Serum HbA1c levels and exercise capacity in diabetic patients

Distinct effects of type 2 diabetes and obesity on cardiopulmonary performance

AIM

Effort intolerance is frequent in patients with overweight/obesity and/or type 2 diabetes (T2D) free from cardiac and respiratory disease. We sought to quantify the independent effects of T2D and body mass index (BMI) on cardiopulmonary capacity and gain insights on the possible pathophysiology by case-control and regression analyses.

METHODS

Patients at high/moderate cardiovascular risk, with or without T2D, underwent spirometry and combined echocardiography-cardiopulmonary exercise test as part of their clinical workup. Subjects with evidence of cardiopulmonary disease were excluded. The effects of T2D and obesity were estimated by multivariable models accounting for known/potential confounders and the major pathophysiological determinants of oxygen uptake at peak exercise (VO2peak ) normalized for fat-free mass (FFM).

RESULTS

In total, 109 patients with T2D and 97 controls were included in the analysis. The two groups had similar demographic and anthropometric characteristics except for higher BMI in T2D (28.6 ± 4.6 vs. 26.3 ± 4.4 kg/m2 , p = .0003) but comparable FFM. Patients with T2D achieved lower VO2peak than controls (18.5 ± 4.4 vs. 21.7 ± 8.3 ml/min/kg, p = .0006). Subclinical cardiovascular dysfunctions were observed in T2D: concentric left ventricular remodelling, autonomic dysfunction, systolic dysfunction and reduced systolic reserve. After accounting for confounders and major determinants of VO2peakFFM , T2D still displayed reduced VO2peak by 1.0 (-1.7/-0.3) ml/min/kgFFM , p = .0089, while the effect of BMI [-0.2 (-0.3/0.1) ml/min/kgFFM , p = .06 per unit increase], was largely explained by a combination of chronotropic incompetence, reduced peripheral oxygen extraction, impaired systolic reserve and ventilatory (in)efficiency.

CONCLUSIONS

T2D is an independent negative determinant of VO2peak whose effect is additive to other pathophysiological determinants of oxygen uptake, including BMI.

The AGE-RAGE Axis and the Pathophysiology of Multimorbidity in COPD

Chronic obstructive pulmonary disease (COPD) is a disease of the airways and lungs due to an enhanced inflammatory response, commonly caused by cigarette smoking. Patients with COPD are often multimorbid, as they commonly suffer from multiple chronic (inflammatory) conditions. This intensifies the burden of individual diseases, negatively affects quality of life, and complicates disease management. COPD and comorbidities share genetic and lifestyle-related risk factors and pathobiological mechanisms, including chronic inflammation and oxidative stress. The receptor for advanced glycation end products (RAGE) is an important driver of chronic inflammation. Advanced glycation end products (AGEs) are RAGE ligands that accumulate due to aging, inflammation, oxidative stress, and carbohydrate metabolism. AGEs cause further inflammation and oxidative stress through RAGE, but also through RAGE-independent mechanisms. This review describes the complexity of RAGE signaling and the causes of AGE accumulation, followed by a comprehensive overview of alterations reported on AGEs and RAGE in COPD and in important co-morbidities. Furthermore, it describes the mechanisms by which AGEs and RAGE contribute to the pathophysiology of individual disease conditions and how they execute crosstalk between organ systems. A section on therapeutic strategies that target AGEs and RAGE and could alleviate patients from multimorbid conditions using single therapeutics concludes this review.

Type 2 diabetes and reduced exercise tolerance: a review of the literature through an integrated physiology approach

