Exercise-related Hypoglycemia Research Articles

Hemostatic Effects of Exercise-Related Hypoglycemia in Male Persons With Type 1 Diabetes.

People with type 1 diabetes (T1D) are at increased risk of thrombosis, however, the underlying mechanisms remain unclear. Hypoglycemia induced at rest can induce coagulation activation, but little is known about the hemostatic effects of exercise-related hypoglycemia in people with T1D. We compared hemostatic profiles of individuals with T1D with healthy controls and explored hemostatic effects of hypoglycemia, induced with or without exercise, in participants with T1D. Thrombelastography (TEG) was used for a baseline hemostatic comparison between fifteen men with T1D and matched healthy controls. In addition, the participants with T1D underwent two euglycemic-hypoglycemic clamp days in a randomized, crossover fashion. Hypoglycemia was induced with the participants at rest (Hypo-rest) or during exercise (Hypo-exercise). TEG provides data on the rate of coagulation activation (R-time), the rate of clot formation (K-time, α-Angle), the maximum clot amplitude (MA), the functional fibrinogen contribution to the clot strength (MA-FF) and the fibrinolysis (LY-30). The T1D group exhibited shorter R-time and K-time and a greater α-Angle compared to the controls. During the clamp experiments, Hypo-exercise induced an increased clot strength (MA) with a mean difference from baseline of 2.77 mm [95% confidence interval 2.04; 3.51] accompanied with a decreased fibrinolysis (LY-30) of -0.45 percentage points [-0.60; -0.29]. Hypo-rest resulted in increased functional fibrinogen (MA-FF) of 0.74 mm [0.13; 1.36] along with an increased fibrinolysis (LY-30) of 0.54 percentage points [0.11; 0.98]. Individuals with T1D exhibit a hypercoagulable hemostatic profile compared to healthy controls and exercise-related hypoglycemia may increase the susceptibility to thrombosis via both procoagulant and antifibrinolytic effects.

Accuracy of continuous glucose monitoring during exercise-related hypoglycemia in individuals with type 1 diabetes.

Hypoglycemia is common in individuals with type 1 diabetes, especially during exercise. We investigated the accuracy of two different continuous glucose monitoring systems during exercise-related hypoglycemia in an experimental setting. Fifteen individuals with type 1 diabetes participated in two separate euglycemic-hypoglycemic clamp days (Clamp-exercise and Clamp-rest) including five phases: 1) baseline euglycemia, 2) plasma glucose (PG) decline ± exercise, 3) 15-minute hypoglycemia ± exercise, 4) 45-minute hypoglycemia, and 5) recovery euglycemia. Interstitial PG levels were measured every five minutes, using Dexcom G6 (DG6) and FreeStyle Libre 1 (FSL1). Yellow Springs Instruments 2900 was used as PG reference method, enabling mean absolute relative difference (MARD) assessment for each phase and Clarke error grid analysis for each day. Exercise had a negative effect on FSL1 accuracy in phase 2 and 3 compared to rest (ΔMARD = +5.3 percentage points [(95% CI): 1.6, 9.1] and +13.5 percentage points [6.4, 20.5], respectively). In contrast, exercise had a positive effect on DG6 accuracy during phase 2 and 4 compared to rest (ΔMARD = -6.2 percentage points [-11.2, -1.2] and -8.4 percentage points [-12.4, -4.3], respectively). Clarke error grid analysis showed a decrease in clinically acceptable treatment decisions during Clamp-exercise for FSL1 while a contrary increase was observed for DG6. Physical exercise had clinically relevant impact on the accuracy of the investigated continuous glucose monitoring systems and their ability to accurately detect hypoglycemia.

Severe Hypoglycemia and the Use of Glucagon Rescue Agents: An Observational Survey in Adults With Type 1 Diabetes.

