Abnormal oxygen uptake kinetic responses in women with type II diabetes mellitus

V̇o2 on-kinetics in isolated canine muscle in situ during slowed convective O2 delivery

The purpose of this study was to examine O2 uptake (V̇o2) on-kinetics when the spontaneous blood flow (and therefore O2 delivery) on-response was slowed by 25 and 50 s. The isolated gastrocnemius muscle complex (GS) in situ was studied in six anesthetized dogs during transitions from rest to a submaximal metabolic rate (≈50–70% of peak V̇o2). Four trials were performed: 1) a pretrial in which resting and steady-state blood flows were established, 2) a control trial in which the blood flow on-kinetics mean response time (MRT) was set at 20 s (CT20), 3) an experimental trial in which the blood flow on-kinetics MRT was set at 45 s (EX45), and 4) an experimental trial in which the blood flow on-kinetics MRT was set at 70 s (EX70). Slowing O2 delivery via slowing blood flow on-kinetics resulted in a linear slowing of the V̇o2 on-kinetics response ( R = 0.96). Average MRT values for CT20, EX45, and EX70 V̇o2 on-kinetics were (means ± SD) 17 ± 2, 23 ± 4, and 26 ± 3 s, respectively ( P < 0.05 among all). During these transitions, slowing blood flow resulted in greater muscle deoxygenation (as indicated by near-infrared spectroscopy), suggesting that lower intracellular Po2 values were reached. In this oxidative muscle, V̇o2 and O2 delivery were closely matched during the transition period from rest to steady-state contractions. In conjunction with our previous work showing that speeding O2 delivery did not alter V̇o2 on-kinetics under similar conditions, it appears that spontaneously perfused skeletal muscle operates at the nexus of sufficient and insufficient O2 delivery in the transition from rest to contractions.

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.

Cardiac output is not related to the slowed O2 uptake kinetics in type 2 diabetes

PURPOSE

This study aimed to investigate whether cardiac output (CO) responses were related to VO2 kinetics during cycling in type 2 diabetes.

METHODS

A total of 9 middle-aged women with uncomplicated type 2 diabetes, 9 nondiabetic overweight women, and 11 nondiabetic lean women were recruited. Initially, the ventilatory threshold (VT) and peak VO2 were determined during a maximal graded test. Then, on two separate days, subjects completed three 7-min bouts of constant-load cycling at each of three intensities: 50% VT, 80% VT, and midpoint between VT and peak VO2 (50% Δ). CO (inert gas rebreathing) was recorded at 30 and 240 s of an additional bout at each intensity. VO2 kinetic parameters were determined by fitting a biexponential (50% VT and 80% VT) or triexponential (50% Δ) function to the VO2 data.

RESULTS

Peak VO2 was significantly lower in type 2 diabetes compared with the two nondiabetic groups (P < 0.05). The time constant of phase 2 was significantly greater (P < 0.05) in type 2 diabetes compared with the nondiabetic heavy and lean groups at 50% VT (34.2 ± 15.7 vs 15.4 ± 7.3 and 20.2 ± 9.7 s) and 80% VT (39.1 ± 9.0 vs 24.8 ± 8.8 and 36.8 ± 7.9 s), but none of the VO2 kinetic parameters were different at 50% Δ. CO responses during exercise were not different among the three groups, and at 80% VT, the change in CO from 30 to 240 s was significantly larger in type 2 diabetes compared with the two nondiabetic groups.

CONCLUSIONS

The results confirm that type 2 diabetes slows the dynamic response of VO2 during light and moderate relative intensity exercise in females but that this occurs in the absence of any slowing of the CO response during the initial period of exercise.

Exercise attenuates the premature cardiovascular aging effects of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2D) is an example of a disease process that results in decrements in function additional to those imposed by the inexorable 'primary aging' process. These decrements due to disease, rather than primary aging, can be termed 'secondary aging', and include the premature development (as early as adolescence) of asymptomatic preclinical cardiovascular abnormalities (e.g. endothelial dysfunction, arterial stiffness, diastolic dysfunction), as well as impaired exercise performance. These abnormalities are important, as they are associated with greater cardiovascular morbidity and mortality in people with and without T2D. A better understanding of the pathophysiology of secondary cardiovascular aging in people with T2D is warranted, and an evaluation of the benefits of existing treatments for these abnormalities is useful (e.g. exercise training). The focus of this review is to discuss the data relevant to the following key postulates: (a) T2D causes premature cardiovascular aging; (b) in contrast to primary cardiovascular aging, the premature cardiovascular aging of T2D may be modifiable with exercise. The exercise-focused perspective for this review is appropriate because impairments in exercise performance are markers of premature cardiovascular aging in T2D, and also because exercise training shows promise to attenuate some aspects of cardiovascular aging during the preclinical stage.

Oxygen uptake before and after the onset of claudication during a 6-minute walk test

OBJECTIVE

This study compared oxygen uptake before and after the onset of claudication in individuals with peripheral artery disease (PAD) during a 6-minute walk test, and identified predictors of the change in oxygen uptake after the onset of claudication pain.

METHODS

The study included 50 individuals with PAD. During a 6-minute walk test, 33 experienced claudication (pain group), and 17 were pain-free (pain-free group). Oxygen uptake and ambulatory cadence were the primary outcomes evaluated during the 6-minute walk test.

RESULTS

The pain group experienced onset of claudication pain at a mean (standard deviation) of 179 (45) meters and continued to walk to achieve a 6-minute walk distance of 393 (74) meters, which was similar to the 401 (76) meters walked in the pain-free group (P = .74). Oxygen uptake increased (P < .0001) after the onset of pain in the pain group, and this change was greater (P = .025) than the increase in oxygen uptake from the second to fifth minutes of walking in the pain-free group. Ambulatory cadence decreased after the onset of pain in the pain group (P = .0003). The change in oxygen uptake was associated with metabolic syndrome (P = .0023), 6-minute walk distance (P = .0037), age (P = .0041), and oxygen uptake during the second minute of the test (P = .012).

CONCLUSION

Claudication increases oxygen uptake of self-paced, over-the-ground ambulation, despite a decrease in cadence. The pain-mediated increase in oxygen uptake was blunted in individuals with metabolic syndrome, suggesting that the ability to increase oxygen uptake during ambulation is impaired. The clinical significance is that claudication increases the metabolic cost of ambulation, thereby increasing the relative intensity of exercise and reducing the tolerance to sustain ambulation.

Dynamics of muscle microcirculatory and blood-myocyte O(2) flux during contractions

The O(2) requirements of contracting skeletal muscle may increase 100-fold above rest. In 1919, August Krogh's brilliant insights recognized the capillary as the principal site for this increased blood-myocyte O(2) flux. Based on the premise that most capillaries did not sustain RBC flux at rest, Krogh proposed that capillary recruitment [i.e. initiation of red blood cell (RBC) flux in previously non-flowing capillaries] increased the capillary surface area available for O(2) flux and reduced mean capillary-to-mitochondrial diffusion distances. More modern experimental approaches reveal that most muscle capillaries may support RBC flux at rest. Thus, rather than contraction-induced capillary recruitment per se, increased RBC flux and haematocrit within already-flowing capillaries probably elevate perfusive and diffusive O(2) conductances and hence blood-myocyte O(2) flux. Additional surface area for O(2) exchange is recruited but, crucially, this may occur along the length of already-flowing capillaries (i.e. longitudinal recruitment). Today, the capillary is still considered the principal site for O(2) and substrate delivery to contracting skeletal muscle. Indeed, the presence of very low intramyocyte O(2) partial pressures (PO(2)s) and the absence of intramyocyte PO(2) gradients, whilst refuting the relevance of diffusion distances, place an even greater importance on capillary hemodynamics. This emergent picture calls for a paradigm-shift in our understanding of the function of capillaries by de-emphasizing de novo'capillary recruitment'. Diseases such as heart failure impair blood-myocyte O(2) flux, in part, by decreasing the proportion of RBC-flowing capillaries. Knowledge of capillary function in healthy muscle is requisite for identification of pathology and efficient design of therapeutic treatments.

