Type 2 diabetic individuals have impaired leg blood flow responses to exercise: role of endothelium-dependent vasodilation

The effect of exercise on large artery haemodynamics in cystic fibrosis

BACKGROUND

Adult patients with cystic fibrosis (CF) have resting abnormal large artery haemodynamics. Here, we obtain further insight in patients with CF by evaluating haemodynamic response to physiological stress.

METHODS

Thirty-six stable CF patients mean (SD) age 28.9 (9.0)years and 25 controls matched for age, gender and body mass index were studied. Central haemodynamic parameters; including augmentation index (AIx) and wasted left ventricular pressure energy (∆E(W)) were determined pre, during and post light intensity cycle ergometry.

RESULTS

During exercise, despite a similar heart rate and blood pressure, patients had comparatively greater ∆E(W) (P=0.03) and trend towards greater AIx (P=0.07) than controls. Exercise ∆E(W) was greatest in patients with CF related diabetes (n=11). In all subjects, exercise ∆E(W) was related to age (r=0.54, P<0.001) and FEV(1)% predicted (r=-0.32, P=0.01).

CONCLUSIONS

Adults with CF have an abnormal haemodynamic response to exercise. This finding has deleterious implications for myocardial performance.

Effect of type 2 diabetes on the dynamic response characteristics of leg vascular conductance during exercise

In this study we tested the hypothesis that type 2 diabetes impairs the dynamic response of leg vascular conductance (LVC) during exercise. LVC (leg blood flow/mean arterial pressure) responses were studied during intermittent contractions of the calf muscle in subjects with type 2 diabetes (n = 9), heavy controls (n = 10) and lean controls (n = 8) using a biexponential function and an estimate of the mean response time (MRT). The time constant of the second phase of LVC was significantly greater in type 2 diabetes (66.4 ± 29.2 s) than the heavy (22.2 ± 13.4 s) and lean (21.8 ± 9.3 s) controls, resulting in a significantly greater MRT in the diabetic group (median [IQR] = 30.7 [24.6-46.5] s versus 16.3 [4.3-23.2] s and 18.4 [13.7-19.3] s). These data support the hypothesis and suggest that a slowed hyperaemic response in the exercising limb might contribute to exercise intolerance in diabetic subjects.

Glycemic status affects cardiopulmonary exercise response in athletes with type I diabetes

PURPOSE

This study aimed to (a) examine the influence of type I diabetes on the cardiopulmonary exercise response in trained subjects and (b) determine whether glycemic control affects these responses.

METHODS

The cardiopulmonary responses to maximal incremental cycle ergometry were compared in 12 Ironman triathletes with type I diabetes and 10 age- and sex-matched control subjects without diabetes. Athletes with type I diabetes were then stratified into low- (glycosylated hemoglobin (HbA1c) < 7%, n = 5) and high-HbA1c (HbA1c > 7%, n = 7) groups for comparison. Cardiac output, stroke volume, arterial blood pressure, and calculated systemic vascular resistance along with airway function were measured at rest and during steady-state exercise.

RESULTS

During peak exercise HR, stroke volume and cardiac output were not different between the groups with and without diabetes; however, forced expiratory flow at 50% of the forced vital capacity was lower in subjects with diabetes (P < 0.05). Within the group with diabetes, HbA1c was lower in the low-HbA1c versus high-HbA1c group (6.5 +/- 0.3 vs 7.8 +/- 0.4, respectively; P < 0.05), but training volume was not different. At rest, the low-HbA1c group had greater cardiac output and lower systemic vascular resistance than the high-HbA1c group, and all pulmonary function measurements were greater in the low-HbA1c group (P < 0.05). During peak exercise, the VO2, workload, HR, stroke volume, and cardiac output were greater in the low-HbA1c versus the high-HbA1c group (P < 0.05). In addition, all indices of pulmonary function were higher in the low-HbA1c group (P < 0.05). Finally, within the subjects with diabetes, there was a weak inverse correlation between HbA1c and exercise training volume (r2 = -0.352) and stroke volume (r2 = -0.339). These data suggest that highly trained individuals with type I diabetes can achieve the same cardiopulmonary exercise responses as trained subjects without diabetes, but these responses are reduced by poor glycemic control.