The association between type 2 diabetes mellitus (T2DM) and heart failure (HF) is well established. Early in the course of the diabetic disease, some degree of impaired exercise capacity (a powerful marker of health status with prognostic value) can be frequently highlighted in otherwise asymptomatic T2DM subjects. However, the literature is quite heterogeneous, and the underlying pathophysiologic mechanisms are far from clear. Imaging-cardiopulmonary exercise testing (CPET) is a non-invasive, provocative test providing a multi-variable assessment of pulmonary, cardiovascular, muscular, and cellular oxidative systems during exercise, capable of offering unique integrated pathophysiological information. With this review we aimed at defying the cardiorespiratory alterations revealed through imaging-CPET that appear specific of T2DM subjects without overt cardiovascular or pulmonary disease. In synthesis, there is compelling evidence indicating a reduction of peak workload, peak oxygen assumption, oxygen pulse, as well as ventilatory efficiency. On the contrary, evidence remains inconclusive about reduced peripheral oxygen extraction, impaired heart rate adjustment, and lower anaerobic threshold, compared to non-diabetic subjects. Based on the multiparametric evaluation provided by imaging-CPET, a dissection and a hierarchy of the underlying mechanisms can be obtained. Here we propose four possible integrated pathophysiological mechanisms, namely myocardiogenic, myogenic, vasculogenic and neurogenic. While each hypothesis alone can potentially explain the majority of the CPET alterations observed, seemingly different combinations exist in any given subject. Finally, a discussion on the effects -and on the physiological mechanisms-of physical activity and exercise training on oxygen uptake in T2DM subjects is also offered. The understanding of the early alterations in the cardiopulmonary response that are specific of T2DM would allow the early identification of those at a higher risk of developing HF and possibly help to understand the pathophysiological link between T2DM and HF.

Repeated High-Intensity Cycling Performance Is Unaffected by Timing of Carbohydrate Ingestion

Shei, R-J, Paris, HL, Beck, CP, Chapman, RF, and Mickleborough, TD. Repeated high-intensity cycling performance is unaffected by timing of carbohydrate ingestion. J Strength Cond Res 32(8): 2243-2249, 2018-To determine whether carbohydrate (CHO) feeding taken immediately before, early, or late in a series of high-intensity cycling exercises affected cycling performance. A total of 16 trained, male cyclists (>6 hours postprandial) performed 3-, 4-km cycling time trials (TT1, TT2, and TT3) separated by 15 minutes of active recovery on 4 separate occasions. Carbohydrate feeding (80 g) was given either before TT1 (PRE1), before TT2 (PRE2), before TT3 (PRE3), or not at all (control, CTL). Treatment order was randomized. Sweet placebo was given before the other TTs. Blood glucose (BG) concentration was measured before each trial. Mean power output (Pmean) and time to completion (TTC) were recorded. Pmean was higher in TT1 compared with TT2 (p = 0.001) and TT3 (p = 0.004) in all conditions, but no differences were observed between treatments. Time to completion was lower in TT1 compared with TT2 (p = 0.01), but no other differences in TTC (within or between treatments) were observed. Within CTL and PRE1, BG did not differ between TT1, TT2, and TT3. In PRE2, BG was significantly higher in TT2 compared with TT1 (p = 0.006), in TT3 compared with TT1 (p = 0.001), and in TT3 compared with TT2 (p = 0.01). In PRE3, BG was significantly higher in TT3 compared with TT1 and TT2 (p = 0.001 for both). Given that performance was not influenced by the timing of CHO ingestion, athletes engaging in repeated, high-intensity cycling exercise do not need to ingest CHO before- or between-exercise bouts; furthermore, athletes should refrain from ingesting CHO between bouts if they wish to avoid a rise in BG.

Impact of type 2 diabetes on cardiorespiratory function and exercise performance

The aim of this study was to examine the impact of well‐controlled uncomplicated type 2 diabetes (T2D) on exercise performance. Ten obese sedentary men with T2D and nine control participants without diabetes matched for age, sex, and body mass index were recruited. Anthropometric characteristics, blood samples, resting cardiac, and pulmonary functions and maximal oxygen uptake (VO_2max) and ventilatory threshold were measured on a first visit. On the four subsequent visits, participants (diabetics: n = 6; controls: n = 7) performed step transitions (6 min) of moderate‐intensity exercise on an upright cycle ergometer from unloaded pedaling to 80% of ventilatory threshold. VO₂ (τVO₂) and HR (τHR) kinetics were characterized with a mono‐exponential model. VO_2max (27.0 ± 3.4 vs. 26.7 ± 5.0 mL kg⁻¹ min⁻¹; P = 0.85), τVO₂ (43 ± 6 vs. 43 ± 10 sec; P = 0.73), and τHR (42 ± 17 vs. 43 ± 13 sec; P = 0.94) were similar between diabetics and controls respectively. The remaining variables were also similar between groups, with the exception of lower maximal systolic blood pressure in diabetics (P = 0.047). These results suggest that well‐controlled T2D is not associated with a reduction in VO_2max or slower τVO₂ and τHR.

