Acute hyperglycemia reduces cerebrovascular reactivity: the role of glycemic variability

Glycemic variability assessed using continuous glucose monitoring in individuals without diabetes and associations with cardiometabolic risk markers: A systematic review and meta-analysis

BACKGROUND & AIMS

Continuous glucose monitoring (CGM) provides data on short-term glycemic variability (GV). GV is associated with adverse outcomes in individuals with diabetes. Whether GV is associated with cardiometabolic risk in individuals without diabetes is unclear. We systematically reviewed the literature to assess whether GV is associated with cardiometabolic risk markers or outcomes in individuals without diabetes.

METHODS

Searches were performed in PubMed/Medline, Embase and Cochrane from inception through April 2022. Two researchers were involved in study selection, data extraction and quality assessment. Studies evaluating GV using CGM for ≥24 h were included. Studies in populations with acute and/or critical illness were excluded. Both narrative synthesis and meta-analyzes were performed, depending on outcome.

RESULTS

Seventy-one studies were included; the majority were cross-sectional. Multiple measures of GV are higher in individuals with compared to without prediabetes and GV appears to be inversely associated with beta cell function. In contrast, GV is not clearly associated with insulin sensitivity, fatty liver disease, adiposity, blood lipids, blood pressure or oxidative stress. However, GV may be positively associated with the degree of atherosclerosis and cardiovascular events in individuals with coronary disease.

CONCLUSION

GV is elevated in prediabetes, potentially related to beta cell dysfunction, but less clearly associated with obesity or traditional risk factors. GV is associated with coronary atherosclerosis development and may predict cardiovascular events and type 2 diabetes. Prospective studies are warranted, investigating the predictive power of GV in relation to incident disease. GV may be an important risk measure also in individuals without diabetes.

An oral glucose tolerance test does not affect cerebral blood flow: role of NOS

Animal data indicate that insulin triggers a robust nitric oxide synthase (NOS)-mediated dilation in cerebral arteries similar to the peripheral tissue vasodilation observed in healthy adults. Insulin's role in regulating cerebral blood flow (CBF) in humans remains unclear but may be important for understanding the links between insulin resistance, diminished CBF, and poor brain health outcomes. We tested the hypothesis that an oral glucose challenge (oral glucose tolerance test, OGTT), which increases systemic insulin and glucose, would acutely increase CBF in healthy adults due to NOS-mediated vasodilation, and that changes in CBF would be greater in anterior regions where NOS expression or activity may be greater. In a randomized, single-blind approach, 18 young healthy adults (24 ± 5 yr) underwent magnetic resonance imaging (MRI) with a placebo before and after an OGTT (75 g glucose), and 11 of these adults also completed an NG-monomethyl-l-arginine (l-NMMA) visit. Four-dimensional (4-D) flow MRI quantified macrovascular CBF and arterial spin labeling (ASL) quantified microvascular perfusion. Subjects completed baseline imaging with a placebo (or l-NMMA), then consumed an OGTT followed by MRI scans and blood sampling every 10-15 min for 90 min. Contrary to our hypothesis, total CBF (P = 0.17) and global perfusion (P > 0.05) did not change at any time point up to 60 min after the OGTT, and no regional changes were detected. l-NMMA did not mediate any effect of OGTT on CBF. These data suggest that insulin-glucose challenge does not acutely alter CBF in healthy adults.

Near-Infrared Spectroscopy: A Free-Living Neuroscience Tool to Better Understand Diabetes and Obesity

The human brain is the least accessible of all organs and attempts to study it in vivo rely predominantly on neuroimaging. Functional near-infrared spectroscopy (fNIRS) allows for the study of cortical neural activity in a non-invasive manner that may resemble free-living conditions. Moreover, compared to other neuroimaging tools, fNIRS is less expensive, it does not require the use of ionizing radiation, and can be applied to all study populations (patients suffering from claustrophobia, or neonates). In this narrative review, we provide an overview of the available research performed using fNIRS in patients with diabetes and obesity. The few studies conducted to date have presented controversial results regarding patients with diabetes, some reporting a greater hemodynamic response and others reporting a reduced hemodynamic response compared to the controls, with an unclear distinction between types 1 and 2. Subjects with obesity or a binge eating disorder have reduced prefrontal activation in response to inhibitory food or non-food stimuli; however, following an intervention, such as cognitive treatment, prefrontal activation is restored. Moreover, we discuss the potential of future applications of fNIRS for a better understanding of cortical neural activity in the context of metabolic disorders.

