Impaired adrenergic response to prolonged exercise in type I diabetes

Rationale and methods for the Exercise for Type 1 Diabetes Education program: a pilot randomized controlled trial of an education program to support adults with type 1 diabetes mellitus (T1DM) to undertake exercise

Objective

Regular exercise in people with type 1 diabetes mellitus (T1DM) can result in considerable improvements in health and reduction in cardiovascular events and death. However, a large proportion of people with T1DM are not active. Fear of hypoglycemia and lack of knowledge on how to manage their diabetes are major barriers to exercise in people with T1DM, but few patients receive specific advice about how to adjust insulin and carbohydrate for activity. Furthermore, healthcare professionals (HCP) currently lack the knowledge to advise patients on how to manage their diabetes when active and would like formal training in exercise prescription for people with T1DM.

Research design and methods

This study is divided into two stages. The first stage develops an education program aimed to support people with T1DM to exercise using the Medical Research Council framework. The second stage is a pilot randomized controlled trial (RCT) that aims to collect the key variables to design a definitive trial to test the efficacy and cost-effectiveness of the education package. We aim to recruit 96 patients with T1DM at two UK hospitals.

Conclusions

This article outlines the protocol for a pilot RCT to develop a program of education that will support adults with T1DM to undertake safe and effective exercise. This is accompanied by training for HCPs to deliver this educational intervention. Successful completion of this program of work will address some of the barriers to exercise in adults with T1DM, and should facilitate an increase in exercise for this group of people.

Trial registration number

ISRCTN61403534.

Consequences of Type 1 and 2 Diabetes Mellitus on the Cardiovascular Regulation During Exercise: A Brief Review

INTRODUCTION

One challenging problem in patients suffering from Diabetes Mellitus (DM) is the elevate incidence of cardiovascular events. Exercise has been proved useful in reducing cardiovascular risks in these patients. However, both type 1 and 2 DM significantly affect the cardiovascular response during exercise. Therefore, on one side exercise is considered to be a valid therapeutic tool for DM, whereas on the other side during exercise these patients may experience troubles in the cardiovascular regulation.

BACKGROUND

Several impairments at central and at peripheral level have been reported during exercise in both types of DM. For example, sympathetic dysfunctions have been demonstrated in type 1 and 2 DM. Furthermore, impairments in hemodynamics have been often reported. The purpose of the present paper is to briefly review the latest data on the role played by type 1 and 2 DM in the cardiovascular regulation during dynamic exercise.

CONCLUSION

Hemodynamic dysfunctions may develop in both type 1 and 2 DM during exercise. However, these cardiovascular dys-regulations are different between the two kinds of diabetes.

Why should people with type 1 diabetes exercise regularly?

Plethoric evidence reminds of the protective effects of exercise against a number of health risks, across all ages, in the general population. The benefits of exercise for individuals with type 2 diabetes are indisputable. An in-depth understanding of energy metabolism has reasonably entailed exercise as a cornerstone in the lifestyle of almost all subjects with type 1 diabetes. Nevertheless, individuals with type 1 diabetes often fail in accomplishing exercise guidelines and they are less active than their peer without diabetes. Two major obstacles are feared by people with type 1 diabetes who wish to exercise regularly: management of blood glucose control and hypoglycemia. Nowadays, strategies, including glucose monitoring technology and insulin pump therapy, have significantly contributed to the participation in regular physical activity, and even in competitive sports, for people with type 1 diabetes. Novel modalities of training, like different intensity, interspersed exercise, are as well promising. The beneficial potential of exercise in type 1 diabetes is multi-faceted, and it has to be fully exploited because it goes beyond the insulin-mimetic action, possibly through immunomodulation.