[Predictors of changes in functional capacity on a cardiac rehabilitation program]

INTRODUCTION

The effectiveness of cardiac rehabilitation programs (CRP) strongly influences the recovery of functional capacity (FC), resulting in improved prognosis and survival.

OBJECTIVE

To determine the cardiovascular risk factors that predict changes in FC in patients on CRP.

METHODS

We performed a cross-sectional descriptive retrospective study of patients who began a CRP between January 2008 and December 2013. The dependent variable was changes in FC estimated in metabolic equivalents (METs) achieved in stress testing at the beginning and end of the phase II program. The independent variables were age, gender, dyslipidemia, diabetes, smoking, body mass index, physical activity level and reason for referral to the CRP.

RESULTS

The sample included 1399 patients, of whom 1125 (80.4%) completed the program. FC improved in most patients (93%), with a mean gain of 1.45 ± 1.19 METs. Patients aged 45 -65 and over 65 years achieved a greater increase in FC compared with other age groups. Patients admitted to the CRP after coronary artery bypass graft surgery obtained a greater improvement in FC compared to patients with acute coronary syndrome. Non-diabetic patients benefited more than diabetic patients. No significant differences were seen between the groups in the other variables.

CONCLUSION

This study highlights the need for new and individualized approaches in certain subgroups of patients on CRP.

Impact of diabetes and diastolic dysfunction on exercise capacity in normotensive patients without coronary artery disease

OBJECTIVE

The aim of this study was to determine the impact of diabetes and diastolic dysfunction on exercise capacity in asymptomatic, normotensive patients with type 2 diabetes without coronary artery disease.

METHODS

A total of 43 type 2 diabetes patients (age: 50 ± 5 years) and 20 healthy controls (age: 48 ± 4 years) were enrolled. Diastolic function was investigated by conventional pulsed-wave (PW) Doppler and tissue Doppler imaging (TDI). Exercise capacity was evaluated with cardiopulmonary exercise testing (CPET).

RESULTS

In patients with type 2 diabetes, increase in resting heart rate (HR-rest) (p = 0.013), decrease in maximum heart rate during exercise (HR-max) (p < 0.001) and exercise time (p < 0.001) compared with controls were significant. Patients had significantly increased minute ventilation volume (VE)/maximum carbon dioxide discharge (VCO2) ratio (p < 0.001), decreased maximum oxygen consumption (VO2-max) (p < 0.001), oxygen consumption at anaerobic threshold (VO2-an) (p < 0.001) and maximum carbon dioxide discharge (VCO2) (p < 0.001) compared to controls indicating significantly reduced exercise capacity. HbA1c was inversely correlated with VO2-max (r = -0.456, p < 0.01) independent of the absence or presence of mild diastolic dysfunction.

CONCLUSION

Exercise capacity was found to be significantly decreased in normotensive patients with type 2 diabetes without coronary artery disease, and this decrease was independent of diastolic dysfunction.

Relationships between cardiorespiratory fitness, metabolic control, and fat distribution in type 2 diabetes subjects

Factors contributing to the reduced cardiorespiratory fitness typical of sedentary subjects with type 2 diabetes are still largely unknown. In this study, we assessed the relationships between cardiorespiratory fitness and abdominal and skeletal muscle fat content in 39 untrained type 2 diabetes subjects, 27 males and 12 females (mean ± SD age 56.5 ± 7.3 year, BMI 29.4 ± 4.7 kg/m(2)). Peak oxygen uptake (VO2peak) and ventilatory threshold (VO2VT) were assessed by maximal cycle ergometer exercise test, insulin sensitivity by euglycemic-hyperinsulinemic clamp, and body composition by dual-energy X-ray absorptiometry. Magnetic resonance imaging was used to evaluate visceral, total subcutaneous (SAT), superficial (SSAT) and deep sub-depots of subcutaneous abdominal adipose tissue, and sagittal abdominal diameter (SAD), as well as femoral quadriceps skeletal muscle fat content. In univariate analysis, both VO2peak and VO2VT were inversely associated with BMI, total fat mass, SAT, SSAT, and sagittal abdominal diameter. VO2peak was also inversely associated with skeletal muscle fat content. A significant direct association was observed between VO2VT and insulin sensitivity. No associations between cardiorespiratory fitness parameters and metabolic profile data were found. In multivariable regression analysis, after adjusting for age and gender, VO2peak was independently predicted by higher HDL cholesterol, and lower SAD and skeletal muscle fat content (R (2) = 0.64, p < 0.001), whereas VO2VT was predicted only by sagittal abdominal diameter (R (2) = 0.48, p = 0.025). In conclusion, in untrained type 2 diabetes subjects, peak oxygen uptake is associated with sagittal abdominal diameter, skeletal muscle fat content, and HDL cholesterol levels. Future research should target these features in prospective intervention studies.