Glucose variability increases during minimally invasive procedures in very preterm infants

The objective of this study is to assess the effect of neonatal procedures on glucose variability in very preterm infants. Preterm infants (≤ 32 weeks gestation and/or birthweight ≤ 1500 g) were started on continuous glucose monitoring (CGM) on day 2 of birth and monitored for 5 days. Minimally invasive (heel stick, venipunctures) and non-invasive (nappy change, parental presence) procedures were recorded. CGM data were analyzed 30 min before and after each procedure. The primary outcome was the coefficient of glucose variation (CV = SD/mean) before and after the procedure; SD and median glucose were also evaluated. We analyzed 496 procedures in 22 neonates (GA 30.5 weeks [29-31]; birthweight 1300 g [950-1476]). Median glucose did not change before and after each procedure, while CV and SD increased after heel prick (p = 0.017 and 0.030), venipuncture (p = 0.010 and 0.030), and nappy change (p < 0.001 and < 0.001), in the absence of a difference during parental presence.

CONCLUSIONS

Non-invasive and minimally invasive procedures increase glucose variability in the absence of changes of mean glucose.

WHAT IS KNOWN

• Minimally invasive procedures - including nappy change - may increase neonatal stress in preterm infants.

WHAT IS NEW

• Continuous glucose monitoring provides a quantitative measure of neonatal stress during neonatal care procedures demonstrating an increase of glucose variability.

The Rate of Decrease in Brain Perfusion in Progressive Supranuclear Palsy and Corticobasal Syndrome May Be Impacted by Glycemic Variability-A Pilot Study

Progressive supranuclear palsy (PSP) and corticobasal syndrome (CBS) are tauopathic parkinsonian syndromes, presently lacking disease-modifying treatments. Patients affected by these diseases suffer due to multidimensional deteriorations resulting in motor and cognitive impairment. Previously published research has confirmed risk factors that may impact the course of PSP and CBS, among them hypertension and diabetes. Less data is available regarding prediabetes and glycemic variability. In this study, 26 patients with clinical diagnoses of PSP and CBS were examined using glycated hemoglobin and perfusion single-photon emission tomography (SPECT). Patients were divided into two groups-PSP/CBS patients with glycated hemoglobin (HbA1c) below and above 5.7%. The results of the perfusion evaluation were compared with the values from healthy volunteers from the software's database. A decrease in perfusion in certain regions of interest was observed among patients affected by increased glycemic variability. A more pronounced decrement in perfusion was observed only in some regions of interest-the hippocampus, pons, left thalamus, right insula. The results indicated that, among PSP/CBS patients, individuals with more pronounced glycemic variability had more severe hypoperfusion in certain brain regions in comparison with PSP/CBS patients without carbohydrate metabolism disorders. Due to the fact that PSP and CBS are associated with cognitive impairment, an additional decrease in perfusion in the hippocampal area may impact the rate of cognitive deterioration.

Acute glucose fluctuation induces inflammation and neurons apoptosis in hippocampal tissues of diabetic rats

It is well-recognized that glycemic disorders are leading causes of diabetic complications and acute fluctuation of blood glucose and reported more likely being related to oxidative stress, vasculopathy, and other diabetic complications than continuous hyperglycemia in patients with diabetic and animal models. To explore the hypothesis that acute glucose fluctuation (GF) aggravates inflammatory lesions and neuron apoptosis in the hippocampus of diabetic rats. Twenty female GK rats were randomly allocated into a glucose fluctuating group (GK-GF) and a continuous hyperglycemia group (GK-CHG) and 10 age-matched female Wistar rats served as controls. GF was induced in the GK-GF group by injection with glucose and insulin at different periods of time per day for 6 weeks. Body weight was determined weekly. At the end of the study, blood hemoglobin A1c (HbA1c) and serum lipids were measured. Serum and hippocampus interleukin 1β (IL-1β), IL-6, IL-8, and tumor necrosis factor-α (TNF-α) were measured by enzyme-linked immunosorbent assay and real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Hippocampus Bcl-2, Bax, Pten, fas, and myc were quantified by qRT-PCR and Western blot analysis and Mirror Water Maze (MWM) test was performed. We successfully established an animal model with daily GF and a control model with CHG using GK diabetic rats. The GF and CHG rats showed lower weight gain during the 6-week experimental period with no significant difference in the levels of serum lipids such as total triglyceride, total cholesterol, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol compared with the control rats at the end of the study. Meanwhile, the GF and CHG rats showed higher blood HbA1c levels than that of control rats. MWM trainings tests detected that glucose disorders in GF and CHG rats tend to present longer latencies, more cross times and longer path length compared with those of the control rats, indicating impaired the hippocampus-regulated behavioral function such as spatial orientating and memory. Importantly, it was found that GF promoted the expression of TNF-α and IL-1β in the hippocampus of the GF rats while continuous hyperglycemia in CHG rats had little effect on that. Furthermore, both GF and CHG diabetic rats had abnormal expression of apoptosis-associated genes in the hippocampus compared with control Wistar rats and neurons apoptosis in GF rats appears to be more severe than CHG rats. Overall, this study confirmed that GF is a more critical factor that would promote the neuron apoptosis and induce inflammation in the hippocampus than continuous hyperglycemia in diabetic animals, which shed new light on the importance of monitoring and administration of blood glucose in the prevention and therapy for diabetes.

