The carbon monoxide prodrug oCOm-21 increases Ca2+ sensitivity of the cardiac myofilament

Patients undergoing cardiopulmonary bypass procedures require inotropic support to improve hemodynamic function and cardiac output. Current inotropes such as dobutamine, can promote arrhythmias, prompting a demand for improved inotropes with little effect on intracellular Ca2+ flux. Low-dose carbon monoxide (CO) induces inotropic effects in perfused hearts. Using the CO-releasing pro-drug, oCOm-21, we investigated if this inotropic effect results from an increase in myofilament Ca2+ sensitivity. Male Sprague Dawley rat left ventricular cardiomyocytes were permeabilized, and myofilament force was measured as a function of -log [Ca2+ ] (pCa) in the range of 9.0-4.5 under five conditions: vehicle, oCOm-21, the oCOm-21 control BP-21, and levosimendan, (9 cells/group). Ca2+ sensitivity was assessed by the Ca2+ concentration at which 50% of maximal force is produced (pCa50 ). oCOm-21, but not BP-21 significantly increased pCa50 compared to vehicle, respectively (pCa50 5.52 vs. 5.47 vs. 5.44; p < 0.05). No change in myofilament phosphorylation was seen after oCOm-21 treatment. Pretreatment of cardiomyocytes with the heme scavenger hemopexin, abolished the Ca2+ sensitizing effect of oCOm-21. These results support the hypothesis that oCOm-21-derived CO increases myofilament Ca2+ sensitivity through a heme-dependent mechanism but not by phosphorylation. Further analyses will confirm if this Ca2+ sensitizing effect occurs in an intact heart.

Treadmill running increases the calcium sensitivity of myofilaments in diabetic rats

The cardiovascular benefits of regular exercise are unequivocal, yet patients with type 2 diabetes respond poorly to exercise due to a reduced cardiac reserve. The contractile response of diabetic cardiomyocytes to beta-adrenergic stimulation is attenuated, which may result in altered myofilament calcium sensitivity and post-translational modifications of cardiac troponin I (cTnI). Treadmill running increases myofilament calcium sensitivity in non‑diabetic rats, and thus we hypothesized that endurance training would increase calcium sensitivity of diabetic cardiomyocytes and alter site-specific phosphorylation of cTnI. Calcium sensitivity, or pCa₅₀, was measured in Zucker Diabetic Fatty (ZDF) non-diabetic (nDM) and diabetic (DM) rat hearts after 8 weeks of either a sedentary (SED) or progressive treadmill running (TR) intervention. Skinned cardiomyocytes were connected to a capacitance-gauge transducer and a torque motor to measure force as a function of pCa (‑log[Ca²⁺]). Specific phospho-sites on cTnI and O‑GlcNAcylation were quantified by immunoblot and total protein phosphorylation by fluorescent gel staining (ProQ Diamond). The novel finding in this study was that training increased pCa₅₀ in both DM and nDM cardiomyocytes (p = 0.009). Phosphorylation of cTnI amino acid residues Ser23/24, a crucial protein kinase A site, and Threonine (Thr)144, was lower in DM hearts, but there was no effect of training on site-specific phosphorylation. Additionally, total phosphorylation and O-GlcNAcylation levels were not different between SED and TR groups. These findings suggest that regular exercise may benefit the diabetic heart by specifically targeting myofilament contractile function.

Short-term High-Intensity Interval Training Improves Fitness Before Surgery: A Randomised Clinical Trial

PURPOSE

Improving cardiopulmonary reserve, or peak oxygen consumption( V ˙ O_2peak ), may reduce postoperative complications, however this may be difficult to achieve between diagnosis and surgery. Our primary aim was to assess the efficacy of an approximate 14-session, preoperative High Intensity Interval Training(HIIT) program to increase V ˙ O_2peak by a clinically-relevant 2 mL·kg^-1 ·min^-1 . Our secondary aim was to document clinical outcomes.

METHODOLOGY

In this prospective study, participants aged 45-85 undergoing major abdominal surgery were randomised to standard care or 14 sessions of HIIT over 4 weeks. HIIT sessions involved approximately thirty minutes of stationary cycling. Interval training alternated one minute of high (with the goal of reaching 90% max heart rate at least once during the session) and low/moderate intensity cycling. Cardiopulmonary exercise testing(CPET) measured the change in V ˙ O_2peak from baseline to surgery. Clinical outcomes included postoperative complications, length of stay(LOS) and Short Form-36 quality of life questionnaire(SF-36).