Molecular effects of advanced glycation end products on cell signalling pathways, ageing and pathophysiology

Advanced glycation end-products (AGEs) are a heterogeneous group of compounds formed by the Maillard chemical process of non- enzymatic glycation of free amino groups of proteins, lipids and nucleic acids. This chemical modification of biomolecules is triggered by endogeneous hyperglycaemic or oxidative stress-related processes. Additionally, AGEs can derive from exogenous, mostly diet-related, sources. Considering that AGE accumulation in tissues correlates with ageing and is a hallmark in several age-related diseases it is not surprising that the role of AGEs in ageing and pathology has become increasingly evident. The receptor for AGEs (RAGE) is a single transmembrane protein being expressed in a wide variety of human cells. RAGE binds a broad repertoire of extracellular ligands and mediates responses to stress conditions by activating multiple signal transduction pathways being mostly responsible for acute and/or chronic inflammation. RAGE activation has been implicated in ageing as well as in a number of age-related diseases, including atherosclerosis, neurodegeneration, arthritis, stoke, diabetes and cancer. Here we present a synopsis of findings that relate to AGEs-reported implication in cell signalling pathways and ageing, as well as in pathology. Potential implications and opportunities for translational research and the development of new therapies are also discussed.

Non-enzymatic post-translational protein modifications and proteostasis network deregulation in carcinogenesis

Organisms are constantly challenged by stressors and thus the maintenance of biomolecules functionality is essential for the assurance of cellular homeostasis. Proteins carry out the vast majority of cellular functions by mostly participating in multimeric protein assemblies that operate as protein machines. Cells have evolved a complex proteome quality control network for the rescue, when possible, or the degradation of damaged polypeptides. Nevertheless, despite these proteostasis ensuring mechanisms, new protein synthesis, and the replication-mediated dilution of proteome damage in mitotic cells, the gradual accumulation of stressors during aging (or due to lifestyle) results in increasingly damaged proteome. Non-enzymatic post-translational protein modifications mostly arise by unbalanced redox homeostasis and/or high glucose levels and may cause disruption of proteostasis as they can alter protein function. This outcome may then increase genomic instability due to reduced fidelity in processes like DNA replication or repair. Herein, we present a synopsis of the major non-enzymatic post-translation protein modifications and of the proteostasis network deregulation in carcinogenesis. We propose that activation of the proteostasis ensuring mechanisms in premalignant cells has tumor-preventive effects, whereas considering that over-activation of these mechanisms represents a hallmark of advanced tumors, their inhibition provides a strategy for the development of anti-tumor therapies. This article is part of a Special Issue entitled: Posttranslational Protein modifications in biology and Medicine.

Exercise capacity in relation to body fat distribution and muscle fibre distribution in elderly male subjects with impaired glucose tolerance, type 2 diabetes and matched controls

BACKGROUND

The aim of this study was to examine the impact of insulin sensitivity and muscle fibre composition to exercise capacity in individuals with type 2 diabetes (T2D), impaired glucose tolerance (IGT) and normal glucose tolerance (NGT).

METHODS

Thirty-nine male patients with T2D, 44 male subjects with IGT and 58 subjects with NGT matched for age, weight and body mass index (BMI) participated in the study. Insulin sensitivity was obtained with hyperinsulinemic-euglycemic clamps, muscle fibre distribution with a biopsy and exercise capacity from an incremental exercise test. Anthropometric measurements as height, weight, waist and hip circumference were performed.

RESULTS

There were small differences between groups in waist hip ratio (WHR) with significance attained between NGT and T2D. There was a progressive reduction in exercise capacity, both expressed as VO(2peak) and work rate from subjects with NGT to IGT to T2D. Multiple regression analysis with VO(2peak) as dependent variable showed insulin sensitivity to be the most important factor followed by Type I fibres. WHR and capillary density also influenced the variance of VO(2peak).

CONCLUSION

Exercise capacity is independently related to insulin sensitivity, muscle fibre composition and WHR in subjects with NGT, IGT and T2D who are matched for age and BMI.

