

A total of 36 subjects with type 1 diabetes were studied (20 with normal hypoglycemia awareness [NHA] and 16 with impaired hypoglycemia awareness [IHA]). A hyperinsulinemic glucose clamp was used to lower blood glucose to 2.5 mmol/l (45 mg/dl) (hypoglycemia) for 1 h or to maintain blood glucose at 4.5 mmol/l (81 mg/dl) (euglycemia) on separate occasions. Cognitive tests were applied during each experimental condition and were repeated at 10- to 15-min intervals for 90 min after euglycemia had been restored.

RESULTS

In the NHA group, performance was impaired on all cognitive tasks during hypoglycemia and remained impaired for up to 75 min on the choice reaction time (CRT) task (P = 0.03, eta(2) = 0.237). In the IHA group, performance did not deteriorate significantly during hypoglycemia. When all subjects were analyzed within the same general linear model, performance was impaired during hypoglycemia on all tasks. Significant impairment during recovery persisted for up to 40 min on the CRT task (P = 0.04, eta(2) = 0.125) with a significant glycemia-awareness interaction for CRT after one hour of hypoglycemia (P = 0.045, eta(2) = 0.124). Performance on the trail-making B task was impaired for up to 10 min after euglycemia was restored (P = 0.024, eta(2) = 0.158).

CONCLUSIONS

Following hypoglycemia, the recovery time for different cognitive tasks varied considerably. In the IHA group, performance was not significantly impaired during hypoglycemia. The state of awareness of hypoglycemia may influence cognitive function during and after hypoglycemia.

The effects of acute hypoglycaemia on memory acquisition and recall and prospective memory in type 1 diabetes

AIMS/HYPOTHESIS

Global memory performance is impaired during acute hypoglycaemia. This study assessed whether moderate hypoglycaemia disrupts learning and recall in isolation, and utilised a novel test of prospective memory which may better reflect the role of memory in daily life than conventional tests.

SUBJECTS AND METHODS

Thirty-six subjects with type 1 diabetes participated, 20 with normal hypoglycaemia awareness (NHA) and 16 with impaired hypoglycaemia awareness (IHA). Each underwent a hypoglycaemic clamp with target blood glucose 2.5 mmol/l. Prior to hypoglycaemia, subjects attempted to memorise instructions for a prospective memory task, and recall was assessed during hypoglycaemia. Subjects then completed the learning and immediate recall stages of three conventional memory tasks (word recall, story recall, visual recall) during hypoglycaemia. Euglycaemia was restored and delayed memory for the conventional tasks was tested. The same procedures were completed in euglycaemic control studies (blood glucose 4.5 mmol/l).

RESULTS

Hypoglycaemia impaired performance significantly on the prospective memory task (p = 0.004). Hypoglycaemia also significantly impaired both immediate and delayed recall for the word and story recall tasks (p < 0.01 in each case). There was no significant deterioration of performance on the visual memory task. The effect of hypoglycaemia did not differ significantly between subjects with NHA and IHA.

CONCLUSIONS/INTERPRETATION

Impaired performance on the prospective memory task during hypoglycaemia demonstrates that recall is disrupted by hypoglycaemia. Impaired performance on the conventional memory tasks demonstrates that learning is also disrupted by hypoglycaemia. Results of the prospective memory task support the relevance of these findings to the everyday lives of people with diabetes.

Hypoglycaemia and cognitive function

Acute hypoglycaemia impairs cerebral function, and available data indicate that cognitive performance becomes impaired at a blood glucose level of 2.6-3.0 mmol/l in healthy subjects. Methodological problems limit comparisons between studies, but in general complex tasks are more sensitive to hypoglycaemia than simple tasks, and some cognitive abilities are completely abolished. The onset of hypoglycaemic cognitive dysfunction is immediate, but recovery may be considerably delayed. There is persuasive evidence of adaptation to hypoglycaemia, partly due to increased brain glucose uptake capacity, although other mechanisms may exist. Patients who are exposed to chronic or recurrent hypoglycaemia become remarkably tolerant to the state, but this is insufficient to prevent severe hypoglycaemia with neuroglycopenic decompensation, probably because symptomatic and counterregulatory responses adapt even more. During experimental hypoglycaemia, administration of non-glucose cerebral fuels preserves cognitive function. However, little progress has been made as yet towards protecting cognitive function during hypoglycaemia in clinical practice. The chronic effects of recurrent hypoglycaemia remain contentious. There are numerous case reports of hypoglycaemic brain damage and of cognitive deterioration attributed to repeated severe hypoglycaemia. The major prospective studies, including the Diabetes Control and Complications Trial, did not report cognitive declines in intensively treated patients, but had unrepresentative study populations and may have been too short to detect such effects. Structural and functional brain changes are not only associated with recurrent severe hypoglycaemia, but also with hyperglycaemia and early disease onset and may in part be due to hyperglycaemic microvascular disease. Children may be more prone to acute metabolic insults, and there is evidence of developmental disadvantage associated with hypoglycaemic episodes.