Neonatal Hypoglycemia and Brain Vulnerability

Neonatal hypoglycemia is a common condition. A transient reduction in blood glucose values is part of a transitional metabolic adaptation following birth, which resolves within the first 48 to 72 h of life. In addition, several factors may interfere with glucose homeostasis, especially in case of limited metabolic stores or increased energy expenditure. Although the effect of mild transient asymptomatic hypoglycemia on brain development remains unclear, a correlation between severe and prolonged hypoglycemia and cerebral damage has been proven. A selective vulnerability of some brain regions to hypoglycemia including the second and the third superficial layers of the cerebral cortex, the dentate gyrus, the subiculum, the CA1 regions in the hippocampus, and the caudate-putamen nuclei has been observed. Several mechanisms contribute to neuronal damage during hypoglycemia. Neuronal depolarization induced by hypoglycemia leads to an elevated release of glutamate and aspartate, thus promoting excitotoxicity, and to an increased release of zinc to the extracellular space, causing the extensive activation of poly ADP-ribose polymerase-1 which promotes neuronal death. In this review we discuss the cerebral glucose homeostasis, the mechanisms of brain injury following neonatal hypoglycemia and the possible treatment strategies to reduce its occurrence.

Glycemic Status Assessment by the Latest Glucose Monitoring Technologies

The advanced and performing technologies of glucose monitoring systems provide a large amount of glucose data that needs to be properly read and interpreted by the diabetology team in order to make therapeutic decisions as close as possible to the patient's metabolic needs. For this purpose, new parameters have been developed, to allow a more integrated reading and interpretation of data by clinical professionals. The new challenge for the diabetes community consists of promoting an integrated and homogeneous reading, as well as interpretation of glucose monitoring data also by the patient himself. The purpose of this review is to offer an overview of the glycemic status assessment, opened by the current data management provided by latest glucose monitoring technologies. Furthermore, the applicability and personalization of the different glycemic monitoring devices used in specific insulin-treated diabetes mellitus patient populations will be evaluated.

Compensatory Hippocampal Connectivity in Young Adults With Early-Stage Type 2 Diabetes

CONTEXT

Middle-aged to elderly patients with type 2 diabetes mellitus (T2DM) exhibit reduced functional connectivity and brain atrophy underlying cognitive decrements; however, little is known about brain abnormalities in young patients.

OBJECTIVE

To detect brain anatomical and functional changes in young patients with T2DM during the early disease stage.

DESIGN

Case-control study.

SETTING

Tertiary referral hospital.

PARTICIPANTS

Thirty-five young patients with T2DM (<40 years of age) with no detectable microangiopathy and 32 nondiabetic control subjects.

INTERVENTION

None.

MAIN OUTCOME MEASURES

Subjects underwent neuropsychological assessments and structural and resting-state functional MRI. Both voxel-based morphometry and resting-state functional connectivity analyses were performed.

RESULTS

No significant differences in brain volume were observed between the patients with T2DM and the controls after controlling for age, sex, education, and body mass index. Compared with the controls, the patients showed greater connectivity of the left hippocampus with the left inferior frontal gyrus and the left inferior parietal lobule. Moreover, the enhanced functional connectivity of left hippocampus with the left inferior frontal gyrus significantly correlated with disease severity (urinary albumin-to-creatinine ratio) (r = 0.613, P < 0.001) and executive function (completion time of Stroop Color and Word Test) (r = -0.461, P = 0.005) after false discovery rate correction.