Exercise intensity and oxygen uptake kinetics in African-American and Caucasian women

The effect of exercise intensity on the on- and off-transient kinetics of oxygen uptake (VO(2)) was investigated in African American (AA) and Caucasian (C) women. African American (n = 7) and Caucasian (n = 6) women of similar age, body mass index and weight, performed an incremental test and bouts of square-wave exercise at moderate, heavy and very heavy intensities on a cycle ergometer. Gas exchange threshold (LT(GE)) was lower in AA (13.6 ± 2.3 mL kg(-1) min(-1)) than C (18.6 ± 5.6 mL kg(-1) min(-1)). The dynamic exercise and recovery VO(2) responses were characterized by mathematical models. There were no significant differences in (1) peak oxygen uptake (VO(2peak)) between AA (28.5 ± 5 mL kg(-1) min(-1)) and C (31.1 ± 6.6 mL kg(-1) min(-1)) and (2) VO(2) kinetics at any exercise intensity. At moderate exercise, the on- and off- VO(2) kinetics was described by a monoexponential function with similar time constants τ (1,on) (39.4 ± 12.5; 38.8 ± 15 s) and τ (1,off) (52.7 ± 10.1; 40.7 ± 4.4 s) for AA and C, respectively. At heavy and very heavy exercise, the VO(2) kinetics was described by a double-exponential function. The parameter values for heavy and very heavy exercise in the AA group were, respectively: τ (1,on) (47.0 ± 10.8; 44.3 ± 10 s), τ (2,on) (289 ± 63; 219 ± 90 s), τ (1,off) (45.9 ± 6.2; 50.7 ± 10 s), τ (2,off) (259 ± 120; 243 ± 93 s) while in the C group were, respectively: τ (1,on) (41 ± 12; 43.2 ± 15 s); τ (2, on) (277 ± 81; 215 ± 36 s), τ (1,off) (40.2 ± 3.4; 42.3 ± 7.2 s), τ (2,off) (215 ± 133; 228 ± 64 s). The on- and off-transients were symmetrical with respect to model order and dependent on exercise intensity regardless of race. Despite similar VO(2) kinetics, LT(GE) and gain of the VO(2) on-kinetics at moderate intensity were lower in AA than C. However, generalization to the African American and Caucasian populations is constrained by the small subject numbers.

Comparison of quantity of left ventricular scarring and remodeling by magnetic resonance imaging in patients with versus without diabetes mellitus and with coronary artery disease

Diabetic patients with coronary artery disease (CAD) are more likely to develop heart failure (HF) than nondiabetic patients, but the mechanism responsible is unclear. Evidence suggests that infarct size and accompanying remodeling may not explain this difference. We used cardiac magnetic resonance (CMR) imaging to compare degree of left ventricular (LV) myocardial scar and remodeling in diabetic and nondiabetic patients with CAD. We evaluated 85 patients (39 diabetic, 46 nondiabetic) who underwent coronary angiography showing obstructive CAD and CMR imaging within 6 months of each other. Myocardial scar was measured by late gadolinium enhancement on CMR imaging and was graded according to spatial and transmural extents on a semiquantitative scale. More diabetic than nondiabetic patients had HF (69% vs 43%, p <0.03); however, groups did not differ in total scar burden (0.94 ± 0.60 vs 1.17 ± 0.74, p = NS), spatial extent of scar, or extent of transmural scar. Diabetes remained an independent predictor of HF after adjustment for CAD and other variables. LV ejection fraction (36 ± 12% vs 37 ± 14%, p = NS) and end-diastolic volume (215 ± 56 vs 217 ± 76 ml, p = NS) were similar for diabetic and nondiabetic patients, respectively. In conclusion, although diabetic patients with CAD had a higher prevalence of HF than nondiabetic patients, there was no difference in myocardial scar, LV volume, or LV ejection fraction. These findings support the theory that mechanisms other than extent of myocardial injury and negative remodeling play a significant role in the development of HF in diabetic patients with CAD.

Effect of elastic-band-based resistance training on leg blood flow in elderly women

The age-related decline in basal limb blood flow appears to be related to the pathogenesis of metabolic syndrome, noninsulin-dependent diabetes, and cardiovascular disease. Resistance training improves basal limb blood flow and vascular conductance in middle-aged men and women, but it is unknown whether similar vascular effects of training occur in the elderly. This study aimed to examine the effects of a 12-week progressive resistance training program using elastic bands on basal leg blood flow, vascular conductance, and functional performance in postmenopausal elderly women. Sixteen healthy postmenopausal females (age, 67 ± 5 years) were randomly assigned to a control (n = 8) or resistance training (n = 8) group, where they underwent 2 supervised strength sessions per week for 12 weeks. Prior to and at completion of this 12-week period, functional and strength performance and leg haemodynamic responses were measured. The training intervention produced significant increases in basal leg blood flow (31%), vascular conductance (34%), and a significant reduction in cardiac work (i.e., rate pressure product) at rest, as well as significant improvements in the 3 functional ability tests performed (30-s bicep curl, 30-s sit to stand, and back scratch). Haemodynamic or functional performance responses were not altered after the 12 weeks in the control group. This study demonstrates that a resistance training program using elastic bands elicits significant improvements in basal leg blood flow in postmenopausal elderly women.

Older Type 2 diabetic males do not exhibit abnormal pulmonary oxygen uptake and muscle oxygen utilization dynamics during submaximal cycling exercise

There are reports of abnormal pulmonary oxygen uptake (V̇o2) and deoxygenated hemoglobin ([HHb]) kinetics in individuals with Type 2 diabetes (T2D) below 50 yr of age with disease durations of <5 yr. We examined the V̇o2 and muscle [HHb] kinetics in 12 older T2D patients with extended disease durations (age: 65 ± 5 years; disease duration 9.3 ± 3.8 years) and 12 healthy age-matched control participants (CON; age: 62 ± 6 years). Maximal oxygen uptake (V̇o2max) was determined via a ramp incremental cycle test and V̇o2 and [HHb] kinetics were determined during subsequent submaximal step exercise. The V̇o2max was significantly reduced ( P < 0.05) in individuals with T2D compared with CON (1.98 ± 0.43 vs. 2.72 ± 0.40 l/min, respectively) but, surprisingly, V̇o2 kinetics was not different in T2D compared with CON (phase II time constant: 43 ± 17 vs. 41 ± 12 s, respectively). The Δ[HHb]/ΔV̇o2 was significantly higher in T2D compared with CON (235 ± 99 vs. 135 ± 33 AU·l−1·min−1; P < 0.05). Despite a lower V̇o2max, V̇o2 kinetics is not different in older T2D compared with healthy age-matched control participants. The elevated Δ[HHb]/ΔV̇o2 in T2D individuals possibly indicates a compromised muscle blood flow that mandates a greater O2 extraction during exercise. Longer disease duration may result in adaptations in the O2 extraction capabilities of individuals with T2D, thereby mitigating the expected age-related slowing of V̇o2 kinetics.