Effects of type II diabetes on exercising skeletal muscle blood flow in the rat

The purpose of the present investigation was to examine the muscle hyperemic response to steady-state submaximal running exercise in the Goto-Kakizaki (GK) Type II diabetic rat. Specifically, the hypothesis was tested that Type II diabetes would redistribute exercising blood flow toward less oxidative muscles and muscle portions of the hindlimb. GK diabetic (n = 10) and Wistar control (n = 8, blood glucose concentration, 13.7 ± 1.6 and 5.7 ± 0.2 mM, respectively, P < 0.05) rats were run at 20 m/min on a 10% grade. Blood flows to 28 hindlimb muscles and muscle portions as well as the abdominal organs and kidneys were measured in the steady state of exercise using radiolabeled 15-μm microspheres. Blood flow to the total hindlimb musculature did not differ between GK diabetic and control rats (161 ± 16 and 129 ± 15 ml·min(-1)·100 g(-1), respectively, P = 0.18). Moreover, there was no difference in blood flow between GK diabetic and control rats in 20 of the individual muscles or muscle parts examined. However, in the other eight muscles examined that typically are comprised of a majority of fast-twitch glycolytic (IIb/IIdx) fibers, blood flow was significantly greater (i.e., ↑31-119%, P < 0.05) in the GK diabetic rats. Despite previously documented impairments of several vasodilatory pathways in Type II diabetes these data provide the first demonstration that a reduction of exercising muscle blood flow during submaximal exercise is not an obligatory consequence of this condition in the GK diabetic rat.

Divergent effects of low-O(2) tension and iloprost on ATP release from erythrocytes of humans with type 2 diabetes: implications for O(2) supply to skeletal muscle

Erythrocytes release both O(2) and a vasodilator, ATP, when exposed to reduced O(2) tension. We investigated the hypothesis that ATP release is impaired in erythrocytes of humans with type 2 diabetes (DM2) and that this defect compromises the ability of these cells to stimulate dilation of resistance vessels. We also determined whether a general vasodilator, the prostacyclin analog iloprost (ILO), stimulates ATP release from healthy human (HH) and DM2 erythrocytes. Finally, we used a computational model to compare the effect on tissue O(2) levels of increases in blood flow directed to areas of increased O(2) demand (erythrocyte ATP release) with nondirected increases in flow (ILO). HH erythrocytes, but not DM2 cells, released increased amounts of ATP when exposed to reduced O(2) tension (Po(2) < 30 mmHg). In addition, isolated hamster skeletal muscle arterioles dilated in response to similar decreases in extraluminal O(2) when perfused with HH erythrocytes, but not when perfused with DM2 erythrocytes. In contrast, both HH and DM2 erythrocytes released ATP in response to ILO. In the case of DM2 erythrocytes, amounts of ATP released correlated inversely with glycemic control. Modeling revealed that a functional regulatory system that directs blood flow to areas of need (low O(2)-induced ATP release) provides appropriate levels of tissue oxygenation and that this level of the matching of O(2) delivery with demand in skeletal muscle cannot be achieved with a general vasodilator. These results suggest that the inability of erythrocytes to release ATP in response to exposure to low-O(2) tension could contribute to the peripheral vascular disease of DM2.

Attenuated purinergic receptor function in patients with type 2 diabetes

OBJECTIVE

Extracellular nucleotides and nucleosides are involved in regulation of skeletal muscle blood flow. Diabetes induces cardiovascular dysregulation, but the extent to which the vasodilatatory capacity of nucleotides and nucleosides is affected in type 2 diabetes is unknown. The present study investigated 1) the vasodilatatory effect of ATP, uridine-triphosphate (UTP), and adenosine (ADO) and 2) the expression and distribution of P2Y(2) and P2X(1) receptors in skeletal muscles of diabetic subjects.

RESEARCH DESIGN AND METHODS

In 10 diabetic patients and 10 age-matched control subjects, leg blood flow (LBF) was measured during intrafemoral artery infusion of ATP, UTP, and ADO, eliciting a blood flow equal to knee-extensor exercise at 12 W (approximately 2.6 l/min).

RESULTS

The vasodilatatory effect of the purinergic system was 50% lower in the diabetic group as exemplified by an LBF increase of 274 +/- 37 vs. 143 +/- 26 ml/micromol ATP x kg, 494 +/- 80 vs. 234 +/- 39 ml/micromol UTP x kg, and 14.9 +/- 2.7 vs. 7.5 +/- 0.6 ml/micromol ADO x kg in control and diabetic subjects, respectively, thus making the vasodilator potency as follows: UTP control subjects (100) > ATP control subjects (55) > UTP diabetic subjects (47) > ATP diabetic subjects (29) > ADO control subjects (3) > ADO diabetic subjects (1.5). The distribution and mRNA expression of receptors were similar in the two groups.

CONCLUSIONS

The vasodilatatory effect of the purinergic system is severely reduced in type 2 diabetic patients. The potency of nucleotides varies with the following rank order: UTP > ATP > ADO. This is not due to alterations in receptor distribution and mRNA expression, but may be due to differences in receptor sensitivity.