Continuous, non-invasive measurement of the haemodynamic response to submaximal exercise in patients with diabetes mellitus: evidence of impaired cardiac reserve and peripheral vascular response

BACKGROUND

Reduced exercise capacity in diabetics has been attributed to limitations in cardiac function and microvascular dysfunction leading to impaired oxygen supply and nutritive perfusion to exercising muscles.

OBJECTIVE

To study changes in cardiac function and microvascular utilisation during exercise in diabetic individuals compared to age-matched controls.

METHODS

Diabetics with glycosylated haemoglobin (HbA(1c)) < 8 (n = 31), diabetics with HbA(1c) > or = 8 (n = 38) and age-matched non-diabetic controls (n = 32) performed exercise at 50 W for 10 minutes followed by recovery, with continuous monitoring of cardiac function by impedance cardiography and regional flow and oxygen saturation by laser Doppler and white light spectroscopy.

RESULTS

In the diabetics, cardiac reserve during exercise and cardiac overshoot during recovery are significantly reduced because of reduction in capacity to increase stroke volume. Regional flow to the exercising muscle is reduced and there is also disproportionately greater desaturation of the regional flow. Abnormalities in cardiac function and regional perfusion are related to the severity of diabetes.

CONCLUSION

Cardiac response to exercise is attenuated significantly in diabetic individuals. Simultaneously, there is impairment in the regional distribution. These changes could be the harbinger of reduced exercise capacity in diabetics.

Supervised exercise in patients with impaired fasting glucose: impact on exercise capacity

OBJECTIVE

To compare the effects of counseling alone with that of additional participation in supervised training courses on exercise capacity in patients with impaired fasting glucose.

DESIGN

Randomized, controlled intervention trial using a nested cohort approach.

SETTING

Primary care centers in western Austria.

PATIENTS

Thirty-six patients with impaired fasting glucose (16 males, 20 females; mean age, 57.5 +/- 6.9 years).

INTERVENTIONS

Participants of both groups were instructed about the preventive effectiveness of changing their lifestyle, especially losing weight and increasing physical activity. One group had additionally been offered supervised, progressive, individually tailored aerobic exercise programs for 1 hour twice a week.

MAIN OUTCOME MEASURES

Changes in the levels of exercise capacity, body mass, and fasting blood glucose.

RESULTS

The subjects with supervised exercise participated in this program for 1.8 hours (+/- 0.3) per week over 12 months. Supervised exercise was sufficient to maintain exercise capacity, whereas counseling alone was not (+4.4% versus -6.9%; P = 0.01). After the 12-month intervention period, body mass was reduced in the supervised exercise group (-3.0%) compared with the counseling alone group (+1.0%) (P = 0.03) and fasting plasma glucose levels had similarly improved by counseling for adequate lifestyle changes alone (-8.2%) and in combination with supervised exercise (-6.0%).

CONCLUSION

In contrast to counseling alone, 2 sessions of supervised training per week, besides the self-chosen physical activity and nutritional measures, are sufficient to maintain exercise capacity in patients with impaired fasting glucose.

Long-term effects of antihypertensive drugs on the risk of new-onset diabetes in elderly Taiwanese hypertensives

Antihypertensive drugs have been linked to new-onset diabetes (NOD); however, the effects of these drugs on the development of NOD in elderly Taiwanese hypertensive patients have not been well determined. We examined the association between antihypertensive drug therapy and the risk of NOD in a population-based study. The sample consisted of 8,638 elderly hypertensive patients. The data were obtained from claim forms provided to the central region branch of the Bureau of National Health Insurance in Taiwan from January 2001 to December 2006. Prescriptions for antihypertensive drugs before the index date were retrieved from a prescription database. We estimated the odds ratios (ORs) of NOD associated with antihypertensive drug use; nondiabetic subjects served as the reference group. The risk of NOD was higher among users of diuretics (OR, 1.12; 95% confidence interval [CI], 1.04-1.21), and beta-blockers (OR, 1.11; 95% CI, 1.02-1.20) than among nonusers. Patients who take angiotensin-converting enzyme (ACE) inhibitors (OR, 0.90; 95% CI, 0.82-0.98) or alpha-blockers (OR, 0.88; 95% CI, 0.78-0.99) are at a lower risk of developing NOD than nonusers. Angiotensin receptor blockers, calcium channel blockers, and vasodilators were not associated with risk of NOD. The results suggest that elderly hypertensive patients who take ACE inhibitors or alpha-blockers are at lower risk of NOD. Diuretics and beta-blockers were associated with a significant increase in the risk of NOD.