RESULTS

Of 63 participants, 46 completed both CPETs and 50 completed clinical follow-up. There was a significant improvement in the HIIT group's mean ± SD V ˙ O_2peak (HIIT 2.87 ± 1.94 mL·kg¹ ·min^-1 vs standard care 0.15 ± 1.93, with an overall difference of 2.73 mL·kg¹ ·min^-1 95%CI [1.53, 3.93] p<0.001). There were no statistically significant differences between groups for clinical outcomes, although the observed differences consistently favoured the exercise group. This was most notable for total number of complications (0.64 v 1.16 per patient, p=0.07), SF-36 physical component score (p=0.06), and LOS (mean 5.5 v 7.4 days, p=0.07).

CONCLUSIONS

There was a significant improvement in V ˙ O_2peak with a four-week preoperative HIIT program. Further appropriately-powered work is required to explore the impact of preoperative HIIT on postoperative clinical outcomes.

Increased myofilament calcium sensitivity is associated with decreased cardiac troponin I phosphorylation in the diabetic rat heart

NEW FINDINGS

What is the central question of this study? In Zucker Diabetic Fatty rats, does cardiomyocyte myofilament function change through the time course of diabetes and what are the mechanisms behind alterations in calcium sensitivity? What is the main finding and its importance? Zucker Diabetic Fatty rats had increased myofilament calcium sensitivity and reduced phosphorylation at cardiac troponin I without differential O-GlcNAcylation.

ABSTRACT

The diabetic heart has impaired systolic and diastolic function independent of other comorbidities. The availability of calcium is altered, but does not fully explain the cardiac dysfunction seen in the diabetic heart. Thus, we explored if myofilament calcium regulation of contraction is altered while also categorizing the levels of phosphorylation and O-GlcNAcylation in the myofilaments. Calcium sensitivity (pCa₅₀ ) was measured in Zucker Diabetic Fatty (ZDF) rat hearts at the initial stage of diabetes (12 weeks old) and after 8 weeks of uncontrolled hyperglycaemia (20 weeks old) and in non-diabetic (nDM) littermates. Skinned cardiomyocytes were connected to a capacitance-gauge transducer and a torque motor to measure force as a function of pCa (-log[Ca²⁺ ]). Fluorescent gel stain (ProQ Diamond) was used to measure total protein phosphorylation. Specific phospho-sites on cardiac troponin I (cTnI) and total cTnI O-GlcNAcylation were quantified using immunoblot. pCa₅₀ was greater in both 12- and 20-week-old diabetic (DM) rats compared to nDM littermates (P = 0.0001). Total cTnI and cTnI serine 23/24 phosphorylation were lower in DM rats (P = 0.003 and P = 0.01, respectively), but cTnI O-GlcNAc protein expression was not different. pCa₅₀ is greater in DM rats and corresponds with an overall reduction in cTnI phosphorylation. These findings indicate that myofilament calcium sensitivity is increased and cTnI phosphorylation is reduced in ZDF DM rats and suggests an important role for cTnI phosphorylation in the DM heart.

Protein O-GlcNAcylation in the heart

O-GlcNAcylation is a ubiquitous post-translational modification that is extremely labile and plays a significant role in physiology, including the heart. Sustained activation of cardiac O-GlcNAcylation is frequently associated with alterations in cellular metabolism, leading to detrimental effects on cardiovascular function. This is particularly true during conditions such as diabetes, hypertension, cardiac remodelling, heart failure and arrhythmogenesis. Paradoxically, transient elevation of cardiac protein O-GlcNAcylation can also exert beneficial effects in the heart. There is compelling evidence to suggest that a complex interaction between O-GlcNAcylation and phosphorylation also exists in the heart. Beyond direct functional consequences on cardiomyocytes, O-GlcNAcylation also acts indirectly by altering the function of transcription factors that affect downstream signalling. This review focuses on the potential cardioprotective role of protein O-GlcNAcylation during ischaemia-reperfusion injury, the deleterious consequences of chronically elevated O-GlcNAc levels, the interplay between O-GlcNAcylation and phosphorylation in the cardiomyocytes and the effects of O-GlcNAcylation on other major non-myocyte cell types in the heart.

Additional cardiovascular fitness when progressing from moderate- to high-intensity exercise training in previously trained breast cancer survivors

PURPOSE

Cardiovascular disease, often secondary to chemotherapy, is the leading cause of death in BC survivors. Increased aerobic capacity improves post-rehabilitation survival; however, many cancer rehabilitation programs are limited to lower intensity training. High-intensity interval training (HIIT) is associated with the largest improvements in aerobic capacity; therefore, this study aimed to determine whether HIIT would cause a greater increase in VO₂peak than continuous moderate-intensity (MICT) exercise in previously trained BC survivors.