Hypoglycemia during moderate intensity exercise reduces counterregulatory responses to subsequent hypoglycemia

Hypoglycemia, which occurs commonly during and following exercise in people with diabetes, is thought to be due to attenuated counterregulation in the setting of therapeutic insulin excess. To better understand the pathophysiology of counterregulation, we aimed to determine if dextrose administration to maintain euglycemia during moderate intensity exercise alters the attenuation of counterregulatory responses to subsequent hypoglycemia in healthy adults. Counterregulatory responses to hypoglycemia were assessed in 18 healthy adults after bed rest and following exercise with (n = 9) and without (n = 9) dextrose infusion. Responses were measured during a stepped euglycemic‐hypoglycemic clamp 24 h after either bed rest or two 90‐min bouts of exercise at 70% peak oxygen uptake. Hypoglycemia occurred during the second bout of exercise without dextrose infusion. Plasma glucagon and epinephrine responses to stepped hypoglycemia after antecedent exercise without dextrose infusion were significantly lower at the 45 mg/dL glycemic level compared to after bed rest. However, no attenuation of the counterregulatory responses to hypoglycemia was evident after antecedent exercise when dextrose was infused. This study suggests that the attenuation of the counterregulatory responses during hypoglycemia after exercise is likely due to the hypoglycemia that occurs during moderate prolonged exercise and not solely due to exercise or its intensity.

Altered hemodynamics during muscle metaboreflex in young type 1 diabetes patients

A reduction in catecholamine levels during exercise has been described in young subjects with type 1 diabetes mellitus (DM1). It has been suggested that type 1 diabetes per se is associated with the loss of sympathetic response before any clinical evidence. Considering that an increase in sympathetic drive is required for normal cardiovascular response to muscle metaboreflex, the aim of this study was to assess the hemodynamics during metaboreflex in DM1 patients. Impedance cardiography was used to measure hemodynamics during metaboreflex activation, obtained through postexercise ischemia in 14 DM1 patients and in 11 healthy controls (CTL). Principal results were: 1) blunted blood pressure response during metaboreflex was observed in DM1 patients compared with the CTL; 2) reduced capacity to increase systemic vascular resistance was also witnessed in DM1 subjects; 3) DM1 subjects reported higher stroke volumes as a consequence of reduced cardiac afterload compared with the CTL, which led to a more evident cardiac output response, which partially compensated for the lack of vasoconstriction. These facts suggest that cardiovascular regulation was altered in DM1 patients and that there was a reduced capacity to increase sympathetic tone, even in the absence of any overt clinical sign. The metaboreflex test appears to be a valid tool to detect early signs of this cardiovascular dysregulation.

Clinical management of the physically active patient with type 1 diabetes

The prevalence and incidence of type 1 diabetes continues to increase worldwide. Most patients with type 1 diabetes are young at the time of diagnosis and wish to continue leading a physically active life. Although regular exercise, insulin therapy, and proper nutrition are the cornerstone of treatment, there are considerable challenges in managing the active individual with type 1 diabetes. The current recommendation for diabetes management is intensive glycemic control for all patients when possible to help prevent secondary complications. Both insulin pump therapy and multiple daily injections are beneficial treatment options to lower average glucose levels; however, without continuous glucose monitoring, these treatment options typically increase the risk of hypoglycemia. In active patients with type 1 diabetes, the challenges of maintaining good glycemia are complicated by the inability to regulate insulin concentrations during and after exercise. Physiological and psychosocial factors during growth and maturation also provide additional challenges. This article highlights challenges and key strategies for diabetes management in the active individual with type 1 diabetes, including the application of the most recent diabetes technologies.

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.

Continuous glucose monitoring reveals delayed nocturnal hypoglycemia after intermittent high-intensity exercise in nontrained patients with type 1 diabetes

OBJECTIVE

Exercise is a cornerstone of diabetes therapy in type 1 diabetes mellitus (DMT1) patients. The type of exercise is important in determining the propensity to hypoglycemia. We assessed, by continuous glucose monitoring (CGM), the glucose profiles during and in the following 20h after a session of two different types of exercise.