CONCLUSIONS

Our findings suggest an adaptive compensation of brain function to counteract the insidious cognitive decrements during the early stage of T2DM. Additionally, the functional alterations occurring before changes in brain structure and peripheral microangiopathy might serve as early biomarkers related to cognitive decrements.

Continuous Glucose Monitoring Linked to an Artificial Intelligence Risk Index: Early Footprints of Intraventricular Hemorrhage in Preterm Neonates

OBJECTIVE

To develop and validate a new risk score for intraventricular hemorrhage (IVH) in preterm neonates based on continuous glucose monitoring (CGM).

STUDY DESIGN

We retrospectively analyzed CGM traces obtained from 50 very preterm neonates, grouped into two sub-cohorts started on CGM within 12 and 48 h of birth, respectively. A CGM linked to an Artificial Intelligence Risk (CLAIR) index was developed to quantify glucose variability during the first 72 h of life in neonates with and without IVH. Brain-US was performed at least twice a day for the first 5 days of birth. An integrated remote monitoring platform was developed to capture major clinical events in real time and gather data for the risk index. The new score performance was further compared with other measures of glucose variability (coefficient of variation [CV] and standard deviation [SD]) and with a clinical risk index for babies II (CRIB-II) as a predictor of IVH event. The two cohorts were analyzed separately for internal validation of the method.

RESULTS

The primary cohort consisted of 26 neonates (gestational age 30 [28, 31] weeks; BW1275 g[1090, 1750]). Controls (n = 23) exhibited higher CLAIR index than cases (P = 0.004). A cut-off of 0.69 for the new CLAIR index allowed a 100% sensitivity and an 83% specificity for IVH prediction. The CLAIR index was the sole significant predictor for IVH (P = 0.003) when compared with clinical variables, CV, SD, and CRIB-II. In a subgroup analysis in very low-birth-weight infants, the CLAIR index was the sole variable significantly associated with IVH (P = 0.009). Analysis on the secondary cohort (five cases and 16 controls) confirmed a higher CLAIR index in the controls (P = 0.008), in the absence of a difference for CV, SD, and CRIB-II between the two groups.

CONCLUSION

CGM, combined with the AI-algorithm, provides a high-sensitivity index for risk detection of IVH that reflects the glycemic impairment preceding IVH.

Glycemic Variability and Brain Glucose Levels in Type 1 Diabetes

The impact of glycemic variability on brain glucose transport kinetics among individuals with type 1 diabetes mellitus (T1DM) remains unclear. Fourteen individuals with T1DM (age 35 ± 4 years; BMI 26.0 ± 1.4 kg/m²; HbA_1c 7.6 ± 0.3) and nine healthy control participants (age 32 ± 4; BMI 23.1 ± 0.8; HbA_1c 5.0 ± 0.1) wore a continuous glucose monitor (Dexcom) to measure hypoglycemia, hyperglycemia, and glycemic variability for 5 days followed by ¹H MRS scanning in the occipital lobe to measure the change in intracerebral glucose levels during a 2-h glucose clamp (target glucose concentration 220 mg/dL). Hyperglycemic clamps were also performed in a rat model of T1DM to assess regional differences in brain glucose transport and metabolism. Despite a similar change in plasma glucose levels during the hyperglycemic clamp, individuals with T1DM had significantly smaller increments in intracerebral glucose levels (P = 0.0002). Moreover, among individuals with T1DM, the change in brain glucose correlated positively with the lability index (r = 0.67, P = 0.006). Consistent with findings in humans, streptozotocin-treated rats had lower brain glucose levels in the cortex, hippocampus, and striatum compared with control rats. These findings that glycemic variability is associated with brain glucose levels highlight the need for future studies to investigate the impact of glycemic variability on brain glucose kinetics.

Effect of the GSTM1 gene deletion on glycemic variability, sympatho-vagal balance and arterial stiffness in patients with metabolic syndrome, but without diabetes

AIMS

An increased rate of cerebrovascular complications in patients with metabolic syndrome (MetS) has been reported. Previous studies demonstrated an association between glycemic variability (GV) and cerebrovascular reactivity (CRV) in MetS, thus suggesting a putative role of GV on cerebrovascular events. Although the pathophysiological mechanism linking GV to damage is still to be elucidated, evidence suggests oxidative stress plays a crucial role. Since functional variants in glutathione S-transferases (GST) genes modulate the cellular detoxification processes, the aim of this study was to elucidate the involvement of GSTs in MetS and investigating the correlation with GV, arterial stiffness, and sympatho-vagal (SV) balance.