Severe hypoglycemia (SH) is the most frequent and potentially serious complication affecting individuals with type 1 diabetes and can have major clinical and psychosocial consequences. Glucagon is the only approved treatment for SH that can be administered by non-health care professionals (HCPs); however, reports on the experiences and emotions of people with type 1 diabetes associated with SH and glucagon rescue use are limited. This survey study demonstrated that an increasing number of individuals with type 1 diabetes have current and filled prescriptions for glucagon and have been educated about glucagon rescue use by an HCP. Despite this positive trend, challenges with SH remain, including a high level of health care resource utilization, considerable out-of-pocket expenses for glucagon kits, a high prevalence of hypoglycemia unawareness, and a negative emotional impact on individuals with diabetes. Nocturnal and exercise-related hypoglycemia were concerns for most survey participants.

377-P: Exercise-Related Hypoglycemia Induces Hypercoagulable Changes in Patients with Type 1 Diabetes

Diabetes is a hypercoagulable state predisposing to cardiovascular disease. Physical exercise can improve cardiovascular health but may also cause hypoglycemia in insulin-treated patients. We compared hemostatic profiles of patients with type 1 diabetes (T1D) with healthy controls and delineated hemostatic changes of hypoglycemia, induced with or without exercise, in patients with T1D. Thromboelastography (TEG®6s) was used to compare hemostatic profiles of patients with T1D (N=15, (mean±SD) age 29.4±8.1 years, HbA1c 6.8±0.5%, diabetes duration 13.1±6.2 years, BMI 23.7±2.0 kg/m2) with individually matched healthy controls (N=15) . In addition, the patients with T1D underwent (randomized, crossover design) two separate hyperinsulinemic euglycemic-hypoglycemic clamp days. During decline in plasma glucose and the initial 15 min of hypoglycemia, the subjects were either resting or performing moderate-intensity exercise. TEG was performed at baseline euglycemia and after 15 min and 60 min of hypoglycemia. Compared with healthy controls, patients with T1D were more hypercoagulable with shorter R-time (P<0.001) and K-time (P=0.019) and an increased Angle-value (P=0.009) . Clot maximum amplitude (MA) , functional fibrinogen (MA-FF) , and fibrinolysis (LY-30) were similar in the two groups. In patients with T1D, exercise-related hypoglycemia induced hypercoagulable changes with decreased K-time (P=0.005) , increased Angle-value (P=0.049) , and increased MA (P<0.001) after 15 min of hypoglycemia. These changes were not compensated by an increased fibrinolysis. In contrast, hypoglycemia induced at rest resulted in decreased K-time (P=0.03) and increased MA-FF (P=0.02) only after 60 min, along with increased LY-30 (P=0.02) . In conclusion, patients with T1D have a more hypercoagulable profile than healthy controls, and exercise-related hypoglycemia induces coagulation without a compensatory fibrinolytic activity, which may increase susceptibility for thrombosis. Disclosure P.G.Hagelqvist: None. A.Andersen: n/a. K.Maytham: None. S.Engberg: Employee; Novo Nordisk A/S. U.Pedersen-bjergaard: Advisory Panel; Novo Nordisk A/S, Sanofi. P.I.Johansson: None. F.K.Knop: Advisory Panel; Boehringer Ingelheim International GmbH, Eli Lilly and Company, Merck Sharp & Dohme Corp., Novo Nordisk, Sanofi, ShouTi, Zucara Therapeutics, Consultant; AstraZeneca, Eli Lilly and Company, Novo Nordisk, Pharmacosmos A/S, Sanofi, ShouTi, Zealand Pharma A/S, Zucara Therapeutics, Research Support; AstraZeneca, Novo Nordisk, Sanofi, Zealand Pharma A/S, Speaker's Bureau; AstraZeneca, Bayer AG, Boehringer Ingelheim International GmbH, Eli Lilly and Company, Novo Nordisk, Sanofi, Stock/Shareholder; Antag Therapeutics. T.Vilsbøll: Consultant; AstraZeneca, Bristol-Myers Squibb Company, Eli Lilly and Company, Gilead Sciences, Inc., GlaxoSmithKline plc., Merck Sharp & Dohme Corp., Mundipharma, Novo Nordisk, Sun Pharmaceutical Industries Ltd. Funding Independent research fund Denmark (1030-00256B) Grosserer L.F. Foghts Fund (21.761)