Muscle blood flow responses to dynamic exercise in young obese humans

Exercise is a common nonpharmacological way to combat obesity; however, no studies have systematically tested whether obese humans exhibit reduced skeletal muscle blood flow during dynamic exercise. We hypothesized that exercise-induced blood flow to skeletal muscle would be lower in young healthy obese subjects (body mass index of >30 kg/m(2)) compared with lean subjects (body mass index of <25 kg/m(2)). We measured blood flow (Doppler Ultrasound of the brachial and femoral arteries), blood pressure (auscultation, Finapress), and heart rate (ECG) during rest and two forms of single-limb, steady-state dynamic exercise: forearm exercise (20 contractions/min at 4, 8, and 12 kg) and leg exercise (40 kicks/min at 7 and 14 W). Forearm exercise increased forearm blood flow (FBF) similarly in both groups (P > 0.05; obese subjects n = 9, lean subjects n = 9). When FBF was normalized for perfusion pressure, forearm vascular conductance was not different between groups at increasing workloads (P > 0.05). Leg exercise increased leg blood flow (LBF) similarly in both groups (P > 0.05; obese subjects n = 10, lean subjects n = 12). When LBF was normalized for perfusion pressure, leg vascular conductance was not different between groups at increasing workloads (P > 0.05). These results were confirmed when relative blood flow was expressed at average relative workloads. In conclusion, our results show that obese subjects exhibited preserved FBF and LBF during dynamic exercise.

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.

Abnormal vascular reactivity at rest and exercise in obese boys

BACKGROUND

Obese children exhibit vascular disorders at rest depending on their pubertal status, degree of obesity, and level of insulin resistance. However, data regarding their vascular function during exercise remain scarce. The aims of the present study were to evaluate vascular morphology and function at rest, and lower limb blood flow during exercise, in prepubertal boys with mild-to-moderate obesity and in lean controls.

MATERIALS AND METHODS

Twelve moderately obese prepubertal boys [Body Mass Index (BMI: 23.9+/-2.6 kg m(-2))] and thirteen controls (BMI:17.4+/-1.8 kg m(-2)), matched for age (mean age: 11.6+/-0.6 years) were recruited. We measured carotid intima-media thickness (IMT) and wall compliance and incremental elastic modulus, resting brachial flow-mediated dilation (FMD) and nitrate-dependent dilation (NDD), lower limb blood flow during local knee-extensor incremental and maximal exercise, body fat content (DEXA), blood pressure, blood lipids, insulin and glucose.

RESULTS

Compared to lean controls, obese boys had greater IMT (0.47+/-0.06 vs. 0.42+/-0.03 mm, P<0.05) but lower FMD (4.6+/-2.8 vs. 8.8+/-3.2%, P<0.01) in spite of similar maximal shear rate, without NDD differences. Lower limb blood flow (mL min(-1).100 g(-1)) increased significantly from rest to maximal exercise in both groups, although obese children reached lower values than lean counterparts whatever the exercise intensity.

CONCLUSIONS

Mild-to-moderate obesity in prepubertal boys without insulin resistance is associated with impaired endothelial function and blunted muscle perfusion response to local dynamic exercise without alteration of vascular smooth muscle reactivity.

Reduced leg blood flow during submaximal exercise in type 2 diabetes

It is unclear whether impaired cardiac and/or vascular function contribute to exercise intolerance in patients with type 2 diabetes.

PURPOSE

Magnetic resonance imaging (MRI) was used to determine whether reductions in cardiac output and/or femoral arterial blood flow contribute to reduced aerobic capacity in patients with type 2 diabetes.

METHODS

Cardiac and femoral arterial blood flow MRI scans were performed at rest and during low-intensity leg exercise in eight patients with type 2 diabetes and 11 healthy individuals. Maximal aerobic capacity VO(2 max) and maximal oxygen pulse were also determined in all participants.

RESULTS

V O(2 max) was 20% lower and maximal oxygen pulse was 16% lower in patients with type 2 diabetes (P < 0.05), whereas maximal heart rate was the same between groups. Low-intensity exercise induced a 20% increase in heart rate and cardiac output as well as a 60-70% increase in femoral blood flow in both groups (P < 0.05). Femoral arterial blood flow indexed to thigh lean mass was reduced during exercise in patients with type 2 diabetes compared with healthy individuals. Stroke volume indexed to fat-free mass was lower in patients with type 2 diabetes, but greater heart rate allowed cardiac output to be maintained during submaximal exercise.