RESEARCH DESIGN AND METHODS

Eight male volunteers with well-controlled DMT1 were studied. They underwent 30min of both intermittent high-intensity exercise (IHE) and moderate-intensity exercise (MOD) in random order. Expired air was recorded during exercise, while metabolic and hormonal determinations were performed before and for 120 min after exercises. The CGM system and activity monitor were applied for the subsequent 20h.

RESULTS

Blood glucose level declined during both type of exercise. At 150 min following the start of exercise, plasma glucose content was slightly higher after IHE. No changes were observed in plasma insulin concentration. A significant increase of norepinephrine concentration was noticed during IHE. Between midnight and 6:00 a.m. the glucose levels were significantly lower after IHE than those observed after MOD (area under the curve, 23.3 ± 3 vs. 16 ± 3 mg/dL/420 min [P = 0.04]; mean glycemia at 3 a.m., 225 ± 31 vs. 147 ± 17 mg/dL [P<0.05]). The number of hypoglycemic episodes after IHE was higher than that observed after MOD (seven vs. two [P<0.05]).

CONCLUSIONS

We demonstrate that (1) CGM is a useful approach in DMT1 patients who undergo an exercise program and (2) IHE is associated with delayed nocturnal hypoglycemia.

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.

Role of physical exercise in children and adolescents with diabetes mellitus

During the past 50 years several studies have underlined the central role of physical exercise in the management of patients with both type 1 and type 2 diabetes mellitus. The numerous benefits described in normal individuals who practise regular exercise have also been demonstrated in patients with diabetes who obtained significant physical and psychological advantages for the care of the underlying disease. Despite physical and psychological benefits, the occurrence of acute complications and some important effects on diabetes-related vascular complications may often discourage patients from participation in sports activities. However, even though adverse events may occur, exercise is still judged one of the most important components in the treatment of patients with diabetes. Thus, children, adolescents and young adults with diabetes must be educated on the metabolic changes occurring during physical activity in order to be able to acquire the ability to individually modulate their diet and insulin therapy before and after exercise. Appropriate education may allow a proper and correct approach to physical exercise.

Effect of differing antecedent hypoglycemia on counterregulatory responses to exercise in type 1 diabetes

Hypoglycemia frequently occurs during or after exercise in intensively treated patients with type 1 diabetes mellitus (T1DM), but the underlying mechanisms are not clear. In both diabetic and nondiabetic subjects, moderate hypoglycemia blunts counterregulatory responses to subsequent exercise, but it is unknown whether milder levels of hypoglycemia can exert similar effects in a dose-dependent fashion. This study was designed to test the hypothesis that prior hypoglycemia of differing depths induces acute counterregulatory failure of proportionally greater magnitude during subsequent exercise in T1DM. Twenty-two T1DM patients (11 males/11 females, HbA1c 8.0 +/- 0.3%) were studied during 90 min of euglycemic cycling exercise after two 2-h periods of previous day euglycemia or hypoglycemia of 3.9, 3.3, or 2.8 mmol/l (HYPO-3.9, HYPO-3.3, HYPO-2.8, respectively). Patients' counterregulatory responses (circulating levels of neuroendocrine hormones, intermediary metabolites, substrate flux, tracer-determined glucose kinetics, and cardiovascular measurements) were 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 day 1 euglycemia, patients displayed normal counterregulatory responses to exercise. Conversely, when identical exercise was performed after day 1 hypoglycemia of increasing depth, a progressively greater blunting of glucagon, catecholamine, cortisol, endogenous glucose production, and lipolytic responses to exercise was observed. This was paralleled by a graduated increase in the amount of exogenous glucose needed to maintain euglycemia during exercise. Our results demonstrate that acute counterregulatory failure during prolonged, moderate-intensity exercise may be induced in a dose-dependent fashion by differing depths of antecedent hypoglycemia starting at only 3.9 mmol/l in patients with T1DM.