Impaired exercise capacity in diabetic patients after coronary bypass surgery: effects of diastolic and endothelial function

OBJECTIVES

The aims of this study were to clarify the influence of cardiac diastolic and peripheral vascular function on the exercise capacity of patients with coronary bypass surgery (CABG) and diabetes mellitus (DM) by tissue Doppler imaging (TDI) and flow-mediated vasodilatation (FMD), and to investigate interrelations between exercise capacity and LV diastolic function, endothelial function and biochemical parameters.

METHODS

We analyzed the exercise capacity, TDI at the mitral annulus and FMD in 51 uncomplicated first-time CABG survivors (23 DM) at an average interval of 21.6 +/- 12.2 months after surgery.

RESULTS

Diabetics had lower E', A', VO(2)peak, (a-v)O(2) difference, and higher E/E' ratios (p < 0.05) than non-DM patients, but not FMD (p = 0.17). The A and E/E' ratios correlated negatively with VO(2)peak after age adjustment (r = -0.336, p = 0.024). In addition, HbA(1c), and triglyceride also correlated negatively with VO(2)peak (r = -0.377, -0.307, respectively, p < 0.05).

CONCLUSIONS

Diabetics after CABG had more advanced diastolic dysfunction and oxygen extraction impairment than non-DM. It suggests these factors could contribute to lower exercise capacity, risk of developing heart failure despite preserved systolic function and poorer long-term survival of diabetic patients after CABG.

Impact of diabetes, chronic heart failure, congenital heart disease and chronic obstructive pulmonary disease on acute and chronic exercise responses

Several chronic diseases are known to negatively affect the ability of an individual to perform exercise. However, the altered exercise capacity observed in these patients is not solely associated with the heart and lungs dysfunction. Exercise has also been shown to play an important role in the management of several pathologies encountered in the fields of cardiology and pneumology. Studies conducted in our institution regarding the influence of diabetes, chronic heart failure, congenital heart disease and chronic pulmonary obstructive disease on the acute and chronic exercise responses, along with the beneficial effects of exercise training in these populations, are reviewed.

Influence of glycemic control on pulmonary function and heart rate in response to exercise in subjects with type 2 diabetes mellitus

Conflicting results exist regarding the impact of glycemic control on peak oxygen uptake (VO2peak) in subjects with type 2 diabetes mellitus. The influence of glycemic control on submaximal oxygen uptake (VO2) in these subjects is unknown. The aim of this study was to evaluate the impact of fasting blood glucose (FBG) (short-term glycemic control) and glycated hemoglobin (HbA1c) (long-term glycemic control) on submaximal VO2 and VO2peak during exercise in subjects with type 2 diabetes mellitus without cardiovascular disease. FBG and HbA1c levels and exercise tolerance in 30 sedentary men with type 2 diabetes mellitus treated with oral hypoglycemic agents and/or diet were evaluated. VO2, carbon dioxide production (VCO2), heart rate, pulmonary ventilation (VE), and the respiratory exchange ratio (RER) were measured throughout the exercise protocol. Subjects were separated into 2 groups of the same age, weight, and body mass index according to median FBG and HbA1c levels (6.5 mmol/L and 6.1%, respectively). Per protocol design, there was a significant difference in FBG and HbA1c levels (P < .001), but not for age, weight, or body mass index. There was no significant difference in peak exercise parameters between the 2 groups according to median FBG or median HbA1c levels. However, the subjects with elevated HbA1c level had lower submaximal V e throughout the exercise protocol (P < .03), and the subjects with elevated FBG concentration had a blunted heart rate pattern during submaximal exercise (P < .03). Although relatively small abnormalities in the control of glycemia do not affect VO2peak in subjects with type 2 diabetes mellitus without cardiovascular disease, they may influence pulmonary function and the chronotropic response during submaximal exercise in these subjects.

Fasting blood glucose levels are related to exercise capacity in patients with coronary artery disease

BACKGROUND AND AIM

Previous studies have demonstrated reduced exercise capacity in patients with diabetes mellitus. This study evaluated the relationship between fasting blood glucose (FBG) levels and exercise capacity in patients with coronary artery disease (CAD).