Acute hyperglycemia alters mood state and impairs cognitive performance in people with type 2 diabetes

OBJECTIVE

To examine the effects of acute hyperglycemia on cognitive function and mood in people with type 2 diabetes.

RESEARCH DESIGN AND METHODS

Twenty subjects with type 2 diabetes, median age 61.5 years (range 53.1-72.0), known duration of diabetes 5.9 years (range 2.8-11.2), BMI 29.8 kg/m2 (range 22.0-34.6), and HbA1c 7.5% (range 6.7-8.4) were studied. Treatment modalities varied from antidiabetic medications to insulin. A hyperinsulinemic glucose clamp was used to maintain arterialized blood glucose at either 4.5 (euglycemia) or 16.5 mmol/l (hyperglycemia) on two occasions in a randomized and counterbalanced fashion. Tests of information processing, immediate and delayed memory, working memory, and attention were administered, along with a mood questionnaire, during each experimental condition.

RESULTS

Speed of information processing, working memory, and some aspects of attention were impaired during acute hyperglycemia. Subjects were significantly more dysphoric during hyperglycemia, with reduced energetic arousal and increased sadness and anxiety.

CONCLUSIONS

During acute hyperglycemia, cognitive function was impaired and mood state deteriorated in a group of people with type 2 diabetes. These findings are of practical importance because intermittent or chronic hyperglycemia is common in people with type 2 diabetes and may interfere with many daily activities through adverse effects on cognitive function and mood.

Morbidity of hypoglycemia in type 1 diabetes

Hypoglycemia is a common side effect of intensive insulin therapy in patients with type 1 diabetes. Mild hypoglycemia is any episode that can be self-treated, while a severe episode requires external help for recovery. Acute hypoglycemia produces autonomic and neuroglycopenic symptoms, including cognitive impairment and mood changes, while sympathoadrenal stimulation can provoke acute hemodynamic changes with alterations in regional vascular perfusion and a risk of cardiac dysrhythmias. Neurological manifestations include coma, convulsions and focal abnormalities. Long-term morbidities associated with hypoglycemia include impaired awareness of hypoglycemia, counterregulatory hormonal deficiencies, hypoglycemia-associated autonomic failure, and, in rare cases, permanent cognitive impairment. Hypoglycemia affects all aspects of life for the person with type 1 diabetes, including employment, social interactions, driving, sport and leisure activities, and sleep. Appreciation of the potential morbidities of hypoglycemia should encourage physicians to utilize therapeutic regimens that decrease the risk of severe hypoglycemia.

Short-term, delayed, and working memory are impaired during hypoglycemia in individuals with type 1 diabetes

OBJECTIVE

To examine the effects of acute insulin-induced hypoglycemia on short-term, delayed, and working memory in individuals with type 1 diabetes.

RESEARCH DESIGN AND METHODS

A hyperinsulinemic glucose clamp was used to maintain arterialized blood glucose level at either 4.5 mmol/l (euglycemia) or 2.5 mmol/l (hypoglycemia) on two separate occasions in 16 adults with type 1 diabetes. The participants completed tests of immediate and delayed verbal memory, immediate and delayed visual memory, and working memory during each experimental condition. Two other mental tests, the Trail Making B Test and the Digit Symbol Test, were also administered.

RESULTS

Performance in tests of immediate verbal and immediate visual memory was significantly impaired during hypoglycemia. The effect of hypoglycemia on working memory and delayed memory was more profound. Performance in the nonmemory tests, the Trail Making B Test, and the Digit Symbol Test also deteriorated during hypoglycemia.

CONCLUSIONS

All of the memory systems examined in the present study were affected significantly by acute hypoglycemia, particularly working memory and delayed memory. Mild (self-treated) hypoglycemia is common in individuals with insulin-treated diabetes; therefore, these observed effects of hypoglycemia on memory are of potential clinical importance because they could interfere with many everyday activities.

Glucose and glucoregulatory modulation of memory scanning, event-related potentials and EEG in elderly subjects

Endogenous P300b event-related potential (ERP) and behavioral performance measures, extracted during a visual memory scanning task, and spectral indices of resting electroencephalographic (EEG) activity, were assessed in 12 healthy elderly adults before and after double-blind oral administration of a placebo or glucose (50 mg) beverage. Glucoregulation was estimated by deriving a recovery index to categorize subjects as having better (BR) or poorer (PR) blood glucose recovery. Although glucoregulatory status did not impact on EEG or task performance, PR subjects exhibited reduced P300b areas relative to BR subjects prior to beverage administration. Glucose did not alter P300b or memory scanning performance but, regardless of glucoregulatory status, it increased the EEG power in the slow alpha frequency band. The study results suggest that peripheral glucoregulation can influence neuroelectric measures of cognition and that the acute ingestion of glucose can modulate central arousal processes.