CONCLUSIONS

These findings suggest that impaired femoral arterial blood flow, an indirect marker of muscle perfusion, affects low-intensity exercise performance in patients with type 2 diabetes. However, because of lower exercising stroke volume, we propose that femoral arterial blood flow and, possibly, cardiac output, limit V O(2 max) in patients with type 2 diabetes.

Patients with type 2 diabetes have exaggerated brachial and central exercise blood pressure: relation to left ventricular relative wall thickness

BACKGROUND

A hypertensive response to exercise has prognostic significance. Patients with type 2 diabetes have vascular abnormalities which may predispose to exaggerated brachial and central blood pressure (BP) during exercise. This study aimed to test this hypothesis and to determine the clinical significance of high exercise BP by examining its relation to left ventricular (LV) mass.

METHODS

Brachial and central BP were recorded at rest and in response to maximal exercise in 73 diabetic patients (aged 54 +/- 10 years) and 73 controls (aged 53 +/- 12 years). Brachial BP was recorded using mercury sphygmomanometry and LV mass using 2D-echocardiography. Central BP was estimated by radial tonometry using an exercise-validated generalized transfer function.

RESULTS

At rest there were no significant (P > 0.05) differences between groups in brachial or central BP. The diabetic patients had significantly increased exercise brachial systolic BP (SBP: 199 +/- 25 mm Hg vs. 185 +/- 21 mm Hg; P = 0.002) and central SBP (158 +/- 17 mm Hg vs. 149 +/- 15 mm Hg; P = 0.002). There was a significantly higher prevalence of an exaggerated exercise BP response (> or =210/105 mm Hg; men and > or =190/105 mm Hg; women) in the diabetic patients (51% vs. 22%; P < 0.01). Compared with those with normal exercise BP, LV relative wall thickness (RWT) was significantly higher (0.41 +/- 0.09 vs. 0.36 +/- 0.08; P < 0.05) and LV hypertrophy was more prevalent (35% vs. 16%; P < 0.05) in those with a hypertensive response. After accounting for other confounding variables, exercise central SBP remained independently associated with LV RWT (beta = 0.22; P = 0.006).

CONCLUSION

Diabetic patients are more likely to exhibit exaggerated exercise BP. Regardless of disease status, high exercise central SBP may contribute to cardiovascular risk via adverse cardiac remodeling.

Skeletal muscle deoxygenation after the onset of moderate exercise suggests slowed microvascular blood flow kinetics in type 2 diabetes

OBJECTIVE

People with type 2 diabetes have impaired exercise responses even in the absence of cardiovascular complications. One key factor associated with the exercise intolerance is abnormally slowed oxygen uptake (VO2) kinetics during submaximal exercise. The mechanisms of this delayed adaptation during exercise are unclear but probably relate to impairments in skeletal muscle blood flow. This study was conducted to compare skeletal muscle deoxygenation (deoxygenated hemoglobin/myoglobin [HHb]) responses and estimated microvascular blood flow (Qm) kinetics in type 2 diabetic and healthy subjects after the onset of moderate exercise.

RESEARCH DESIGN AND METHODS

Pulmonary VO2 kinetics and [HHb] (using near-infrared spectroscopy) were measured in 11 type 2 diabetic and 11 healthy subjects during exercise transitions from unloaded to moderate cycling exercise. Qm responses were calculated using VO2 kinetics and [HHb] responses via rearrangement of the Fick principle.

RESULTS

VO2 kinetics were slowed in type 2 diabetic compared with control subjects (43.8 +/- 9.6 vs. 34.2 +/- 8.2 s, P < 0.05), and the initial [HHb] response after the onset of exercise exceeded the steady-state level of oxygen extraction in type 2 diabetic compared with control subjects. The mean response time of the estimated Qm increase was prolonged in type 2 diabetic compared with healthy subjects (47.7 +/- 14.3 vs. 35.8 +/- 10.7 s, P < 0.05).

CONCLUSIONS

Type 2 diabetic skeletal muscle demonstrates a transient imbalance of muscle O2 delivery relative to O2 uptake after onset of exercise, suggesting a slowed Qm increase in type 2 diabetic muscle. Impaired vasodilatation due to vascular dysfunction in type 2 diabetes during exercise may contribute to this observation. Further study of the mechanisms leading to impaired muscle oxygen delivery may help explain the abnormal exercise responses in type 2 diabetes.

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.

The influence of obesity on calf blood flow and vascular reactivity in older adults

OBJECTIVE

To determine whether differences in vascular reactivity existed among normal weight, overweight, and obese older men and women, and to examine the association between abdominal fat distribution and vascular reactivity.