METHODS

We evaluated 986 consecutive patients with CAD referred for bicycle spiroergometry combined with gated myocardial perfusion imaging. Maximum oxygen consumption (VO2max) and maximal watts were measured. Patients were divided into 4 FBG categories: < 100 mg/dL (n = 611), 100 to 109 mg/dL (n = 144), 110 to 125 mg/dL (n = 102), and > or = 126 mg/dL (n = 129). Differences in clinical characteristics, exercise hemodynamics, perfusion imaging, and univariate as well as multivariate predictors of exercise capacity were determined.

RESULTS

Maximal watts and VO2max were significantly lower (P < .0001) in patients with higher FBG levels and were related to FBG values in univariate and multivariate analyses. Left ventricular volumes and ejection fractions did not differ between the FBG categories. Myocardial perfusion imaging showed a comparable degree of ischemia in the 4 FBG groups. However, patients with higher FBG levels had higher heart rate and blood pressure values at rest resulting in a higher rate-pressure product (values in the 4 FBG groups 8299 +/- 2051, 8733 +/- 2008, 9558 +/- 2583, and 9588 +/- 2468 beat/min x mm Hg, P < .0001), suggesting increased myocardial oxygen consumption per unit time at rest.

CONCLUSION

Exercise capacity in patients with CAD is related to FBG levels. Patients with impaired fasting glucose or an FBG level > or = 126 mg/dL reached lower peak watts and lower VO2max values. This could be attributed to a higher myocardial oxygen consumption per unit time at rest and the inability to adapt their coronary flow adequately to higher metabolic demands during maximal exercise.

Decreased isometric muscle strength after acute hyperglycaemia in Type 1 diabetic patients

AIMS

Fatigue is a common complaint in diabetic patients during periods of hyperglycaemia. To test whether muscle performance is reduced during acute hyperglycaemia, diabetic patients were studied whilst performing maximal isokinetic and isometric contractions.

METHODS

In this double-blind placebo controlled study, maximal isometric and isokinetic muscle strength was determined in seven Type 1 diabetic patients during normo- and hyperglycaemia using a hyperglycaemic clamp technique. On two separate days, maximal muscle strength of the knee extensors was determined quantitatively using a dynamometer. On both days, muscle strength was determined before a constant blood glucose level was obtained and after the blood glucose level had been kept constant at either 5 or 16 mmol/l for 3 h. Percentage of change from baseline at the two glycaemic levels were calculated and compared. In addition, the changes from baseline at these glycaemic levels were related to glucose turnover.

RESULTS

Following hyperglycaemia, a significant decrease in maximal isometric muscle strength was found as compared with normoglycaemia (86 vs. 104% of the initial level) (P = 0.018). In contrast, no alteration of maximal isokinetic muscle strength was found comparing normo- and hyperglycaemia (96 and 95%) (P = 0.74). Changes in muscle strength were not significantly related to either basal or hyperglycaemic glucose turnover.

CONCLUSIONS

A few hours of hyperglycaemia in Type 1 diabetic patients leads to a reduction of isometric muscle performance, whereas isokinetic muscle strength is unchanged. The reduction in muscle strength could play a role in the development of fatigue and is related more closely to ambient glucose concentrations than to systemic glucose availability.

Aerobic exercise capacity in normal adolescents and those with type 1 diabetes mellitus

OBJECTIVE

To compare the aerobic exercise capacity between normal adolescents and those with type 1 diabetes mellitus (T1DM).

METHODS

An experimental group with 72 individuals diagnosed with T1DM aged 9--20, time from diagnosis 4.9 +/- 3.6 yr, without clinical cardiopulmonary disease or anemia and a control group (C) with 46 healthy individuals aged 10--18, matched by age, weight, height, body mass index, and lean and fat mass (kg), underwent an incremental aerobic exercising test on a motorized treadmill, where gas exchange variables - peak pulmonary ventilation (VE), peak oxygen consumption (VO(2)), and carbon dioxide production (CO(2)) - as well as their heart rate (HR) and time to exhaustion were recorded.