METHODS

A hundred metabolic syndrome patients without diabetes underwent GST gene polymorphism analysis and a sub-sample 36 patients were randomly selected to investigate the correlation between GST gene polymorphisms and GV, and sympatho-vagal (SV) balance and arterial stiffness.

RESULTS

GSTM1 showed a significant association with several GV, arterial stiffness, and SV balance indexes. In particular, the GSTM1 deletion positively correlates with lower values of these indexes when compared to the presence of the gene.

CONCLUSIONS

Therefore, we suggested a global influence of GSTM1 deletion on the GV, arterial stiffness, and SV balance pathways in MetS patients, probably also interacting with AMP-activated protein kinase (AMPK) regulation. Our novel findings indicate GSTM1 could be a risk locus in MetS development and shed light novel scenarios on the role of glucose fluctuations in neurological impairments.

Insulin resistance among obese middle-aged is associated with decreased cerebrovascular reactivity

OBJECTIVE

To evaluate differences in cerebrovascular reactivity (CVR) to mild hypercapnia in obese/overweight individuals with and without insulin resistance (IR) compared to comparable lean controls.

METHODS

A total of 60 cognitively normal participants (20 lean controls and 24 obese/overweight individuals with and 16 without IR) were evaluated using a high spatial resolution arterial spin labeling MRI technique at rest and during mild hypercapnia. We analyzed group differences in CVR in cerebral cortex and ascertained the relationships between CVR, IR, and body mass index (BMI).

RESULTS

Obese/overweight participants with and without IR had significantly lower CVR to hypercapnia than lean controls after controlling for age, sex, and the presence of hypertension (F_2,53 = 5.578, p = 0.006 [Formula: see text] = 0.174). In the obese/overweight participants with IR, there was a significant correlation between higher CVR and a measure of insulin sensitivity, even after accounting for BMI (r_p = 0.575, p = 0.004). In contrast, there was no relationship between CVR and BMI when controlling for IR. No such relationships existed for the other 2 groups.

CONCLUSIONS

IR is associated with impaired CVR; the relationship appears to be driven by the degree of IR and not by obesity. These rarely reported results suggest that early forms of cerebrovascular dysfunction exist among obese middle-aged individuals with significant IR but without type 2 diabetes mellitus. These functional vascular abnormalities may help explain the associations among IR, diabetes, and dementia, and suggest that interventions aiming to improve IR or CVR may help prevent cognitive decline later in life.

Retinal neurodegeneration in patients with type 1 diabetes mellitus: the role of glycemic variability

AIMS

Recent studies have identified neuroretinal abnormalities in persons affected by diabetes mellitus, before the onset of microvascular alterations. However, the role of glycemic variability (GV) on early retinal neurodegeneration is still not clarified.

METHODS

To explore the relationship between glycemic control and neuroretinal characteristics, 37 persons with Type 1 diabetes mellitus (Type 1 DM) divided into two groups with no signs (noRD) and with mild non-proliferative diabetic retinopathy (NPDR) compared to 13 healthy control participants (C) were recruited. All persons underwent an optical coherence tomography with automatic segmentation of all neuroretinal layers. Measurements of mean of nasal (N)/temporal (T)/superior (S)/inferior (I) macular quadrants for individual layer were also calculated. Metabolic control was evaluated by glycated hemoglobin (HbA1c), and indexes of GV were calculated from continuous glucose monitoring.

RESULTS

The difference among the three groups in terms of RNFL thickness was significantly dependent on quadrant (F(6;132) = 2.315; p = 0.037). This interaction was due to a specific difference in RNFL-N thickness, where both Type 1 DM groups showed a similar reduction versus C (-3.9 for noDR and -4.9 for NPDR), without any relevant difference between them (-1.0). Inner nuclear layer (INL) was increased in all quadrants in the two Type 1 DM groups compared to C (mean difference = 7.73; 95% CI: 0.32-15.14, p = 0.043; mean difference = 7.74; 95% CI: 0.33-15.15, p = 0.043, respectively). A negative correlation between RNFL-N and low blood glucose index (r = -0.382, p = 0.034) and positive correlation between INL and continuous overall net glycemic action -1, -2, -4 h (r = 0.40, p = 0.025; r = 0.39, p = 0.031; r = 0.41, p = 0.021, respectively) were observed in Type 1 DM patients. The triglycerides were positively and significantly correlated to INL (r = 0.48, p = 0.011), in Type 1 DM subjects. GV and triglycerides resulted both independent predictors of increased INL thickness. No correlation was found with HbA1c.