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 prolonged exercise on subsequent counterregulatory responses to hypoglycemia

In the present study the hypothesis tested was that prior exercise may blunt counterregulatory responses to subsequent hypoglycemia. Healthy subjects [15 females (f)/15 males (m), age 27 +/- 1 yr, body mass index 22 +/- 1 kg/m(2), hemoglobin A(Ic) 5.6 +/- 0.5%] were studied during 2-day experiments. Day 1 involved either 90-min morning and afternoon cycle exercise at 50% maximal O2 uptake (VO2(max)) (priorEXE, n = 16, 8 m/8 f) or equivalent rest periods (priorREST, n = 14, 7 m/7 f). Day 2 consisted of a 2-h hypoglycemic clamp in all subjects. Endogenous glucose production (EGP) was measured using [3-3H]glucose. Muscle sympathetic nerve activity (MSNA) was measured using microneurography. Day 2 insulin (87 +/- 6 microU/ml) and plasma glucose levels (54 +/- 2 mg/dl) were equivalent after priorEXE and priorREST. Significant blunting (P < 0.01) of day 2 norepinephrine (-30 +/- 4%), epinephrine (-37 +/- 6%), glucagon (-60 +/- 4%), growth hormone (-61 +/- 5%), pancreatic polypeptide (-47 +/- 4%), and MSNA (-90 +/- 8%) responses to hypoglycemia occurred after priorEXE vs. priorREST. EGP during day 2 hypoglycemia was also suppressed significantly (P < 0.01) after priorEXE compared with priorREST. In summary, two bouts of exercise (90 min at 50% VO2(max)) significantly reduced glucagon, catecholamines, growth hormone, pancreatic polypeptide, and EGP responses to subsequent hypoglycemia. We conclude that, in normal humans, antecedent prolonged moderate exercise blunts neuroendocrine and metabolic counterregulatory responses to subsequent hypoglycemia.

Autonomic and endothelial dysfunction in experimental diabetes

The effect of streptozotocin induced diabetes on autonomic regulation of heart rate and endothelial function was examined in Sprague-Dawley rats. Weanling rats (3-4 weeks of age) of either sex were randomly assigned to a non-diabetic (male 5, female 6) or diabetic (male 4, female 5). Diabetes was induced with a single intraperitoneal (IP) injection of streptozotocin (STZ, 100 mg/kg). Nondiabetic rats received an IP injection of saline. Eight weeks after injection, rats were chronically instrumented with a left jugular venous catheter and a left carotid arterial catheter. After recovery (5 days) cardiac sympathetic tonus, parasympathetic tonus and intrinsic heart rate were determined. On an alternative day, the pressor response to nitric oxide synthase inhibition (NOS-X) was determined in areflexic rats. Cardiac sympathetic tonus (72 +/- 13 vs. 41 +/- 7), parasympathetic tonus (-51 +/- 10 vs. -22 +/- 7), and intrinsic heart rate (368 +/- 6 vs. 292 +/- 9), were reduced in diabetic rats. Furthermore, diabetic rats had a smaller pressor response (A33 +/- 7 vs. A66 +/- 5) to NOS-X. These results document impaired autonomic control of heart rate and endothelial dysfunction in 8-week streptozotocin induced diabetic rats.

Cardiac and plasma catecholamine responses to exercise in patients with type 2 diabetes: prognostic implications for cardiac-cerebrovascular events

BACKGROUND

Patients with diabetes mellitus have an altered exercise plasma catecholamine response, which may be related to the abnormal sympathoadrenal function and autonomic neuropathy. Presence of autonomic neuropathy is associated with poor prognosis, but relationship between exercise plasma catecholamine and prognosis has not been investigated. This study determined if altered plasma catecholamine response to exercise was associated with cardiac-cerebrovascular events.

METHODS

Forty patients with type 2 diabetes without apparent macrovascular complications and 30 control subjects performed treadmill exercise with serial measurements of plasma norepinephrine and epinephrine. Clinical, exercise, and catecholaminergic variables considered relevant to the cardiac-cerebrovascular events were examined by Cox regression model. Analysis of 24-hour heart rate variability was performed in a subgroup of patients.