694-P: Assessing Social Support in Diabetes Camp

Social and family support in diabetes predicts self-efficacy, adherence, and positive health outcomes. Peer and family support are explicit strengths of youth possessing resilience to flourish despite challenges of diabetes. Interest in strength-based assessment and interventions in pediatric diabetes practices is increasing in recognition that youth spend significant time away from home and management responsibilities shift away from parents. Nearly 150 diabetes camps reach 25,000 children annually. Camps demonstrate improved self-efficacy and self-confidence. We examined whether youth attending a sports-based day camp exhibit resilience factors that can impact diabetes-related distress levels related to participating in exercise. With parent consent, 44 youth (8-17 year) completed the Diabetes Strengths and Resilience Measure (DSTAR) the first day of camp. Factors related to diabetes confidence and management skewed high with scores of often or almost always for most of the 12- item survey. Mean parental help/support with diabetes was high at 3.6 (of 4) as 90% of youth identified they often/almost always get parental help. Friend support was the lowest scoring factor with mean of 2.6 for youth telling friends about diabetes. Often or almost always was chosen by 50% of youth, 32% sometimes, and 18% never. Counting on friends if I need help scored lowest (mean 2.1) as 35% chose never/rarely, 21% sometime, and 44% often/almost always. Parent surveys indicated 100% of children are physically active 1 hour/day nearly every day (70% 5-7 days/week, 30% 2-4 days/week). Hypoglycemia frequency was 5.5/month (44% >9). In conclusion, youth with type 1 diabetes who are physically active and at risk for frequent hypoglycemia do not share their diabetes needs with friends and rarely feel they can count on friends to help them (such as recognizing/treating exercise related hypoglycemia). Camps are non-clinical venues to assess social support and intervene with non-traditional age-appropriate education. Disclosure C.A. Beebe: Consultant; Self; Xeris Pharmaceuticals, Inc. M.T. Joyce: None. T. Alesia: None.

The Role of Physical Exercise in Obesity and Diabetes.

The prevalence of obesity is increasing world-wide. Obesity is associated with a plethora of metabolic and clinical constraints, which result in a higher risk for the development of cardiovascular complications and metabolic disease, particularly insulin resistance and type 2 diabetes. Obesity is an acknowledged determinant of glycemic control in patients with type 1 diabetes and accounts for the majority of premature death due to cardiovascular events. Physical exercise is generally recommended in patients with diabetes in order to prevent the development of or reduce existing obesity, as adopted by every international treatment guideline so far. Regular physical exercise has a beneficial impact on body composition, cardiovascular integrity, insulin sensitivity and quality of life. However, only a minority of patients participates in regular physical exercise, due to individual or disease-related barriers. In type 2 diabetes, there is robust evidence for beneficial effects of physical exercise on glycemic control, cardiovascular health and the development of diabetes-related long-term complications. In type 1 diabetes and patients treated with insulin, a higher risk for exercise-related hypoglycemia has to be considered, which requires certain prerequisites and adequate adaptions of insulin dosing. Current treatment guidelines do only incompletely address the development of exercise-related hypoglycemia. However, every patient with diabetes should participate in regular physical exercise in order to support and enable sufficient treatment and optimal glycemic control.