TRC150094 attenuates progression of nontraditional cardiovascular risk factors associated with obesity and type 2 diabetes in obese ZSF1 rats

Chronic overnutrition and consequential visceral obesity is associated with a cluster of risk factors for cardiovascular disease and type 2 diabetes mellitus. Moreover, individuals who have a triad of hypertension, dysglycemia, and elevated triglycerides along with reduced high-density lipoprotein cholesterol have a greater residual cardiovascular risk even after factoring for the traditional risk factors such as age, smoking, diabetes, and elevated low-density lipoprotein cholesterol. In our previous study we demonstrated that TRC150094, when administered to rats receiving a high-fat diet, stimulated mitochondrial fatty acid oxidation (FAO) and reduced visceral adiposity, opening an interesting perspective for a possible clinical application. In the present study, oral administration of TRC150094 to obese Zucker spontaneously hypertensive fatty rats (obese ZSF1) improved glucose tolerance and glycemic profile as well as attenuated a rise in blood pressure. Obese ZSF1 rats treated with TRC150094 also showed reduced hepatic steatosis, reduced progression of nephropathy, and improved skeletal muscle function. At the cellular level, TRC150094 induced a significant increase in mitochondrial respiration as well as an increased FAO in liver and skeletal muscle, ultimately resulting in reduced hepatic as well as total body fat accumulation, as evaluated by magnetic resonance spectroscopy and magnetic resonance imaging, respectively. If reproduced in humans, these results could confirm that TRC150094 may represent an attractive therapeutic agent to counteract multiple residual cardiovascular risk components.

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.

Nitric oxide bioavailability modulates the dynamics of microvascular oxygen exchange during recovery from contractions

AIM

lowered microvascular PO(2) (PO(2) mv) during the exercise off-transient likely impairs muscle metabolic recovery and limits the capacity to perform repetitive tasks. The current investigation explored the impact of altered nitric oxide (NO) bioavailability on PO(2) mv during recovery from contractions in healthy skeletal muscle. We hypothesized that increased NO bioavailability (sodium nitroprusside: SNP) would enhance PO(2) mv and speed its recovery kinetics while decreased NO bioavailability (l-nitro arginine methyl ester: l-NAME) would reduce PO(2) mv and slow its recovery kinetics.

METHODS

  PO(2) mv was measured by phosphorescence quenching during transitions (rest-1 Hz twitch-contractions for 3 min-recovery) in the spinotrapezius muscle of Sprague-Dawley rats under SNP (300 microm), Krebs-Henseleit (CONTROL) and l-NAME (1.5 mm) superfusion conditions.

RESULTS

relative to recovery in CONTROL, SNP resulted in greater overall microvascular oxygenation as assessed by the area under the PO(2) mv curve (PO(2 AREA) ;

CONTROL

3471 ± 292 mmHg s; SNP: 4307 ± 282 mmHg s; P < 0.05) and faster off-kinetics as evidenced by the mean response time (MRToff;

CONTROL

60.2 ± 6.9 s; SNP: 34.8 ± 5.7 s; P < 0.05), whereas l-NAME produced lower PO(2 AREA) (2339 ± 444 mmHg s; P < 0.05) and slower MRToff (86.6 ± 14.5s; P < 0.05).

CONCLUSION

no bioavailability plays a key role in determining the matching of O(2) delivery-to-O(2) uptake and thus the upstream O(2) pressure driving capillary-myocyte O(2) flux (i.e. PO(2) mv) following cessation of contractions in healthy skeletal muscle. Additionally, these data support a mechanistic link between reduced NO bioavailability and prolonged muscle metabolic recovery commonly observed in ageing and diseased populations.

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.

Oxygen uptake kinetics during exercise in adults with Down syndrome

Persons with Down syndrome (DS) have diminished submaximal and peak work capacity. This study evaluated the dynamic response of oxygen uptake at onset and recovery (VO(2) kinetics) of constant-load exercise (moderate intensity 45% VO(2peak)) in adults with DS. A total of 27 healthy participants aged 18-50 years performed graded treadmill exercise to assess peak VO(2): 14 with DS (9 males and 5 females) and 13 controls without disabilities (9 males and 4 females). Subjects also performed constant-load exercise tests at 45% VO(2peak) to determine VO(2) on-transient and VO(2) off-transient responses. Peak VO(2) was lower in participants with DS as compared to controls (DS 30.2 ± 7.1; controls 46.1 ± 9.6 mL kg(-1) min(-1), P < 0.05). In contrast, at 45% VO(2peak), the time constants for the VO(2) on-transients (DS 34.6 ± 9.1; controls 37.6 ± 9.0 s) and VO(2) off-transients (DS 36.5 ± 12.3; controls 37.7 ± 7.0 s) were not significantly different between the groups. Additionally, there were no differences between on-transient and off-transient time constants in participants with DS or controls. These data demonstrate that the VO(2) kinetics at onset and recovery of moderate intensity exercise is similar between adults with DS and controls. Therefore, the submaximal exercise performance of these individuals is not affected by slowed VO(2) kinetics.

Effect of reduced total blood volume on left ventricular volumes and kinetics in type 2 diabetes

AIM

Although impaired left ventricular (LV) diastolic function is commonly observed in patients with type 2 diabetes, it remains unclear whether the impairment is caused by altered LV relaxation or changes in LV preload. The purpose of this study was to examine the influence of LV function and LV loading conditions on stroke volume in men with type 2 diabetes.

METHODS

Cardiac magnetic resonance imaging scans were performed in eight men with type 2 diabetes and 11 non-diabetic men matched for age, weight and physical activity level. Total blood volume was determined with the Evans blue dye dilution technique.

RESULTS

End-diastolic volume (EDV), the ratio of peak early to late mitral inflow velocity (E/A) and stroke volume were lower in men with type 2 diabetes than in non-diabetic individuals. Peak filling rate and peak ejection rate were not different between diabetic and non-diabetic individuals; however, men with type 2 diabetes had proportionally longer systolic duration than non-diabetic individuals. Heart rate was higher and total blood volume was lower in men with type 2 diabetes. The lower total blood volume was correlated with a lower EDV in men with type 2 diabetes.

CONCLUSIONS

Men with type 2 diabetes have an altered cardiac cycle and lower end-diastolic and stroke volume. A lower total blood volume and higher heart rate in men with type 2 diabetes suggest that changes in LV preload, independent of changes in LV relaxation or contractility, influence LV diastolic filling and stroke volume in this population.

Walking economy before and after the onset of claudication pain in patients with peripheral arterial disease

PURPOSE

To determine the walking economy before and after the onset of claudication pain in patients with peripheral arterial disease (PAD), and to identify predictors of the change in walking economy following the onset of claudication pain.

METHODS

A total of 39 patients with PAD were studied, in which 29 experienced claudication (Pain group) during a constant load, walking economy treadmill test (speed = 2.0 mph, grade = 0%) and 10 were pain-free during this test (Pain-Free group). Patients were characterized on walking economy (ie, oxygen uptake during ambulation), as well as on demographic characteristics, cardiovascular risk factors, baseline exercise performance measures, and the ischemic window calculated from the decrease in ankle systolic blood pressure following exercise.