RESULTS

During 7.2 years, 8 patients, but no control subjects, had events (3 myocardial and 5 cerebral infarctions). Compared with Event(-) patients, Event(+) patients had: (1) orthostatic hypotension; (2) lower peak exercise heart rate; (3) lower plasma norepinephrine immediately after exercise; and (4) lower plasma epinephrine at peak exercise. High frequency components in heart rate variability analysis were diminished in Event(+) patients. Multivariate analysis showed that peak heart rate (P = 0.04) and plasma epinephrine at peak exercise (P = 0.03) were independent predictors of subsequent events.

CONCLUSIONS

These data suggest that chronotropic incompetence and lower plasma epinephrine response to exercise are associated with high risk of cardiac-cerebrovascular events in patients with type 2 diabetes.

Diabetes and exercise

Exercise is frequently recommended in the management of type 1 and 2 diabetes mellitus and can improve glucose uptake by increasing insulin sensitivity and lowering body adiposity. Both alone and when combined with diet and drug therapy, physical activity can result in improvements in glycaemic control in type 2 diabetes. In addition, exercise can also help to prevent the onset of type 2 diabetes, in particular in those at higher risk, and has an important role in reducing the significant worldwide burden of this type of diabetes. Recent studies have improved our understanding of the acute and long term physiological benefits of physical activity, although the precise duration, intensity, and type of exercise have yet to be fully elucidated. However, in type 1 diabetes, the expected improvements in glycaemic control with exercise have not been clearly established. Instead significant physical and psychological benefits of exercise can be achieved while careful education, screening, and planning allow the metabolic, microvascular, and macrovascular risks to be predicted and diminished.

Interaction of exercise, insulin, and hypoglycemia studied using euglycemic and hypoglycemic insulin clamps

Hyperinsulinemic euglycemic and hypoglycemic clamps were used to study the interaction of exercise, insulin, and hypoglycemia at rest and during exercise in the dog. Sampling (artery and portal, hepatic, and iliac veins) and infusion (vena cava) catheters and a flow probe (external iliac artery) were implanted surgically >16 days before study. After an 18-h fast and an 80-min tracer equilibration period, dogs were studied in the basal state (t = -40 to 0 min) and during a moderate treadmill exercise (t = 0-150 min) period or an equivalent duration sedentary period. Insulin was infused at 1 mU x kg(-1) x min(-1) from t = 0-150 min. In one group of sedentary (n = 7) and one group of exercised (n = 6) dogs, glucose was clamped at basal during the insulin infusion. In another group of sedentary (n = 6) and another group of exercised (n = 6) dogs, arterial glucose was clamped at hypoglycemic levels (approximately 65 mg/dl) during the insulin infusion. Arteriovenous difference and isotopic ([3-(3)H]glucose, [U-(14)C]glucose) techniques were used to assess glucose metabolism. Insulin levels were approximately 40 microU/ml in all groups. Data show that 1) counterregulatory hormone (glucagon, catecholamines, and cortisol) responses to exercise and hypoglycemia combined are synergistically higher than the response to either stimulus alone; 2) exercise-induced increases in insulin action are negated during hypoglycemia by the counterregulatory response; 3) decreased need for exogenous glucose during hypoglycemic compared with euglycemic exercise is due to stimulation of endogenous glucose production, which accounts for approximately 30% of the decrease, and reduction of glucose utilization, which accounts for approximately 70%; and 4) insulin-stimulated nonoxidative glucose metabolism is unaffected by exercise or hypoglycemia, whereas insulin-stimulated oxidative glucose metabolism is selectively increased by exercise and decreased by hypoglycemia. In conclusion, the marked rise in insulin action during exercise is matched, under insulin-induced hypoglycemic conditions, by an equally profound increase in counterregulation. The effectiveness of the potent insulin counterregulatory response may be important in decreasing the magnitude and frequency of exercise-induced hypoglycemia.