METHODS

Eighty-seven individuals who were 60 years of age or older (age = 69 +/- 7 yrs; mean +/- SD) were grouped into normal weight (BMI < 25; n = 30), overweight (BMI > or = 25 and < 30; n = 28), or obese (BMI > or = 30; n = 29) categories. Calf blood flow (BF) was assessed by venous occlusion strain-gauge plethysmography at rest and post-occlusive reactive hyperemia.

RESULTS

Post-occlusive reactive hyperemia BF was lower (p = 0.038) in the obese group (5.55 +/- 4.67%/min) than in the normal weight group (8.34 +/- 3.89%/min). Additionally, change in BF from rest to post-occlusion in the obese group (1.93 +/- 2.58%/min) was lower (p = 0.001) than in the normal weight group (5.21 +/- 3.59%/min), as well as the percentage change (75 +/- 98% vs. 202 +/- 190%, p = 0.006, respectively). After adjusting for age, prevalence in hypertension and calf skinfold thickness, change in BF values remained lower (p < 0.05) in obese subjects compared to the normal weight subjects. Lastly, the absolute and percentage change in BF were significantly related to BMI (r = -0.44, p < 0.001, and r = -0.37, p < 0.001, respectively) and to waist circumference (r = -0.36, p = 0.001, and r = -0.32, p = 0.002).

CONCLUSION

Obesity and abdominal adiposity impair vascular reactivity in older men and women, and these deleterious effects on vascular reactivity are independent of conventional risk factors.

Responses to acute exercise in type 2 diabetes, with an emphasis on metabolism and interaction with oral hypoglycemic agents and food intake

In people with type 1 diabetes mellitis (DM), insulin administration, food intake, and exercise have to be carefully matched to avoid either hypo- or hyperglycemia. People with type 2 DM have some insulin secretion, which changes with needs. Accordingly, during exercise, these people do not run the same metabolic risks as people with type 1 DM. However, a contraction-mediated increase in glucose clearance in muscle is intact in type 2 DM. Therefore, , in the postabsorptive state in diet-treated type 2 DM, a marked reduction in hyperglycemia can occur during prolonged moderate exercise. Sulfonylurea drugs augment the rate of decline in plasma glucose, because stimulation of insulin secretion reduces hepatic glucose production. After abstention from sulfonylurea for 5 days, the rate of decrease in plasma glucose with exercise is also enhanced, but from a higher glucose level. In the postabsorptive state, brief vigourous exercise elicits an increase in plasma glucose concentration, reflecting an exaggerated counterregulatory hormone response and glucose production. Moreover, insulin sensitivity is reduced in the early postexercise period. In the postprandial state, both prolonged moderate exercise and intermittent high-intensity exercise markedly decrease meal-induced increases in glucose, insulin, and C-peptide concentrations, whereas glucose appearance in plasma is unchanged. When exercise bouts are isocaloric, responses are identical, indicating that overall energy expenditure, and not peak exercise intensity, is the major determinant of exercise-induced changes in overall glucose homeostasis and insulin secretion in type 2 DM. Neither prolonged moderate nor intermittent high-intensity exercise performed in the postprandial state influences glucose or insulin responses to a subsequent meal. Finally, in people with type 2 DM, after a high-fat meal, prolonged moderate exercise reduces the exaggerated increases in plasma concentrations of triglycerides contained in chylomicrons and very low-density lipoproteins.

31P MR spectroscopy and in vitro markers of oxidative capacity in type 2 diabetes patients

BACKGROUND

Skeletal muscle mitochondrial function in type 2 diabetes (T2D) is currently being studied intensively. In vivo (31)P magnetic resonance spectroscopy ((31)P MRS) is a noninvasive tool used to measure mitochondrial respiratory function (MIFU) in skeletal muscle tissue. However, microvascular co-morbidity in long-standing T2D can interfere with the (31)P MRS methodology.

AIM

To compare (31)P MRS-derived parameters describing in vivo MIFU with an in vitro assessment of muscle respiratory capacity and muscle fiber-type composition in T2D patients.

METHODS

(31)P MRS was applied in long-standing, insulin-treated T2D patients. (31)P MRS markers of MIFU were measured in the M. vastus lateralis. Muscle biopsy samples were collected from the same muscle and analyzed for succinate dehydrogenase activity (SDH) and fiber-type distribution.

RESULTS

Several (31)P MRS parameters of MIFU showed moderate to good correlations with the percentage of type I fibers and type I fiber-specific SDH activity (Pearson's R between 0.70 and 0.75). In vivo and in vitro parameters of local mitochondrial respiration also correlated well with whole-body fitness levels (VO (2peak)) in these patients (Pearson's R between 0.62 and 0.90).