Predicting Exercise-Related Changes in Glucose in People with Type 1 Diabetes Using Linear Models and Incorporating Knowledge of Prior Exercise

Exercise-related hypoglycemia in T1D is frequent and can be life-threatening. The ability to predict glucose changes at the start of exercise could significantly improve exercise outcomes for people with T1D. We developed multivariate adaptive regression splines (MARS) to predict changes to blood glucose dynamics and to assess whether including past glucose changes during exercise improves prediction accuracy. Data was collected from 20 adults during a 4-arm, 4-day, outpatient artificial pancreas (AP) study (14 F, weight: 76.3 ±14.6 kg, age: 35.2 ± 4.6 years, height: 172.0 ± 10.6 cm). Days 1 and 4 of the study consisted of identical controlled meals and aerobic exercise events at an academic medical center. Insulin delivery data, heart rate, continuous glucose measurement (CGM) data, and carbohydrate intake were recorded. Subjects exercised at 60% of their maximal VO2 for 45 minutes. Using the 160 aerobic exercise sessions, 2 linear predictive models were developed to estimate glucose drop during exercise: (1) a model excluding past exercise history (naïve), and (2) a model including past exercise (historical). A greedy approach was used to eliminate non-predictive features and build sparse models consisting of CGM at the start of exercise, the rate of change of CGM within 5 minutes of exercise, the metabolic expenditure 5 minutes into exercise, and participant height. Leave-one-out cross validation was done to fit the model and estimate root-mean squared error (RMSE). R2 was calculated between empirical and predicted glucose drops. The naïve model was able to predict glucose drop to within 18.7 mg/dL. Including historical exercise data improved accuracy and increased R2 only nominally (naïve R2=0.78, RMSE=18.7, historical R2= 0.81, RMSE=17.54). Results demonstrate prediction accuracy of linear models in estimating exercise-related glucose changes with moderate improvement by including prior exercise data. Disclosure N.S. Tyler: None. R. Reddy: None. J. El Youssef: None. J.R. Castle: Consultant; Self; Zealand Pharma A/S. Advisory Panel; Self; Novo Nordisk Inc. P.G. Jacobs: Stock/Shareholder; Self; Pacific Diabetes Technologies.

Randomized Outpatient Trial of Single- and Dual-Hormone Closed-Loop Systems That Adapt to Exercise Using Wearable Sensors.

OBJECTIVEAutomated insulin delivery is the new standard for type 1 diabetes, but exercise-related hypoglycemia remains a challenge. Our aim was to determine whether a dual-hormone closed-loop system using wearable sensors to detect exercise and adjust dosing to reduce exercise-related hypoglycemia would outperform other forms of closed-loop and open-loop therapy.RESEARCH DESIGN AND METHODSParticipants underwent four arms in randomized order: dual-hormone, single-hormone, predictive low glucose suspend, and continuation of current care over 4 outpatient days. Each arm included three moderate-intensity aerobic exercise sessions. The two primary outcomes were percentage of time in hypoglycemia (<70 mg/dL) and in a target range (70–180 mg/dL) assessed across the entire study and from the start of the in-clinic exercise until the next meal.RESULTSThe analysis included 20 adults with type 1 diabetes who completed all arms. The mean time (SD) in hypoglycemia was the lowest with dual-hormone during the exercise period: 3.4% (4.5) vs. 8.3% (12.6) single-hormone (P = 0.009) vs. 7.6% (8.0) predictive low glucose suspend (P < 0.001) vs. 4.3% (6.8) current care where pre-exercise insulin adjustments were allowed (P = 0.49). Time in hypoglycemia was also the lowest with dual-hormone during the entire 4-day study: 1.3% (1.0) vs. 2.8% (1.7) single-hormone (P < 0.001) vs. 2.0% (1.5) predictive low glucose suspend (P = 0.04) vs. 3.1% (3.2) current care (P = 0.007). Time in range during the entire study was the highest with single-hormone: 74.3% (8.0) vs. 72.0% (10.8) dual-hormone (P = 0.44).CONCLUSIONSThe addition of glucagon delivery to a closed-loop system with automated exercise detection reduces hypoglycemia in physically active adults with type 1 diabetes.