METHODS

Twenty BC survivors who had completed a low/moderate-intensity exercise rehabilitation program performed a VO₂peak test and received a dual-energy X-ray absorptiometry (DXA) scan at baseline and after randomization into a 12-week HIIT or MICT program. ANOVA with repeated measures determined the effects of the different training programs on aerobic capacity and body composition.

RESULTS

Both groups began the training program near or above age- and sex-matched VO₂peak norms. Pre- to post-intervention improvements in VO₂peak (P = 0.006) and waist circumference (P = 0.007) were found in both groups; however, there were no between-group differences. Minute ventilation and peak workload increased in the HIIT group (P < 0.05) but not the MICT group. Body composition was not different after either training program.

CONCLUSIONS

These data suggest that transitioning from low/moderate-intensity exercise to moderate/high-intensity exercise causes further clinically relevant increases in VO₂peak in previously trained BC survivors. HIIT did not cause a significantly greater improvement in VO₂peak than MICT; however, future studies with greater intensity and frequency of training are encouraged.

Exercise in pregnancy: 1-year and 7-year follow-ups of mothers and offspring after a randomized controlled trial

There are limited data on long-term outcomes of mothers or their offspring following exercise interventions during pregnancy. We assessed long-term effects of an exercise intervention (home-based stationary cycling) between 20–36 weeks of gestation on anthropometry and body composition in mothers and offspring after 1 and 7 years. 84 women were randomised to intervention or usual activity, with follow-up data available for 61 mother-child pairs (38 exercisers) at 1 year and 57 (33 exercisers) at 7 years. At 1 year, there were no observed differences in measured outcomes between mothers and offspring in the two groups. At the 7-year follow-up, mothers were mostly similar, except that exercisers had lower systolic blood pressure (−6.2 mmHg; p = 0.049). However, offspring of mothers who exercised during pregnancy had increased total body fat (+3.2%; p = 0.034) and greater abdominal (+4.1% android fat; p = 0.040) and gynoid (+3.5% gynoid fat; p = 0.042) adiposity compared with controls. Exercise interventions beginning during pregnancy may be beneficial to long-term maternal health. However, the initiation of exercise during pregnancy amongst sedentary mothers may be associated with adverse effects in the offspring during childhood. Larger follow-up studies are required to investigate long-term effects of exercise in pregnancy.

Resting heart rate variability and exercise capacity in Type 1 diabetes

People with type 1 diabetes (T1D) have lower exercise capacity (V̇O_2max) than their age‐matched nondiabetic counterparts (CON), which might be related to cardiac autonomic dysfunction. We examined whether Heart Rate Variability (HRV; indicator of cardiac autonomic modulation) was associated with exercise capacity in those with and without T1D. Twenty‐three participants with uncomplicated T1D and 17 matched CON were recruited. Heart rate (HR; ECG), blood pressure (BP; finger photo‐plethysmography), and respiratory rate (respiratory belt) were measured during baseline, paced‐breathing and clinical autonomic reflex tests (CARTs); deep breathing, lying‐to‐stand, and Valsalva maneuver. Baseline and paced‐breathing ECG were analyzed for HRV (frequency‐domain). Exercise capacity was determined during an incremental cycle ergometer test while V̇O₂, 12‐lead ECG, and BP were measured. In uncomplicated T1D, resting HR was elevated and resting HRV metrics were reduced, indicative of altered cardiac parasympathetic modulation; this was generally undetected by the CARTs. However, BP and plasma catecholamines were not different between groups. In T1D, V̇O_2max tended to be lower (P = 0.07) and HR reserve was lower (P < 0.01). Resting Total Power (TP) had stronger positive associations with V̇O_2max (R² ≥ 0.3) than all other traditional indicators such as age, resting HR, and self‐reported exercise (R² = 0.042–0.3) in both T1D and CON. Alterations in cardiac autonomic modulation are an early manifestation of uncomplicated T1D. Total Power was associated with reduced exercise capacity regardless of group, and these associations were generally stronger than traditional indicators.

Impaired ventricular filling limits cardiac reserve during submaximal exercise in people with type 2 diabetes

Background

Attenuated increases in ventricular stroke volume during exercise are common in type 2 diabetes and contribute to reduced aerobic capacity. The purpose of this study was to determine whether impaired ventricular filling or reduced systolic ejection were responsible for the attenuated stroke volume reserve in people with uncomplicated type 2 diabetes.

Methods

Peak aerobic capacity and total blood volume were measured in 17 people with diabetes and 16 non-diabetic controls with no evidence of cardiovascular disease. Left ventricular volumes and other systolic and diastolic functional parameters were measured with echocardiography at rest and during semi-recumbent cycle ergometry at 40 and 60% of maximal aerobic power and compared between groups.