RESULTS

During the constant load treadmill test, the Pain group experienced onset of claudication pain at 323 +/- 195 seconds (mean +/- standard deviation) and continued to walk until maximal pain was attained at 759 +/- 332 seconds. Walking economy during pain-free ambulation (9.54 +/- 1.42 ml x kg(-1) x min(-1)) changed (P < .001) after the onset of pain (10.18 +/- 1.56 ml x kg(-1) x min(-1)). The change in walking economy after the onset of pain was associated with ischemic window (P < .001), hypertension (P < .001), diabetes (P = .002), and height (P = .003). In contrast, the Pain-Free group walked pain-free for the entire 20-minute test duration without a change in walking economy (P = .36) from the second minute of exercise (9.20 +/- 1.62 ml x kg(-1) x min(-1)) to the nineteenth minute of exercise (9.07 +/- 1.54 ml x kg(-1) x min(-1)).

CONCLUSION

Painful ambulation at a constant speed is associated with impaired walking economy, as measured by an increase in oxygen uptake in patients limited by intermittent claudication, and the change in walking economy is explained, in part, by severity of PAD, diabetes, and hypertension.

Metabolic myopathies: functional evaluation by analysis of oxygen uptake kinetics

PURPOSE

The aim was to identify additional noninvasive tools allowing to detect and to quantify the metabolic impairment in patients with mitochondrial myopathies (MM) or McArdle's disease (McA).

METHODS

Kinetics of adjustment of pulmonary oxygen uptake (VO2 kinetics) during transitions to constant-load moderate-intensity cycle ergometer exercise were determined on 15 MM, 8 McA, 21 patients with signs and/or symptoms of metabolic myopathy but a negative biopsy ("patient controls"; P-CTRL), and 22 healthy untrained controls (CTRL).

RESULTS

VO2 kinetics were slower in MM and in McA versus P-CTRL and CTRL, slower in McA versus MM, and not significantly different between P-CTRL and CTRL. The time constants (tau) of the monoexponential function describing the VO2 kinetics were (X +/- SE) 59.2 +/- 8.5 s in MM, 87.6 +/- 16.4 s in McA, 36.9 +/- 3.1 s in P-CTRL, and 35.4 +/- 1.9 s in CTRL. In a subgroup of the patients (eight MM and seven McA), tau of VO2 kinetics were negatively correlated with two variables determined in a previous study (Grassi B, Marzorati M, Lanfranconi F, et al. Impaired oxygen extraction in metabolic myopathies: detection and quantification by near-infrared spectroscopy. Muscle Nerve. 2007;35:510-20): a) a muscle oxygenation index, obtained by near-infrared spectroscopy, estimating the peak capacity of skeletal muscle fractional O2 extraction; and b) VO2 peak.

CONCLUSIONS

In MM and McA patients, analysis of pulmonary VO2 kinetics during moderate-intensity exercise allows to identify and to quantify, noninvasively, the impairment of skeletal muscle oxidative metabolism. In these patients, the slower VO2 kinetics can be considered a marker of the impaired exercise tolerance. The present data could be useful for clinicians who need an objective, quantitative, and longitudinal evaluation of the impairment to be used in the follow-up of these patients as well as in the assessment of therapeutic interventions.

Insulin resistance in adolescents with type 1 diabetes and its relationship to cardiovascular function

CONTEXT

Cardiovascular disease is the major cause of death in adults with diabetes, yet little is specifically known about the effects of type 1 diabetes (T1D) on cardiovascular outcomes in youth. Although insulin resistance (IR) likely contributes to exercise and cardiovascular dysfunction in T2D, IR is not typically considered a contributor in T1D.

OBJECTIVE

We hypothesized that cardiopulmonary fitness would be reduced in T1D youth in association with IR and cardiovascular dysfunction.

DESIGN AND PARTICIPANTS

This cross-sectional study at an academic hospital included 12 T1D adolescents compared with 12 nondiabetic controls, similar in age, pubertal stage, activity level, and body mass index.

OUTCOME MEASURES

Cardiopulmonary fitness was measured by peak oxygen consumption (VO(2)peak) and oxygen uptake kinetics (VO(2)kinetics), IR by hyperinsulinemic clamp, cardiac function by echocardiography, vascular function by venous occlusion plethysmography, intramyocellular lipid by magnetic resonance spectroscopy, and body composition by dual-energy x-ray absorptiometry.

RESULTS

T1D adolescents had significantly decreased VO(2)peak, peak work rate, and insulin sensitivity compared with nondiabetic adolescents. T1D youth also had reduced vascular reactivity and evidence of diastolic dysfunction and left ventricular hypertrophy. Despite their IR and reduced cardiovascular fitness, T1D youth had paradoxically normal intramyocellular lipid, waist to hip ratio, and serum lipids and high adiponectin levels. In multivariate analysis, IR primarily, and forearm blood flow secondarily, independently predicted VO(2)peak.

CONCLUSIONS

T1D youth demonstrated IR, impaired functional exercise capacity and cardiovascular dysfunction. The phenotype of IR in T1D youth was unique, suggesting a pathophysiology that is different from T2D, yet may adversely affect long-term cardiovascular outcomes.

Women with type 2 diabetes perceive harder effort during exercise than nondiabetic women

Regular exercise is a cornerstone of diabetes treatment; however, people with type 2 diabetes (T2D) are commonly sedentary. It is possible that a harder rate of perceived exertion (RPE) during exercise for those with T2D as compared with nondiabetics may be a barrier to physical activity. This study examined RPE (Borg scale, ordinal range 6-20) during submaximal exercise at identical absolute work rates to test the hypothesis that women with T2D demonstrate harder RPE during exercise than nondiabetic controls. In a prespecified analysis of existing data from equivalently sedentary women, RPE during submaximal exercise was compared among women with uncomplicated T2D (n = 13, mean body mass index (BMI) 34.2, mean hemoglobin A1c 9%), overweight controls (OC, n = 13, mean BMI 30.7), and normal-weight controls (NWC, n = 13, mean BMI 23.1). Subjects performed three 7 min, constant-load exercise tests at 20 W and 30 W. Mixed-effects general linear modeling was used to test for differences in mean RPE estimates among groups with and without adjustment for relative work intensity, age, habitual physical activity, or BMI. Subjects with T2D perceived harder effort during bicycling exercise than controls, as measured by RPE at 20 W and 30 W (p < 0.05 for T2D vs. OC and for T2D vs. NWC). Adjusting for relative work intensity eliminated significant group RPE differences at 30 W, but group RPE differences at 20 W remained significant. Harder perceived effort during exercise may be a barrier to physical activity for those with T2D.

Exercise therapy in type 2 diabetes

Structured exercise is considered an important cornerstone to achieve good glycemic control and improve cardiovascular risk profile in Type 2 diabetes. Current clinical guidelines acknowledge the therapeutic strength of exercise intervention. This paper reviews the wide pathophysiological problems associated with Type 2 diabetes and discusses the benefits of exercise therapy on phenotype characteristics, glycemic control and cardiovascular risk profile in Type 2 diabetes patients. Based on the currently available literature, it is concluded that Type 2 diabetes patients should be stimulated to participate in specifically designed exercise intervention programs. More attention should be paid to cardiovascular and musculoskeletal deconditioning as well as motivational factors to improve long-term treatment adherence and clinical efficacy. More clinical research is warranted to establish the efficacy of exercise intervention in a more differentiated approach for Type 2 diabetes subpopulations within different stages of the disease and various levels of co-morbidity.