The Role of Physical Exercise in Obesity and Diabetes

The prevalence of obesity is increasing world-wide. Obesity is associated with a plethora of metabolic and clinical constraints, which result in a higher risk for the development of cardiovascular complications and metabolic disease, particularly insulin resistance and type 2 diabetes. Obesity is an acknowledged determinant of glycemic control in patients with type 1 diabetes and accounts for the majority of premature death due to cardiovascular events. Physical exercise is generally recommended in patients with diabetes in order to prevent the development of or reduce existing obesity, as adopted by every international treatment guideline so far. Regular physical exercise has a beneficial impact on body composition, cardiovascular integrity, insulin sensitivity and quality of life. However, only a minority of patients participates in regular physical exercise, due to individual or ­disease-related barriers. In type 2 diabetes, there is robust evidence for beneficial effects of physical exercise on glycemic control, cardiovascular health and the development of diabetes-related long-term complications. In type 1 diabetes and patients treated with insulin, a higher risk for exercise-­related hypoglycemia has to be considered, which requires certain prerequisites and adequate adaptions of insulin ­dosing. Current treatment guidelines do only incompletely address the development of exercise-related hypoglycemia. However, every patient with diabetes should participate in regular physical exercise in order to support and enable ­sufficient treatment and optimal glycemic control.

Strategies used by Patients with Type 1 Diabetes to Avoid Hypoglycemia in a 24×1-Hour Marathon: Comparison with the Amounts of Carbohydrates Estimated by a Customizable Algorithm.

The preferred countermeasure to avoid exercise-related hypoglycemia was investigated in a group of patients with type 1 diabetes participating in a stressful event, a 24×1-hour relay marathon. The carbohydrates actually consumed were compared to those estimated for each patient by applying a customizable algorithm, Exercise Carbohydrates Requirement Estimating Software (ECRES), based on patient's usual therapy and diet and on the exercise characteristics. Glycemia was tested at the start, middle and end of the races. Usual therapies and diets and the adopted countermeasures were recorded in detail. We studied 19 patients who walked/ran 10.4±2.8 km with a heart rate of 167±11 beats per minute. Of the 19 patients, 7 patients reduced the administered insulin (premeal bolus or basal infusion rate). Glycemia fell by the end of the races (p=0.006; median -1.8 mmol⋅L-1; interquartile range -0.4 mmol⋅L-1 to -5.3 mmol⋅L-1), despite 9 patients being hyperglycemic at the start. Of the patients, 14 concluded the race with glycemia on target, and 4 patients were hyperglycemic. Amounts of carbohydrates actually consumed (median 30 g; interquartile range 0 g to 71 g) were not significantly different from those estimated by ECRES (median 38 g; interquartile range 24 g to 68 g), the 2 quantities being significantly related (R=0.64; p=0.003). ECRES estimated lower carbohydrate levels (-13 g) than the amounts actually consumed by the 4 patients who concluded their exercises with hyperglycemia. Patients preferred to consume extra carbohydrates to avoid the possible exercise-induced hypoglycemia. ECRES would provide satisfactory estimates of the carbohydrate requirements, even for a stressful condition, and almost equal to the quantities consumed following medical advice.

The Impact of Accelerometer and Heart Rate Data on Hypoglycemia Mitigation in Type 1 Diabetes.