CONCLUSION

Good correlations exist between in vivo and in vitro measurements of MIFU in long-standing insulin-treated T2D subjects, which are qualitatively and quantitatively consistent with previous results measured in healthy subjects. This justifies the use of (31)P MRS to measure MIFU in relation to T2D.

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.

Effects of Type II diabetes on capillary hemodynamics in skeletal muscle

Microcirculatory red blood cell (RBC) hemodynamics are impaired within skeletal muscle of Type I diabetic rats (Kindig CA, Sexton WL, Fedde MR, and Poole DC. Respir Physiol 111: 163–175, 1998). Whether muscle microcirculatory dysfunction occurs in Type II diabetes, the more prevalent form of the disease, is unknown. We hypothesized that Type II diabetes would reduce the proportion of capillaries supporting continuous RBC flow and RBC hemodynamics within the spinotrapezius muscle of the Goto-Kakizaki Type II diabetic rat (GK). With the use of intravital microscopy, muscle capillary diameter ( dc), capillary lineal density, capillary tube hematocrit (Hctcap), RBC flux ( FRBC), and velocity ( VRBC) were measured in healthy male Wistar (control: n = 5, blood glucose, 105 ± 5 mg/dl) and male GK ( n = 7, blood glucose, 263 ± 34 mg/dl) rats under resting conditions. Mean arterial pressure did not differ between groups ( P > 0.05). Sarcomere length was set to a physiological length (∼2.7 μm) to ensure that muscle stretching did not alter capillary hemodynamics; dc was not different between control and GK rats ( P > 0.05), but the percentage of RBC-perfused capillaries (control: 93 ± 3; GK: 66 ± 5 %), Hctcap, VRBC, FRBC, and O2 delivery per unit of muscle were all decreased in GK rats ( P < 0.05). This study indicates that Type II diabetes reduces both convective O2 delivery and diffusive O2 transport properties within muscle microcirculation. If these microcirculatory deficits are present during exercise, it may provide a basis for the reduced O2 exchange characteristic of Type II diabetic patients.

Effects of Type II diabetes on muscle microvascular oxygen pressures

We tested the hypothesis that muscle microvascular O2 pressure (PmvO2; reflecting the O2 delivery (QO2) to O2 uptake (VO2) ratio) would be lowered in the spinotrapezius muscle of Goto-Kakizaki (GK) Type II diabetic rats (n=7) at rest and during twitch contractions when compared to control (CON; n=5) rats. At rest, PmvO2 was lower in GK versus CON rats (CON: 29+/-2; GK: 18+/-2Torr; P<0.05). At the onset of contractions, GK rats evidenced a faster change in PmvO2 than CON (i.e., time constant (tau); CON: 16+/-4; GK: 6+/-2s; P<0.05). In contrast to the monoexponential fall in PmvO2 to the steady-state level seen in CON, GK rats exhibited a biphasic PmvO2 response that included a blunted (or non-existent) PmvO2 decrease followed by recovery to a steady-state PmvO2 that was at, or slightly above, resting values. Compared with CON, this decreased PmvO2 across the transition to a higher metabolic rate in Type II diabetes would be expected to impair blood-muscle O2 exchange and contractile function.

Impaired exercise-induced blood volume in type 2 diabetes with or without peripheral arterial disease measured by continuous-wave near-infrared spectroscopy

OBJECTIVE

Diabetes is a significant risk factor for peripheral arterial disease (PAD) and is associated with accelerated atherosclerosis and limb loss. However, the pathophysiology involved in PAD is unclear. This study was conducted to evaluate the hemodynamic response to exercise of patients with and without diabetes and PAD.

RESEARCH DESIGN AND METHODS

The hemodynamic response in calf muscles of patients with diabetes, PAD, or both was determined using near-infrared spectroscopy (NIRS). Patients performed both a plantar-flexion and treadmill-walking exercise regimen.

RESULTS

Skeletal muscle capillary blood volume expansion during exercise, as measured by NIRS, was significantly impaired in the lower extremities of diabetic patients with a normal ankle-brachial index. The relative deoxygenation and oxygenation recovery times measured by NIRS correlates significantly with the presence of PAD.

CONCLUSIONS

Patients with diabetes have reduced capillary volume expansion even without PAD. This is likely due to impaired vasodilation secondary to endothelial dysfunction. Further studies are needed to determine whether pharmaceutical intervention improves the blood volume expansion in the diabetic state.