Insulin resistance in adolescents with type 2 diabetes is associated with impaired exercise capacity

CONTEXT

The incidence of pediatric type 2 diabetes (T2D) is rising, with unclear effects on the cardiovascular system. Cardiopulmonary fitness, a marker of morbidity and mortality, is abnormal in adults with T2D, yet the mechanisms are incompletely understood.

OBJECTIVE

We hypothesized that cardiopulmonary fitness would be reduced in youth with T2D in association with insulin resistance (IR) and cardiovascular dysfunction.

DESIGN, SETTING, AND PARTICIPANTS

We conducted a cross-sectional study at an academic hospital that included 14 adolescents (age range, 12-19 yr) with T2D, 13 equally obese adolescents and 12 lean adolescents similar in age, pubertal stage, and activity level.

MAIN OUTCOME MEASURES

Cardiopulmonary fitness was measured by peak oxygen consumption (VO(2)peak) and oxygen uptake kinetics (VO(2)kinetics), IR by hyperinsulinemic clamp, cardiac function by echocardiography, vascular function by venous occlusion plethysmography, body composition by dual-energy x-ray absorptiometry, intramyocellular lipid by magnetic resonance spectroscopy, and inflammation by serum markers.

RESULTS

Adolescents with T2D had significantly decreased VO(2)peak and insulin sensitivity, and increased soleus intramyocellular lipid, C-reactive protein, and IL-6 compared to obese or lean adolescents. Adolescents with T2D also had significantly prolonged VO(2)kinetics, decreased work rate, vascular reactivity, and adiponectin, and increased left ventricular mass and fatty acids compared to lean adolescents. In multivariate linear regression analysis, IR primarily, and fasting free fatty acids and forearm blood flow secondarily, were significant independent predictors of VO(2)peak.

CONCLUSIONS

Given the strong relationship between decreased cardiopulmonary fitness and increased mortality, these findings in children are especially concerning and represent early signs of impaired cardiac function.

Cardiac dysfunction during exercise in uncomplicated type 2 diabetes

PURPOSE

Type 2 diabetes mellitus (T2DM) has been associated with reduced peak exercise capacity (VO(2peak)). The causes of this impairment are not clearly established, but evidence suggests that abnormalities in cardiac function play a significant role. We hypothesized that exercise would be associated with impaired cardiac function and hemodynamics in recently diagnosed T2DM, even in the absence of clinically evident cardiovascular complications.

METHODS

After baseline normal echocardiography screening, 10 premenopausal women with uncomplicated T2DM (average duration of diagnosed T2DM, 3.6 yr) and 10 healthy nondiabetic women of similar age, weight, and activity levels performed a peak cardiopulmonary exercise test while instrumented with an indwelling pulmonary artery catheter for assessing cardiac function. On separate days, technetium-99m sestamibi (cardolite) imaging was performed to assess myocardial perfusion at rest and peak exercise in seven T2DM and seven control patients.

RESULTS

Resting measures of cardiac hemodynamics were similar in T2DM and control subjects. Absolute VO(2peak) (mL x min(-1)) and peak cardiac output (L x min(-1)) tended to be lower in T2DM than in control subjects but did not reach statistical significance. However, pulmonary capillary wedge pressure (PCWP) rose significantly more during exercise in T2DM than in controls (148% vs 109% increase at peak exercise, P < 0.01). Normalized myocardial perfusion index was lower in persons with diabetes than in controls (11.0 +/- 3.5 x e(-9) vs 17.5 +/- 8.1 x e(-9), respectively, P < 0.05) and inversely related to peak exercise PCWP (R = -0.56, P < 0.05).

CONCLUSIONS

Cardiac hemodynamics during graded exercise are altered in women with recently diagnosed T2DM as demonstrated by the disproportionate increase in PCWP at peak exercise compared with controls subjects. Cardiac abnormalities observed are potentially early signs of subclinical cardiac dysfunction associated with T2DM, which may precede the more greatly impaired cardiac function at rest and with exercise observed in longer established T2DM.

Maximal lipid oxidation in patients with type 2 diabetes is normal and shows an adequate increase in response to aerobic training

AIM

Insulin resistance in subjects with type 2 diabetes (T2D) and obesity is associated with an imbalance between the availability and the oxidation of lipids. We hypothesized that maximal whole-body lipid oxidation during exercise (FATmax) is reduced and that training-induced metabolic adaptation is attenuated in T2D.

METHODS

Obese T2D (n = 12) and control (n = 11) subjects matched for age, sex, physical activity and body mass index completed 10 weeks of aerobic training. Subjects were investigated before and after training with maximal and submaximal exercise tests and euglycaemic-hyperinsulinaemic clamps combined with muscle biopsies.

RESULTS

Training increased maximal oxygen consumption (VO(2max)) and muscle citrate synthase activity and decreased blood lactate concentrations during submaximal exercise in both groups (all p < 0.01). FATmax increased markedly (40-50%) in both T2D and control subjects after training (all p < 0.001). There were no significant differences in these variables and lactate threshold (%VO(2max)) between groups before or after training. Insulin-stimulated glucose disappearance rate (Rd) was lower in T2D vs. control subjects both before and after training. Rd increased in response to training in both groups (all p < 0.01). There was no correlation between Rd and measures of oxidative capacity or lipid oxidation during exercise or the training-induced changes in these parameters.

CONCLUSIONS

FATmax was not reduced in T2D, and muscle oxidative capacity increased adequately in response to aerobic training in obese subjects with and without T2D. These metabolic adaptations to training seem to be unrelated to changes in insulin sensitivity and indicate that an impaired capacity for lipid oxidation is not a major cause of insulin resistance in T2D.

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.

Impact of metformin on peak aerobic capacity

Individually, exercise and the drug metformin have been shown to prevent or delay type 2 diabetes. Metformin mildly inhibits complex I of the electron transport system and may impact aerobic capacity in people exercising while taking metformin. The purpose of the study was to evaluate the effects of metformin on maximal aerobic capacity in healthy individuals without mitochondrial dysfunction. Seventeen healthy, normal-weight men (n=11) and women (n=6) participated in a double-blind, placebo-controlled, cross-over design. Peak aerobic capacity was measured twice using a continuous, incrementally graded protocol; once after 7-9 d of metformin (final dose=2000 mg/d) and once with placebo, with 1 week between tests. The order of the conditions was counterbalanced. Peak oxygen uptake (VO2 peak), heart rate (HR), ventilation (VE), respiratory exchange ratio (RER), rating of perceived exertion (RPE), and test duration were compared across conditions using paired t tests with the R statistical program. VO2 peak (-2.7%), peak heart rate (-2.0%), peak ventilation (-6.2%), peak RER (-3.0%), and exercise duration (-4.1%) were all reduced slightly, but significantly, with metformin (all p<0.05). There was no effect of metformin on RPE or ventilatory breakpoint. Correlations between the decrement in VO2 peak and any of the other outcome variables were weak (r2<0.20) and not significant. Short-term treatment with metformin has statistically significant, but physiologically subtle, effects that reduce key outcomes related to maximal exercise capacity. Whether this small but consistent effect is manifested in people with insulin resistance or diabetes who already have some degree of mitochondrial dysfunction remains to be determined.