Aerobic exercise can lower blood glucose levels and alter insulin sensitivity both during and several hours after exercise, creating challenges for a closed-loop artificial pancreas. Predictive low glucose suspend (PLGS) algorithms are a first step toward an artificial pancreas, but few of these have been successfully applied to exercise. This study incorporates physical activity measurements from a combined accelerometer/heart rate monitor (HRM) to improve the performance of an existing PLGS algorithm at mitigating exercise-associated hypoglycemia in participants with type 1 diabetes. In all, 22 subjects with type 1 diabetes on insulin pump therapy were provided a combined accelerometer/HRM and (if not already using one) a continuous glucose monitor (CGM), then instructed to go about their everyday lives while wearing the devices. After the monitoring period, each subject's insulin pump, CGM, and accelerometer/HRM were downloaded and the data were used to augment an existing PLGS algorithm to incorporate activity. Using a computer simulator, the accelerometer-augmented algorithm was compared to the HRM-augmented algorithm to determine which was most effective at mitigating hypoglycemia. Mean length of monitoring was 4.9 days. Across all subjects, 11 061 CGM readings were recorded during the monitoring period. In the simulator analysis, the PLGS algorithm reduced hypoglycemia by 62%, compared to 71% and 74% reductions for the HRM-augmented and accelerometer-augmented algorithms, respectively; combined accelerometer and HRM augmentation provided a 76% reduction. In a simulated setting, the accelerometer-augmented pump suspension algorithm decreases the incidence of exercise-related hypoglycemia by a meaningful amount compared to the PLGS algorithm alone. Results also failed to justify the additional user burden of a HRM.

Exercise-related hypoglycemia in diabetes mellitus

Current recommendations are that people with Type 1 and Type 2 diabetes mellitus exercise regularly. However, in cases in which insulin or insulin secretagogues are used to manage diabetes, patients have an increased risk of developing hypoglycemia, which is amplified during and after exercise. Repeated episodes of hypoglycemia blunt autonomic nervous system, neuroendocrine and metabolic defenses (counter-regulatory responses) against subsequent episodes of falling blood glucose levels during exercise. Likewise, antecedent exercise blunts counter-regulatory responses to subsequent hypoglycemia. This can lead to a vicious cycle, by which each episode of either exercise or hypoglycemia further blunts counter-regulatory responses. Although contemporary insulin therapies cannot fully mimic physiologic changes in insulin secretion, people with diabetes have several management options to avoid hypoglycemia during and after exercise, including regularly monitoring blood glucose, reducing basal and/or bolus insulin, and consuming supplemental carbohydrates.

Exercise-Related Hypoglycemia in Type 2 Diabetes Treated With Oral Glucose-Lowering Medications

D.L. is a 58-year-old African-American man and business executive who was diagnosed with type 2 diabetes at the age of 52 years. In addition to diabetes, he has a history of hypertension and coronary artery disease (CAD). The diagnosis of CAD was made in late 2005, after D.L. experienced an episode of chest pressure and shortness of breath while at work. He consulted his primary care physician, who referred him for a cardiovascular evaluation to assess probable myocardial ischemia. The evaluation included a graded exercise test with thallium nuclear imaging, which revealed ischemic changes with exercise and reduced exercise tolerance. Coronary arteriography showed occlusion of the left anterior descending branch of the coronary artery (LAD), and angioplasty of the LAD with stent placement was performed. D.L. was referred to cardiac rehabilitation for an exercise and lifestyle change program. D.L. had completed 2 months of supervised exercise when he returned to his primary care physician after experiencing hypoglycemia both during and after exercise. Before this time, progression of his physical activity program had been excellent. He was exercising three mornings per week from 7:30 to 8:30 A.M. in the rehabilitation program and was walking 30-45 minutes on weekend days. Hypoglycemia was now a safety concern for both D.L. and the cardiac rehabilitation staff and was a barrier to further progression of his exercise program. On examination, D.L.'s height was 6 feet, 2 inches, and his weight was 215 lb (BMI 27.6 kg/m2). He had lost 15 lb in 2.5 months by consistently exercising and following …