Supplementation with omega-3 polyunsaturated fatty acids augments brachial artery dilation and blood flow during forearm contraction

Omega-3 polyunsaturated fatty acids such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) have beneficial effects on the heart and vasculature. We tested the hypothesis that 6 weeks of dietary supplementation with DHA (2.0 g/day) and EPA (3.0 g/day) enhances exercise-induced increases in brachial artery diameter and blood flow during rhythmic exercise. In seven healthy subjects, blood pressure, heart rate and brachial artery diameter, blood flow, and conductance were assessed before and during the last 30 s of 90 s of rhythmic handgrip exercise (30% of maximal handgrip tension). Blood pressure (MAP), heart rate (HR), and brachial artery vascular conductance were also determined. This paradigm was also performed in six other healthy subjects who received 6 weeks of placebo (safflower oil). Placebo treatment had no effect on any variable. DHA and EPA supplementation enhanced contraction-induced increases in brachial artery diameter (0.28+/-0.04 vs. 0.14+/-0.03 mm), blood flow (367+/-65 vs. 293+/-55 ml min-1) and conductance (3.86+/-0.71 vs. 2.89+/-0.61 ml min-1 mmHg-1) (P<0.05). MAP and HR were unchanged. Results indicate that treatment with DHA and EPA enhances brachial artery blood flow and conductance during exercise. These findings may have implications for individuals with cardiovascular disease and exercise intolerance (e.g., heart failure).

Effect of an 8-week resistance training program on cutaneous perfusion in type 2 diabetes

A positive association has previously been demonstrated between chronic aerobic exercise and prior maximal exercise and enhanced dorsal foot skin perfusion in physically active individuals with type 2 diabetes. The current study examined whether an 8-week resistance training program would also positively affect cutaneous perfusion in type 2 diabetic individuals. Ten individuals with type 2 diabetes and nine similar nondiabetic controls participated in 8 weeks of moderate-intensity resistance training. Prior to training, dorsal foot cutaneous perfusion was measured noninvasively by continuous laser Doppler assessment at baseline and during localized heating to 44 degrees C. These measurements were repeated exactly 48-72 h following 8 weeks of resistance training performed 3 days per week. Interstitial nitric oxide (NO) levels were measured concurrently in the contralateral foot dorsum. Neither subject group experienced significant increases in dorsal foot perfusion responsiveness during local heating to 44 degrees C following moderate resistance training, nor did the training significantly enhance baseline skin perfusion. Interstitial NO levels were not significantly different under any condition. At baseline, groups differed only on fasting serum glucose and overall glycemic control. In conclusion, the responsiveness of cutaneous perfusion in response to heating to 44 degrees C is not significantly enhanced by 8 weeks of moderate resistance training in diabetic individuals or their matched controls, independent of interstitial NO levels.

Altered arachidonic acid metabolism impairs functional vasodilation in metabolic syndrome

These studies tested the hypothesis that in obese Zucker rats (OZRs), a model of metabolic syndrome, the impaired functional vasodilation is due to increased thromboxane receptor (TP)-mediated vasoconstriction and/or decreased prostacyclin-induced vasodilation. Spinotrapezius arcade arterioles from 12-wk-old lean (LZR) and OZR were chosen for microcirculatory observation. Arteriolar diameter (5 LZR and 6 OZR) was measured after 2 min of muscle stimulation in the absence or presence of 1 microM SQ-29548 (TP antagonist). Additionally, arteriolar diameter (6 for each group) was measured after application of iloprost (prostacyclin analog; 0.28, 2.8, and 28 microM), arachidonic acid (10 microM), and sodium nitroprusside (0.1, 1, and 10 microM) in the absence or presence of 1 microM SQ-29548. A 10 microM concentration of adenosine was used to induce a maximal dilation. Basal diameters were not different between LZRs and OZRs. Functional hyperemia and arachidonic acid-mediated vasodilations were significantly attenuated in OZR compared with LZR, and treatment with 1 microM SQ-29548 significantly enhanced the dilations in OZRs, although it had no effect in LZRs. Vasodilatory responses to iloprost and sodium nitroprusside (1 and 10 microM) were significantly reduced in OZR. Adenosine-mediated vasodilation was not different between groups. These results suggest that the impaired functional dilation in the OZR is due to an increased TP-mediated vasoconstriction and a decreased PGI2-induced vasodilation.