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.

Exercise calorimetry in sedentary patients: procedures based on short 3 min steps underestimate carbohydrate oxidation and overestimate lipid oxidation

OBJECTIVES

Among exercise calorimetry tests designed for calculating the respective part of carbohydrates and lipids oxidized at exercise, some use 6 min steps and others use 3 min steps. Is this last method, which has been validated in healthy subjects, still accurate in very sedentary patients, who need more time to reach a steady state in respiratory gas exchanges?

METHODS

We compared data obtained with calorimetry (RER and indicators of substrate oxidation) performed on the 2nd-3rd min and the 5th-6th min of each step of a protocol using four 6-min submaximal steps in 17 sedentary subjects (mean age: 51 years) including seven type 2 diabetics and six obese persons.

RESULTS

Respiratory exchange ratio (RER) measured with the 3 min steps procedure are well correlated with the 6 min procedure in sedentary patients (r=0.928). However, a Bland-Altman analysis indicated an average underestimation of RER with 3 min steps (-0.0138). Moreover, we observed an average underestimation of carbohydrate oxidation rates of 70.1 mg/min with the 3 min steps procedure. On the contrary, as to lipid oxidation, we measured an average overestimation of 16.2 mg/min. Furthermore, carbohydrate and lipid oxidation rates measured with the 3 min steps procedure are well correlated with the 6 min steps procedure. Moreover, there was an average overestimation of the point at cross over with 3 min steps (+3.29 Watts). For lipox max point (power at which the increase in lipid oxidation induced by the increasing workload reaches a maximum), we observed an average underestimation with 3 min steps (-1.88 Watt). Although the differences between respectively mean values in cross over point and lipox max point between the two protocols are weak, a Bland-Altman analysis indicated more relevant discrepancies in many subjects between the two protocols.

CONCLUSION

In very sedentary patients undergoing such tests for targeting exercise prescription, the 3-min procedure appears to be too short for performing an accurate calorimetry and we rather recommend the protocol using 6-min steps.

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.

Pulmonary O2 uptake on-kinetics in sprint- and endurance-trained athletes

Pulmonary O2 uptake kinetics during "step" exercise have not been characterized in young, sprint-trained (SPT), athletes. Therefore, the objective of this study was to test the hypotheses that SPT athletes would have (i) slower phase II kinetics and (ii) a greater oxygen uptake "slow component" when compared with endurance-trained (ENT) athletes. Eight sub-elite SPT athletes (mean (+/-SD) age=25 (+/-7) y; mass=80.3 (+/-7.3) kg) and 8 sub-elite ENT athletes (age=28 (+/-4) y; mass=73.2 (+/-5.1) kg) completed a ramp incremental cycle ergometer test, a Wingate 30 s anaerobic sprint test, and repeat "step" transitions in work rate from 20 W to moderate- and severe-intensity cycle exercise, during which pulmonary oxygen uptake was measured breath by breath. The phase II oxygen uptake kinetics were significantly slower in the SPT athletes both for moderate (time constant, tau; SPT 32 (+/-4) s vs. ENT 17 (+/-3) s; p<0.01) and severe (SPT 32 (+/-12) s vs. ENT 20 (+/-6) s; p<0.05) exercise. The amplitude of the slow component (derived by exponential modelling) was not significantly different between the groups (SPT 0.55 (+/-0.12) L.min(-1) vs. ENT 0.50 (+/-0.22) L.min(-1)), but the increase in oxygen uptake between 3 and 6 min of severe exercise was greater in the SPT athletes (SPT 0.37 (+/-0.08) L.min(-1) vs. ENT 0.20 (+/-0.09) L.min(-1); p<0.01). The phase II tau was significantly correlated with indices of aerobic exercise performance (e.g., peak oxygen uptake (moderate-intensity r=-0.88, p<0.01; severe intensity r=-0.62; p<0.05), whereas the relative amplitude of the oxygen uptake slow component was significantly correlated with indices of anaerobic exercise performance (e.g., Wingate peak power output; r=0.77; p<0.01). Thus, it could be concluded that sub-elite SPT athletes have slower phase II oxygen uptake kinetics and a larger oxygen uptake slow component compared with sub-elite ENT athletes. It appears that indices of aerobic and anaerobic exercise performance differentially influence the fundamental and slow components of the oxygen uptake kinetics.

Effect of type 2 diabetes mellitus on exercise intolerance and the physiological responses to exercise in peripheral arterial disease

AIMS/HYPOTHESIS

There are conflicting data about the effect of type 2 diabetes mellitus on exercise tolerance in peripheral arterial disease. To elucidate this problem, we compared the tolerance and physiological responses to treadmill and cycle exercise in 31 patients with peripheral arterial disease and intermittent claudication.

MATERIALS AND METHODS

One group of these patients had type 2 diabetes (n = 12) and its members were matched for sex and age with a group of patients who did not have diabetes (n = 12). Since BMI and body weight were greater in the diabetic group (28.4 +/- 3.7 vs 25.2 +/- 2.4 kg/m(2); 84.0 +/- 14.6 vs 73.8 +/- 8.0 kg), we also studied a third, 'heavy' group of non-diabetic patients with claudication of similar age (n = 7; BMI = 30.9 +/- 5.3 kg/m(2); body weight = 85.2 +/- 8.2 kg).

RESULTS

Compared with the 'light' non-diabetic group, maximum treadmill times were shorter for the diabetic and heavy non-diabetic groups (1,448 vs 845 and 915 s; ANOVA p = 0.01); maximum cycle time also tended to be shorter (ANOVA, p = 0.08) in the diabetic and heavy non-diabetic groups (median = 1,231 vs 730 and 797 s). The majority of physiological responses assessed were not different between the groups, although the time constant of oxygen uptake during submaximal treadmill and cycle exercise was significantly larger (ANOVA p < 0.05) for the diabetic group.

CONCLUSIONS/INTERPRETATION

These data demonstrate that exercise tolerance is lower in diabetic than non-diabetic patients with claudication, but that this difference is due to obesity rather than diabetes itself.

Lactate and ventilatory thresholds in type 2 diabetic women

Anaerobic threshold (AT) has been considered the optimal exercise intensity for type 2 diabetes mellitus (DM 2) patients, but there is little information about the comparison between lactate (LT) and ventilatory (VT) thresholds in this population, particularly during treadmill exercise. Therefore, we evaluated DM 2 women in order to compare and analyze the relationships between VT and LT intensities. Fifteen women with DM 2 without complications and comorbidities (50.7 +/- 8.0 years; 71.3 +/- 8.6 kg; 154 +/- 5 cm; 37.8 +/- 3.9% fat; 4.7 +/- 3.2 years of disease diagnose and 138 +/- 45 mg/dl fasting glucose) were subjected to a graded treadmill test-initial velocity and increments of 1 km/h every 2 min until voluntary exhaustion. VT was determined from V(E)/V(O(2)) and V(E)-V(CO(2)) ratios and LT was defined as the point at which a first increase in blood lactate occurs during incremental test. Our results showed no significant differences (p > 0.05) and significant correlations between VT and LT expressed in velocity (4.7 +/- 0.7 versus 4.6 +/- 0.7 km/h, r = 0.62), absolute V(O(2)) (1.27 +/- 0.33 versus 1.24 +/- 0.28 l min(-1), r = 0.93); relative V(O(2)) (18.3 +/- 5.7 versus 17.6 +/- 4.6 ml kg(-1) min(-1), r = 0.84) and %V(O(2)(max)) (80 +/- 12 versus 78 +/- 10%, r = 0.82). These results suggest that both VT and LT can be used to access AT in DM 2 women during graded treadmill exercise.