CONCLUSIONS

Early structural damage of neuroretina in persons with Type 1 DM patients is related to glucose fluctuations. GV should be addressed, even in the presence of a good metabolic control.

The impact of basal insulin analogues on glucose variability in patients with type 2 diabetes undergoing renal replacement therapy for end-stage renal disease

PURPOSE

We aimed to analyze the impact of basal insulin analogues on glucose variability (GV) in patients with type 2 diabetes (DM) undergoing renal replacement therapy.

METHODS

Fourteen subjects on insulin therapy for at least 6 months (detemir, n = 7 vs. glargine, n = 7) were sequentially enrolled in this prospective study. Continuous glucose monitoring system (CGMS Gold, Dex Com 7+) was applied for 5 days, over 3 consecutive sessions of hemodialysis (HD). Various glycemic profiles (coefficient of variation-CV of mean glucose) were compared between the day on (HD-on) and the day off (HD-off) dialysis. The CV of at least 3 values of HbA1c (HPLC) since replacement therapy has been applied to assay the long-term GV. Endogenous insulin and insulin resistance (HOMA using fasting glucose and C-peptide levels), fasting lipid profile, quantitative C-reactive protein (CRP) and ferritin (values adjusted for Hb) were measured in serum at inclusion.

RESULTS

The overnight HD-off and HD-on short-term (CV CGMS) GV, overall long-term (CV of HbA1c) GV, CRP and ferritin were reduced in subjects treated with detemir (paired t test, p = 0.0001, 0.0011, 0.036, <0.001, and <0.001 between groups). All participants were insulin-resistant (HOMA-IR > 3).

CONCLUSIONS

Insulin-resistant patients with type 2 diabetes undergoing hemodialysis for end-stage renal disease on insulin detemir exhibit lower glycemic variability and pro-inflammatory profile than with insulin glargine.

Regional cerebral hemodynamic response to incremental exercise is blunted in poorly controlled patients with uncomplicated type 1 diabetes

OBJECTIVE

Cerebral vasoreactivity to pharmacologically induced hypercapnia is impaired in poorly controlled patients with type 1 diabetes but otherwise free from microangiopathy. However, whether this response is also compromised during exercise, a daily-life physiological condition challenging regional cerebral hemodynamics, is unknown. We aimed to investigate prefrontal cortex hemodynamics during incremental maximal exercise in patients with uncomplicated type 1 diabetes, taking into account long-term glycemic control as well as exercise- and diabetes-influenced vasoactive stimuli.

RESEARCH DESIGN AND METHODS

Two groups of patients (type 1 diabetes with adequate glycemic control [T1D-A], n = 8, HbA1c 6.8 ± 0.7% [51 ± 7.7 mmol/mol]; type 1 diabetes with inadequate glycemic control [T1D-I], n = 10, HbA1c 9.0 ± 0.7% [75 ± 7.7 mmol/mol]) were compared with 18 healthy control subjects (CON-A and CON-I) matched for physical activity and body composition. Throughout exercise, near-infrared spectroscopy allowed investigation of changes in oxyhemoglobin (O2Hb), deoxyhemoglobin (HHb), and total hemoglobin (THb) in the prefrontal cortex. Venous and arterialized capillary blood was sampled during exercise to assess for factors that may alter prefrontal cortex hemodynamics and oxygenation.

RESULTS

No differences were observed between T1D-A and CON-A, but VO2max was impaired (P < 0.05) and cerebral blood volume (THb) increase blunted (P < 0.05) in T1D-I compared with CON-I. Nonetheless, O2Hb appeared unaltered in T1D-I probably partly due to blunting of simultaneous neuronal oxygen extraction (i.e., a lower HHb increase; P < 0.05). There were no intergroup differences in arterial oxygen content, Paco2, pH, [K(+)], and free insulin levels.

CONCLUSIONS

Maximal exercise highlights subtle disorders of both hemodynamics and neuronal oxygenation in the prefrontal cortex of poorly controlled patients with type 1 diabetes. These findings may warn clinicians of brain endothelial dysfunction occurring even before overt microangiopathy during exercise.