Type 1 diabetes: exercise and hypoglycemia

The Diabetes Control and Complications Trial demonstrated that tight control of diabetes management greatly reduces the risk of microvascular complications of diabetes. Unfortunately, tight control of blood glucose can also result in hypoglycemia, especially in patients with type 1 diabetes mellitus (T1DM). It is now widely recognized that antecedent hypoglycemia can blunt neuroendocrine, autonomic nervous system (ANS), and metabolic counterregulatory responses to subsequent hypoglycemia. Thus, blunted counterregulatory defenses against falling plasma glucose levels are a major risk factor for hypoglycemia in people with diabetes. This risk is also complicated by a difference in responses between males and females. Because of the qualitative similarity of neuroendocrine, ANS, and metabolic responses to hypoglycemia and exercise, we developed studies to determine whether neuroendocrine and ANS counterregulatory dysfunction play a role in the pathogenesis of exercise-related hypoglycemia in T1DM. Results from these studies have shown that neuroendocrine (catecholamine and glucagon), ANS (muscle sympathetic nerve activity), and metabolic (lipolysis and glucose kinetics) responses are blunted during exercise after antecedent hypoglycemia, and that there is a sexual dimorphism in responses. Similarly, antecedent episodes of exercise can blunt counterregulatory responses during subsequent hypoglycemia, thereby creating reciprocal feed-forward vicious cycles that increase the risk of hypoglycemia during either stress.

Evidence for a vicious cycle of exercise and hypoglycemia in type 1 diabetes mellitus.

Exercise is a cornerstone of diabetes management as it aids in glycemic control, weight management, reducing blood pressure, and improving the quality of life of patients. Unfortunately, owing to the complexity and difficulties of regulating exogenous insulin in a physiologic manner during exercise, physical activity often results in hypoglycemia in patients with type 1 diabetes mellitus (type 1 DM). When glucose levels fall below threshold glycemic levels, neuroendocrine, autonomic nervous system (ANS), and metabolic glucose counterregulatory mechanisms are activated. These hypoglycemic counterregulatory mechanisms in type 1 DM can be blunted irreversibly by disease duration or by acute episodes of prior stress. These reduced (or absent) counterregulatory responses result in a threefold increase in severe hypoglycemia when intensive glycemic control is implemented in type 1 DM. Much recent work has been focused on determining the in vivo mechanisms responsible for causing the increased incidence of severe hypoglycemia in type 1 DM. Studies from several laboratories have demonstrated the role played by episodes of antecedent hypoglycemia in producing blunted glucose counterregulatory responses during subsequent exposures of hypoglycemia. Until recently, the mechanisms responsible for exercise related hypoglycemia in type 1 DM have been attributed to relative or absolute increases of insulin levels or incomplete glycogen repletion after physical activity. Owing to the qualitative similarity of neuroendocrine, ANS, and metabolic responses to hypoglycemia and exercise, we have hypothesized that neuroendocrine and ANS counterregulatory dysfunction may also play an important role in the pathogenesis of exercise-related hypoglycemia in type 1 DM. Vicious cycles can be created in type 1 DM, where an episode of hypoglycemia or exercise can feed forward to downregulate neuroendocrine and ANS responses to a subsequent episode of either stress, thereby creating further hypoglycemia. This article will review the recent work that has studied the contribution of counterregulatory dysfunction to exercise-induced hypoglycemia in type 1 DM.

Effect of Antecedent Hypoglycemia on Counterregulatory Responses to Subsequent Euglycemic Exercise in Type 1 Diabetes