RESULTS

Body mass composition had no significant difference between experimental and control groups, and male and female subjects had similar exercising performances. The mean of hemoglobin A1c in the control group was 5.2+/- 0.9% and in the diabetic group 8.1+/- 2.2%; p=0.000. The patients with T1DM showed lower levels of aerobic capacity than the control group. Their respective values for each variable were as follows: (i) maximal VO(2) (T1DM: 41.57+/-7.68 vs. C: 51.12+/- 9.94 mL/kg/min; p< 0.001) and (ii) maximal VE (T1DM: 76.39+/-19.93 vs. C: 96.90 +/- 25.72 mL/kg/min; p< 0.001). Patients with T1DM also had an earlier time to exhaustion (T1DM: 8.75+/-1.60 vs. 10.82+/-1.44 min).

CONCLUSIONS

Adolescent patients with T1DM showed a reduced aerobic exercising capacity when compared to healthy peers matched to anthropometric conditions. This potential condition should be taken into consideration by the time of evaluation of the aerobic performance of these patients with glycemic control level.

Determinants of exercise capacity in patients with type 2 diabetes

OBJECTIVE

Type 2 diabetes is associated with reduced exercise capacity, but the cause of this association is unclear. We sought the associations of impaired exercise capacity in type 2 diabetes.

RESEARCH DESIGN AND METHODS

Subclinical left ventricular (LV) dysfunction was sought from myocardial strain rate and the basal segmental diastolic velocity (Em) of each wall in 170 patients with type 2 diabetes (aged 56 +/- 10 years, 91 men), good quality echocardiographic images, and negative exercise echocardiograms. The same measurements were made in 56 control subjects (aged 53 +/- 10 years, 29 men). Exercise capacity was calculated in metabolic equivalents, and heart rate recovery (HRR) was measured as the heart rate difference between peak and 1 min after exercise. In subjects with type 2 diabetes, exercise capacity was correlated with clinical, therapeutic, biochemical, and echocardiographic variables, and significant independent associations were sought using a multiple linear regression model.

RESULTS

Exercise capacity, strain rate, Em, and HRR were significantly reduced in type 2 diabetes. Exercise capacity was associated with age (r = -0.37, P < 0.001), male sex (r = 0.26, P = 0.001), BMI (r = -0.19, P = 0.012), HbA(1c) (A1C; r = -0.22, P = 0.009), Em (r = 0.43, P < 0.001), HRR (r = 0.42, P < 0.001), diabetes duration (r = -0.18, P = 0.021), and hypertension history (r = -0.28, P < 0.001). Age (P < 0.001), male sex (P = 0.007), BMI (P = 0.001), Em (P = 0.032), HRR (P = 0.013), and A1C (P = 0.0007) were independent predictors of exercise capacity.

CONCLUSIONS

Reduced exercise capacity in patients with type 2 diabetes is associated with diabetes control, subclinical LV dysfunction, and impaired HRR.

Abnormal cardiac and skeletal muscle energy metabolism in patients with type 2 diabetes

BACKGROUND

It is well known that patients with type 2 diabetes have increased risk of cardiovascular disease, but it is not known whether they have underlying abnormalities in cardiac or skeletal muscle high-energy phosphate metabolism.

METHODS AND RESULTS

We studied 21 patients with type 2 diabetes with no evidence of coronary artery disease or impaired cardiac function, as determined by echocardiography, and 15 age-, sex-, and body mass index-matched control subjects. Cardiac high-energy phosphate metabolites were measured at rest using 31P nuclear magnetic resonance spectroscopy (MRS). Skeletal muscle high-energy phosphate metabolites, intracellular pH, and oxygenation were measured using 31P MRS and near infrared spectrophotometry, respectively, before, during, and after exercise. Although their cardiac morphology, mass, and function appeared to be normal, the patients with diabetes had significantly lower phosphocreatine (PCr)/ATP ratios, at 1.50+/-0.11, than the healthy volunteers, at 2.30+/-0.12. The cardiac PCr/ATP ratios correlated negatively with the fasting plasma free fatty acid concentrations. Although skeletal muscle energetics and pH were normal at rest, PCr loss and pH decrease were significantly faster during exercise in the patients with diabetes, who had lower exercise tolerance. After exercise, PCr recovery was slower in the patients with diabetes and correlated with tissue reoxygenation times. The exercise times correlated negatively with the deoxygenation rates and the hemoglobin (Hb)A1c levels and the reoxygenation times correlated positively with the HbA1c levels.

CONCLUSIONS

Type 2 diabetic patients with apparently normal cardiac function have impaired myocardial and skeletal muscle energy metabolism related to changes in circulating metabolic substrates.