Advanced Glycation End Product in Diabetic Rat Skeletal Muscle in vivo

BACKGROUND

Advanced glycation end products (AGEs) are implicated in the etiology of diabetic complications in the kidney, nerve and eye. Skeletal muscle contractile parameters have also been found to be altered in diabetes. Glycation has not been extensively studied in skeletal muscle, but AGE-modified proteins may influence contractility.

OBJECTIVE AND METHODS

The aim of this study was to use immunohistochemistry to identify distribution patterns of the AGE Nepsilon-(carboxymethyl)-lysine in plantaris muscle of diabetic rats.

RESULTS

Results revealed the presence of Nepsilon-(carboxymethyl)-lysine intracellularly and also at sites along the myofiber periphery. The number of myofibers immunolabeling for AGE in animals with diabetes was more than 4-fold greater than in control animals. Additionally, there was a greater proportion of slow + fast myosin heavy chain coexpression in the AGE-positive cells from diabetic animals than in AGE-positive fibers from control animals. No significant difference was present between cross-sectional areas of AGE-positive fibers and AGE-negative fibers within the respective experimental groups.

CONCLUSIONS

AGE accumulation is greater in skeletal muscle in vivo from diabetic animals than in control animals. This AGE accumulation appears to be associated with fiber-type transformation rather than with myofiber size. Further study is needed to determine the identity of these AGE-modified proteins and to determine how they influence skeletal muscle function in diabetes.

Vitamin C improves basal metabolic rate and lipid profile in alloxan-induced diabetes mellitus in rats

Diabetes mellitus (DM)is a multi-factorial disease which is characterized by hyperglycaemia, lipoprotein abnormalities and oxidative stress. This study evaluated effect of oral vitamin C administration on basal metabolic rate and lipid profile of alloxan-induced diabetic rats. Vitamin C was administered at 200 mg/kg body wt. by gavage for four weeks to diabetic rats after which the resting metabolic rate and plasma lipid profile was determined. The results showed that vitamin C administration significantly (p less than 0.01) reduced the resting metabolic rate in diabetic rats; and also lowered plasma triglyceride, total cholesterol and low-density lipoprotein cholesterol. These results suggest that the administration of vitamin C in this model of established diabetes mellitus might be beneficial for the restoration of basal metabolic rate and improvement of lipid profile. This may at least in part reduce the risk of cardiovascular events seen in diabetes mellitus.

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.

Elevated peak exercise systolic blood pressure is not associated with reduced exercise capacity in subjects with Type 2 diabetes

Subjects with Type 2 diabetes without cardiovascular disease have a reduced exercise capacity compared with nondiabetic subjects. However, the mechanisms responsible for this phenomenon are unknown. The purpose of this study was to evaluate the impact of exercise systolic blood pressure (SBP) response on diverse exercise tolerance parameters in Type 2 diabetic subjects. Twenty-eight sedentary men with Type 2 diabetes were recruited for this study. Subjects were treated with oral hypoglycemic agents and/or diet. Evaluation of glycemic control and peak exercise capacity were performed for each subject. The subjects were divided into two groups according to the median value of peak SBP (210 mmHg) measured in each subject. We observed a 13, 13, and 16% reduction in the relative peak oxygen uptake (V̇o2 peak), absolute V̇o2 peak, and peak work rate in the low- compared with the high-peak SBP group [26.95 (SD 5.35) vs. 30.96 (SD 3.61) ml·kg−1·min−1, 2.5 (SD 0.4) vs. 2.8 (SD 0.6) l/min, and 169 (SD 34) vs. 202 (SD 32) W; all P < 0.05]. After adjusting for age, relative V̇o2 peak was still significantly different ( P < 0.05). There were similar peak respiratory exchange ratio (RER) [1.20 (SD 0.08) vs. 1.16 (SD 0.07); P = 0.24] and peak heart rate [160 (SD 20) vs. 169 (SD 15) beats/min; P = 0.18] between the low- compared with the high-SBP group. No difference in glycemic control was observed between the two groups. The results reported in this study suggest that in subjects with Type 2 diabetes without cardiovascular disease, an elevated exercise SBP is not associated with reduced exercise capacity and its modulation is probably not related to glycemic control.

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.

Downhill treadmill running trains the rat spinotrapezius muscle

There are currently no models of exercise that recruit and train muscles, such as the rat spinotrapezius, that are suitable for transmission intravital microscopic investigation of the microcirculation. Recent experimental evidence supports the concept that running downhill on a motorized treadmill recruits the spinotrapezius muscle of the rat. Based on these results, we tested the hypothesis that 6 wk of downhill running (-14 degrees grade) for 1 h/day, 5 days/wk, at a speed of up to 35 m/min, would 1) increase whole body peak oxygen uptake (Vo(2 peak)), 2) increase spinotrapezius citrate synthase activity, and 3) reduce the fatigability of the spinotrapezius during electrically induced 1-Hz submaximal tetanic contractions. Trained rats (n = 6) elicited a 24% higher Vo(2 peak) (in ml.min(-1).kg(-1): sedentary 58.5 +/- 2.0, trained 72.7 +/- 2.0; P < 0.001) and a 41% greater spinotrapezius citrate synthase activity (in mumol.min(-1).g(-1): sedentary 14.1 +/- 0.7, trained 19.9 +/- 0.9; P < 0.001) compared with sedentary controls (n = 6). In addition, at the end of 15 min of electrical stimulation, trained rats sustained a greater percentage of the initial tension than their sedentary counterparts (control 34.3 +/- 3.1%, trained 59.0 +/- 7.2%; P < 0.05). These results demonstrate that downhill running is successful in promoting training adaptations in the spinotrapezius muscle, including increased oxidative capacity and resistance to fatigue. Since the spinotrapezius muscle is commonly used in studies using intravital microscopy to examine microcirculatory function at rest and during contractions, our results suggest that downhill running is an effective training paradigm that can be used to investigate the mechanisms for improved microcirculatory function following exercise training in health and disease.

Noninvasive Evaluation of Skeletal Muscle Oxidative Metabolism after Heart Transplant

PURPOSE

The main aim of the present study was to investigate skeletal muscle oxidative metabolism in heart transplant recipients (HTR) by noninvasive tools.

METHODS

Twenty male HTR (age 50.4 +/- 2.6 yr; mean +/- SE) and 17 healthy untrained age-matched controls (CTRL) performed an incremental exercise (IE) and a series of constant-load (CLE) moderate-intensity exercise tests on a cycloergometer. The following variables were determined: heart rate (HR); breath-by-breath pulmonary O2 uptake (VO2); and skeletal muscle (vastus lateralis) oxygenation indices by continuous-wave near-infrared spectroscopy. Changes in concentration of deoxygenated hemoglobin (Hb) and myoglobin (Mb) (Delta[deoxy(Hb + Mb)]), expressed as a fraction of values obtained during a transient limb ischemia, were taken as an index of skeletal muscle O2 extraction. "Peak" values were determined at exhaustion during IE. Kinetics of adjustment of variables were determined during CLE.