Exercise-related hypoglycemia is common in intensively treated patients with type 1 diabetes. The underlying mechanisms are not clearly defined. In nondiabetic subjects, hypoglycemia blunts counterregulatory responses to subsequent exercise. It is unknown whether this also occurs in type 1 diabetes. Therefore, the goal of this study was to test the hypothesis that prior hypoglycemia could result in acute counterregulatory failure during subsequent exercise in type 1 diabetes. A total of 16 type 1 diabetic patients (8 men and 8 women, HbA(1c) 7.8 +/- 0.3%) were investigated during 90 min of euglycemic cycling exercise, following either two 2-h periods of previous-day hypoglycemia (2.9 mmol/l) or previous-day euglycemia. Patients' counterregulatory responses (circulating levels of counterregulatory hormones, intermediary metabolites, substrate flux via indirect calorimetry, tracer-determined glucose kinetics, and cardiovascular measurements) were comprehensively assessed during exercise. Identical euglycemia and basal insulin levels were successfully maintained during all exercise studies, regardless of blood glucose levels during the previous day. After resting euglycemia, patients displayed normal counterregulatory responses to exercise. Conversely, when identical exercise was repeated after hypoglycemia, the glucagon response to exercise was abolished, and the epinephrine, norepinephrine, cortisol, endogenous glucose production, and lipolytic responses were reduced by 40-80%. This resulted in a threefold increase in the amount of exogenous glucose needed to maintain euglycemia during exercise. Our results demonstrate that antecedent hypoglycemia, in type 1 diabetes, can produce acute counterregulatory failure during a subsequent episode of prolonged moderate-intensity exercise. The metabolic consequence of the blunted neuroendocrine and autonomic nervous system counterregulatory responses was an acute failure of endogenous glucose production to match the increased glucose requirements during exercise. These data indicate that counterregulatory failure may be a significant in vivo mechanism responsible for exercise-associated hypoglycemia in type 1 diabetes.

Effects of antecedent hypoglycemia on subsequent counterregulatory responses to exercise.

Antecedent hypoglycemia can blunt counterregulatory responses to subsequent hypoglycemia. It is uncertain, however, if prior hypoglycemia can blunt counterregulatory responses to other physiologic stresses. The aim of this study, therefore, was to determine whether antecedent hypoglycemia attenuates subsequent neuroendocrine and metabolic responses to exercise. Sixteen lean, healthy adults (eight men and eight women, ages 28+/-2 years, BMI 22+/-1 kg/m2, VO2max 43+/-3 ml x kg(-1) x min(-1)) were studied during 2-day protocols on two randomized occasions separated by 2 months. On day 1, subjects underwent morning and afternoon 2-h hyperinsulinemic (528+/-30 pmol/l) glucose clamp studies of 5.3+/-0.1 mmol/l (euglycemic control) or 2.9+/-0.1 mmol/l (hypoglycemic study). On day 2, subjects underwent 90 min of exercise on a static cycle ergometer at 80% of their anaerobic threshold (approximately 50% VO2max). Glycemia was equated during day 2 exercise studies via an exogenous glucose infusion. Day 1 hypoglycemia had significant effects on neuroendocrine and metabolic responses during day 2 exercise. The usual exercise-induced reduction in insulin, together with elevations of plasma epinephrine, norepinephrine, glucagon, growth hormone, pancreatic polypeptide, and cortisol levels, was significantly blunted after day 1 hypoglycemia (P<0.01). Commensurate with reduced neuroendocrine responses, key metabolic counterregulatory mechanisms of endogenous glucose production (EGP), lipolytic responses, and ketogenesis were also significantly attenuated (P<0.01) after day 1 hypoglycemia. Significantly greater rates of glucose infusion were required to maintain euglycemia during exercise after day 1 hypoglycemia compared with day 1 euglycemia (8.8+/-2.2 vs. 0.6+/-0.6 micromol x kg(-1) x min(-1); P<0.01). During the first 30 min of exercise, day 1 hypoglycemia had little effect on EGP, but during the latter 60 min of exercise, day 1 hypoglycemia was associated with a progressively smaller increase in EGP compared with day 1 euglycemia. Thus, by 90 min, the entire exercise-induced increment in EGP (8.8+/-1.1 micromol x kg(-1) x min(-1)) was abolished by day 1 hypoglycemia. We conclude that 1) antecedent hypoglycemia results in significant blunting of essential neuroendocrine (glucagon, insulin, catecholamines) and metabolic (endogenous glucose production, lipolysis, ketogenesis) responses to exercise; 2) antecedent hypoglycemia may play a role in the pathogenesis of exercise-related hypoglycemia in type 1 diabetic patients; and 3) antecedent hypoglycemia can blunt counterregulatory responses to other physiologic stresses in addition to hypoglycemia.