Role of exercise training on cardiovascular disease in persons who have type 2 diabetes and hypertension

Exercise training is an essential component in the medical management of patients who have type 2 diabetes and hypertension. Regular exercise improves the cardiovascular health of individuals who have these conditions through multiple mechanisms (Fig. 1). These mechanisms include improvements in endothelial vasodilator function,left ventricular diastolic function, arterial stiffness.systematic inflammation, and reducing left ventricular mass. Exercise training also reduces total and abdominal fat, which mediate improvements in insulin sensitivity and blood pressure, and possibly, endothelial function. Persons who are in a prediabetic stage or those who have the metabolic syndrome may be able to prevent or delay the progression to overt diabetes by adopting a healthier lifestyle, of which increasing habitual levels of physical activity isa vital component. Most persons who have diabetes and hypertension or are at risk for these conditions should be able to initiate an exercise program safely after appropriate medical screen-ing and the establishment of an individualized exercise prescription. Despite the increasing amount of evidence that shows the benefits of exercise training, this modality of prevention and treatment continues to be underused. Although patients' lack of knowledge of the benefits of exercise or lack of motivation contributes to this underuse, a lack of clear and specific guidelines from health care professionals also is an important factor. Clinicians need to educate patients about the benefits of exercise for managing their type 2 diabetes and assist in formulating specific advice for increasing physical activity. Specific instructions should be given to patients, rather than general advice, such as "you should exercise more often." Many cardiac re-habilitation and clinical exercise programs can accommodate patients who have type 2 diabetes and hypertension. Such programs can establish individualized exercise prescriptions and provide an environment that is conducive for "lifestyle change" that underlies long-term compliance to exercise and risk factor modification.

Different vasodilator responses of human arms and legs

Forearm vascular responses to intra-arterial infusions of endothelium-dependent and -independent vasodilators have been thoroughly characterized in humans. While the forearm is a well-established experimental model for studying human vascular function, it is of limited consequence to systemic cardiovascular control owing to its small muscle mass and blood flow requirements. In the present study we determined whether these responses could be generalized to the leg. Based upon blood pressure differences between the leg and arm during upright posture, we hypothesized that the responsiveness to endothelium-dependent vasodilators would be greater in the forearm than the leg. Brachial and femoral artery blood flow (Q, ultrasound Doppler) at rest and during intra-arterial infusions of endothelium-dependent (acetylcholine and substance P) and -independent (sodium nitroprusside) vasodilators were measured in eight healthy men (22-27 years old). Resting blood flows in the forearm before infusion of acetylcholine, substance P or sodium nitroprusside were 25 +/- 4, 30 +/- 7 and 29 +/- 5 ml min(-1), respectively, and in the leg were 370 +/- 32, 409 +/- 62 and 330 +/- 30 ml min(-1), respectively. At the highest infusion rate of acetylcholine (16 microg (100 ml tissue)(-1) min(-1)) there was a greater (P < 0.05) increase in Q to the forearm (1864 +/- 476%) than to the leg (569 +/- 86%). Similarly, at the highest infusion rate of substance P (125 pg (100 ml tissue)(-1) min(-1)) there was a greater (P < 0.05) increase in Q to the forearm (911 +/- 286%) than to the leg (243 +/- 58%). The responses to sodium nitroprusside (1 microg (100 ml tissue)(-1) min(-1)) were also greater (P < 0.05) in the forearm (925 +/- 164%) than in the leg (326 +/- 65%). These data indicate that vascular responses to both endothelium-dependent and -independent vasodilator agents are blunted in the leg compared to the forearm.

The Role of Exercise in the Treatment of Cardiovascular Disease Associated with Type 2 Diabetes Mellitus

The role of exercise training in the prevention and treatment of type 2 diabetes mellitus has been studied extensively over the past two decades. Although the primary treatment aim for patients with type 2 diabetes is metabolic control, the morbidity and mortality associated with the disease is more a function of cardiovascular disease. As exercise is associated with favourable reductions in the risk for cardiovascular disease in other high-risk populations, here we explore the role of exercise in the treatment of cardiovascular maladaptations associated with type 2 diabetes. The cardiovascular adaptation to type 2 diabetes is characterised by hypertrophy, stiffening and loss of functional reserve. Clinically, the cardiovascular adaptations to the diabetic state are associated with an increased risk for cardiovascular disease. Functionally, these adaptations have been shown to contribute to a reduced exercise capacity, which may explain the reduced cardiovascular fitness observed in this population. Exercise training is associated with improved exercise capacity in various populations, including type 2 diabetes. Several structural and functional adaptations within the cardiovascular system following exercise training could explain these findings, such as reductions in ventricular and vascular structural hypertrophy and compliance coupled with increased functional reserve. Although these cardiovascular adaptations to aerobic exercise training have been well documented in older populations with similar decrements in cardiovascular fitness and function, they have yet to be examined in patients with type 2 diabetes. For this reason, we contend that exercise training may be an excellent therapeutic adjunct in the treatment of diabetic cardiovascular disease.