Seeing beyond retinopathy in diabetes: electrophysiological and psychophysical abnormalities and alterations in vision

Contrast sensitivity testing, in common with color vision (another test of psychophysical function), demonstrates significant changes in diabetic subjects compared with nondiabetic controls, and there is some evidence for a relationship with grade of retinopathy. Changes in contrast sensitivity have been demonstrated in children and adults with diabetes of short duration, and some evidence exists for a correlation with poor glycemic control, although prospective studies are required to assess this relationship over a longer time period. Although both color vision and contrast sensitivity demonstrate similar patterns, studies that directly compare the two tests suggest that measurement of contrast sensitivity is the more sensitive and specific.

Sustained elevation of cerebral blood flow after hypoglycaemia in normal man

During hypoglycaemia, counter-regulatory hormones are released, cognitive function is impaired and cerebral blood flow is increased. In the immediate period after normalisation of blood glucose only counter-regulatory hormones seem to be normalised. The aim of this study was to follow the changes in cerebral blood flow during a prolonged recovery period following moderate hypoglycaemia in normal man. In 15 healthy men, hypoglycaemia was induced by an intravenous infusion of insulin (2.5 mU/kg per min) to a blood glucose of 2.2 +/- 0.3 mmol/l (mean +/- S.D.) and was kept at this level for 66 +/- 11 min. The cerebral blood flow was measured by a single photon emission computed tomography camera (SPECT) recording the clearance of intravenously administered xenon-133. Measurements were performed before, at the beginning and at the end of the hypoglycaemic period, as well as 23 +/- 5, 51 +/- 7 and 97 +/- 7 min after normalisation of the blood glucose. The basal cerebral blood flow was 50.2 +/- 5.2 ml/100 g per min, increased to 55.6 +/- 4.9 ml/100 g per min (P < 0.001) during hypoglycaemia, and remained at this level at all measurements after normalisation of blood glucose. There was no relation between the rate of fall in blood glucose or level of hypoglycaemia and increment in cerebral blood flow or the actual blood flow during hypoglycaemia. The values of plasma adrenaline, serum ACTH, serum cortisol and symptom scores increased significantly during hypoglycaemia. The adrenaline level was back to the basal level at the first measurement after normalisation of blood glucose, while the ACTH level was normalised at the subsequent measurement and the cortisol level at the last measurement. In conclusion, the results show that despite normalisation of counter-regulatory hormones and hypoglycaemic symptoms, the cerebral blood flow remains elevated for at least 97 +/- 7 min following 66 +/- 11 min of moderate hypoglycaemia, indicating that additional factors which are not coupled to the cerebral metabolism influence this vasculatory response.

Auditory information processing during acute insulin-induced hypoglycaemia in non-diabetic human subjects

Acute insulin-induced hypoglycaemia impairs performance on tests of general mental ability in humans. It is recognized that different brain functions vary in their sensitivity to neuroglycopenia, but little is known about the effects of neuroglycopenia on specific brain processes. The effect of controlled hypoglycaemia on two aspects of auditory information processing (auditory temporal processing and simple auditory processing) was examined in a homogeneous group of 20 healthy non-diabetic human subjects. Auditory temporal processing (temporal order discrimination) and simple auditory processing (pitch discrimination, single-tone duration and single-tone loudness discrimination) tests were part of the Test of Basic Auditory Capabilities (TBAC). Two tests of general cognitive performance (Digit Symbol Substitution and Trail Making B) were included to provide a measure of general brain functioning during hypoglycaemia. Hypoglycaemia lead to a significant deterioration in auditory temporal processing (P < 0.01), and a deterioration in one of three tasks of simple auditory processing (discrimination of single-tone loudness, P < 0.05). Significant disruptions also occurred in both tests of general brain functioning. These results are congruent with other studies in human subjects, showing a disruptive effect of hypoglycaemia on visual information processing when examined under conditions of limited perceptual time, and they provide further evidence of the importance of sensory processing speed in basic perceptual and cognitive functions. The disruptive effect of moderate insulin-induced hypoglycaemia on auditory perception may have implications for insulin-treated diabetic humans exposed to this metabolic stress, because of the importance of hearing in everyday life.

Hypoglycemia as a mitigating factor in vehicular accidents

Cognitive, perceptual, and motor deficits are part of the constellation of symptoms found in various hypoglycemic conditions. Since neurogenic symptoms and altered states of consciousness affect driving skills, hypoglycemia should be considered a mitigating factor in vehicular accidents.