RESULTS

VO2peak, HRpeak, and Delta[deoxy(Hb + Mb)] peak were significantly lower in HTR than in CTRL (17.1 +/- 0.7 vs 34.0 +/- 1.9 mL.kg(-1).min(-1), 133.8 +/- 3.8 vs 173.0 +/- 4.8 bpm, and 0.42 +/- 0.03 vs 0.58 +/- 0.04, respectively). In HTR, Delta[deoxy(Hb + Mb)] increase at submaximal workloads was steeper than in CTRL, suggesting an impaired O2 delivery to skeletal muscles, whereas the lower Delta[deoxy(Hb + Mb)] peak values suggest an impaired capacity of O2 extraction at peak exercise. VO2 and HR kinetics during CLE were significantly slower in HTR than in CTRL, whereas, unexpectedly, no significant differences were found for Delta[deoxy(Hb+Mb)] kinetics (mean response time: 21.3 +/- 1.1 vs 20.2 +/- 1.2 s).

CONCLUSION

The findings confirm the presence of both "central" (cardiovascular) and "peripheral" (at the skeletal muscle level) impairments to oxidative metabolism in HTR. The noninvasiveness of the measurements will allow for serial evaluation of the patients, in the presence and/or absence of rehabilitation programs.

Impact of exercise training on insulin sensitivity, physical fitness, and muscle oxidative capacity in first-degree relatives of type 2 diabetic patients

First-degree relatives of type 2 diabetic patients (offspring) are often characterized by insulin resistance and reduced physical fitness (VO2 max). We determined the response of healthy first-degree relatives to a standardized 10-wk exercise program compared with an age-, sex-, and body mass index-matched control group. Improvements in VO2 max (14.1 +/- 11.3 and 16.1 +/- 14.2%; both P < 0.001) and insulin sensitivity (0.6 +/- 1.4 and 1.0 +/- 2.1 mg x kg(-1) x min(-1); both P < 0.05) were comparable in offspring and control subjects. However, VO2 max and insulin sensitivity in offspring were not related at baseline as in the controls (r = 0.009, P = 0.96 vs. r = 0.67, P = 0.002). Likewise, in offspring, exercise-induced changes in VO2 max did not correlate with changes in insulin sensitivity as opposed to controls (r = 0.06, P = 0.76 vs. r = 0.57, P = 0.01). Skeletal muscle oxidative capacity tended to be lower in offspring at baseline but improved equally in both offspring and controls in response to exercise training (delta citrate synthase enzyme activity 26 vs. 20%, and delta cyclooxygenase enzyme activity 25 vs. 23%. Skeletal muscle fiber morphology and capillary density were comparable between groups at baseline and did not change significantly with exercise training. In conclusion, this study shows that first-degree relatives of type 2 diabetic patients respond normally to endurance exercise in terms of changes in VO2 max and insulin sensitivity. However, the lack of a correlation between the VO2 max and insulin sensitivity in the first-degree relatives of type 2 diabetic patients indicates that skeletal muscle adaptations are dissociated from the improvement in VO2 max. This could indicate that, in first-degree relatives, improvement of insulin sensitivity is dissociated from muscle mitochondrial functions.

Effects of arterial hypotension on microvascular oxygen exchange in contracting skeletal muscle

In healthy animals under normotensive conditions (N), contracting skeletal muscle perfusion is regulated to maintain microvascular O2 pressures (Pmv[Formula: see text]) at levels commensurate with O2 demands. Hypovolemic hypotension (H) impairs muscle contractile function; we tested whether this condition would alter the matching of O2 delivery (Q̇o2) to O2 utilization (V̇o2), as determined by Pmv[Formula: see text] at the onset ofmuscle contractions. Pmv[Formula: see text] in the spinotrapezius muscles of seven female Sprague-Dawley rats (280 ± 6 g) was measured every 2 s across the transition from rest to 1-Hz twitch contractions. Measurements were made under N (mean arterial pressure, 97 ± 4 mmHg) and H (induced by arterial section; mean arterial pressure, 58 ± 3 mmHg, P < 0.05) conditions; Pmv[Formula: see text] profiles were modeled using a multicomponent exponential fitted with independent time delays. Hypotension reduced muscle blood flow at rest (24 ± 8 vs. 6 ± 1 ml−1·min−1·100 g−1 for N and H, respectively; P < 0.05) and during contractions (74 ± 20 vs. 22 ± 4 ml−1·min−1·100 g−1 for N and H, respectively; P < 0.05). H significantly decreased resting Pmv[Formula: see text] and steady-state contracting Pmv[Formula: see text](19.4 ± 2.4 vs. 8.7 ± 1.6 Torr for N and H, respectively, P < 0.05). At the onset of contractions, H reduced the time delay (11.8 ± 1.7 vs. 5.9 ± 0.9 s for N andH, respectively, P < 0.05) before the fall in Pmv[Formula: see text] and accelerated therate of Pmv[Formula: see text] decrease (time constant, 12.6 ± 1.4 vs. 7.3 ± 0.9 s for N and H, respectively, P < 0.05). Muscle V̇o2 was reduced by 71% at rest and 64% with contractions in H vs. N, and O2 extraction during H averaged 78% at rest and 94% during contractions vs. 51 and 78% in N. These results demonstrate that H constrains the increase of skeletal muscle Q̇o2 relative to that of V̇o2 at the onset of contractions,leading to a decreased Pmv[Formula: see text]. According to Fick's law, this scenario will decrease blood-myocyte O2 flux, thereby slowing V̇o2 kinetics and exacerbating the O2 deficit generated at exercise onset.

Effects of altered nitric oxide availability on rat muscle microvascular oxygenation during contractions

AIM

To explore the role of nitric oxide (NO) in controlling microvascular O2 pressure (P(O2)mv) at rest and during contractions (1 Hz). We hypothesized that at the onset of contractions sodium nitroprusside (SNP) would raise P(O2)mv and slow the kinetics of P(O2)mv change whereas l-nitro arginine methyl ester (L-NAME) would decrease P(O2)mv and speed its kinetics.

METHODS

We superfused the spinotrapezius muscle of female Sprague-Dawley rats (n = 7, body mass = 298 +/- 10 g) with SNP (300 microM) and L-NAME (1.5 mm) and measured P(O2)mv (phosphorescence quenching) during contractions.

RESULTS

SNP decreased mean arterial pressure (92 +/- 5 mmHg) below that of control (CON, 124 +/- 4 mmHg) and L-NAME (120 +/- 4 mmHg) conditions. SNP did not raise P(O2)mv at rest but it did elevate the P(O2)mv-to-MAP ratio (50% increase, P < 0.05) and slow the kinetics by lengthening the time-delay (TD, 14.0 +/- 5.0 s) and time constant (tau, 24.0 +/- 10.0 s) of the response compared with CON (TD, 8.4 +/- 3.3 s; tau, 16.0 +/- 4.5 s, P < 0.05 vs. SNP). L-NAME decreased P(O2)mv at rest and tended to speed tau (10.1 +/- 3.8 s, P = 0.1), while TD (8.1 +/- 1.0 s) was not significantly different. L-NAME also caused P(O2)mv to fall transiently below steady-state contracting values.

CONCLUSIONS

These results indicate that NO availability can significantly affect P(O2)mv at rest and during contractions and suggests that P(O2)mv derangements in ageing and chronic disease conditions may potentially result from impairments in NO availability.