Results

People with diabetes had reduced peak aerobic capacity and heart rate reserve, and worked at lower workloads than non-diabetic controls. Cardiac output, stroke volume and ejection fraction were not different at rest, but increased less in people with diabetes during exercise. Left ventricular end systolic volume was not different between groups in any condition but end diastolic volume, although not different at rest, was smaller in people with diabetes during exercise. Total blood volume was not different between the groups, and was only moderately associated with left ventricular volumes.

Conclusions

People with type 2 diabetes exhibit an attenuated increase in stroke volume during exercise attributed to an inability to maintain/increase left ventricular filling volumes at higher heart rates. This study is the first to determine the role of filling in the blunted cardiac reserve in adults with type 2 diabetes.

Electronic supplementary material

The online version of this article (10.1186/s12933-017-0644-1) contains supplementary material, which is available to authorized users.

Exercise Training Improves but Does Not Normalize Left Ventricular Systolic and Diastolic Function in Adolescents With Type 1 Diabetes

OBJECTIVE

To determine the impact of 20 weeks of exercise training in aerobic capacity on left ventricular function and glycemic control in adolescents with and without type 1 diabetes.

RESEARCH DESIGN AND METHODS

Fifty-three adolescents with type 1 diabetes (aged 15.6 years) were divided into two groups: exercise training (n = 38) and nontraining (n = 15). Twenty-two healthy adolescents without diabetes (aged 16.7 years) were included and, with the 38 participants with type 1 diabetes, participated in a 20-week exercise-training intervention. Assessments included VO_2max and body composition. Left ventricular parameters were obtained at rest and during acute exercise using MRI.

RESULTS

Exercise training improved aerobic capacity (10%) and stroke volume (6%) in both trained groups, but the increase in the group with type 1 diabetes remained lower than trained control subjects. Increased stroke volume in adolescents with type 1 diabetes resulted from greater left ventricular contractility (9% increase in ejection fraction and an 11% reduction in end-systolic volumes) and, to a lesser extent, improved left ventricular filling (6%), suggesting that impaired diastolic function can be affected by exercise training in adolescents with type 1 diabetes. Insulin use decreased by ∼10%, but no change in glycemic status was observed.

CONCLUSIONS

These data demonstrate that in adolescents, the impairment in left ventricular function seen with type 1 diabetes can be improved, although not normalized, with regular intense physical activity. Importantly, diastolic dysfunction, a common mechanism causing heart failure in older subjects with diabetes, appears to be partially reversible in this age group.

'Exercise snacks' before meals: a novel strategy to improve glycaemic control in individuals with insulin resistance

AIMS/HYPOTHESIS

The aim of this study was to investigate whether small doses of intense exercise before each main meal ('exercise snacks') would result in better blood glucose control than a single bout of prolonged, continuous, moderate-intensity exercise in individuals with insulin resistance.

METHODS

Nine individuals completed three exercise interventions in randomised order. Measures were recorded across 3 days with exercise performed on the middle day, as either: (1) traditional continuous exercise (CONT), comprising 30 min moderate-intensity (60% of maximal heart rate [HRmax]) incline walking before dinner; (2) exercise snacking (ES), consisting of 6 × 1 min intense (90% HRmax) incline walking intervals 30 min before each meal; or (3) composite exercise snacking (CES), encompassing 6 × 1 min intervals alternating between walking and resistance-based exercise, 30 min before meals. Meal timing and composition were controlled within participants for exercise interventions.

RESULTS

ES attenuated mean 3 h postprandial glucose concentration following breakfast (by 1.4 ± 1.5 mmol/l, p = 0.02) but not lunch (0.4 ± 1.0 mmol/l, p = 0.22), and was more effective than CONT following dinner (0.7 ± 1.5 mmol/l below CONT; p = 0.04). ES also reduced 24 h mean glucose concentration by 0.7 ± 0.6 mmol/l (p = 0.01) and this reduction persisted for the subsequent 24 h (lower by 0.6 ± 0.4 mmol/l vs CONT, relative to their baselines; p = 0.01). CES was just as effective as ES (p > 0.05 for all glycaemic variables) at improving glycaemic control.

CONCLUSIONS/INTERPRETATION

Dosing exercise as brief, intense 'exercise snacks' before main meals is a time-efficient and effective approach to improve glycaemic control in individuals with insulin resistance.

Prior maximal exercise decreases pulmonary diffusing capacity during subsequent exercise

Pulmonary diffusion (DLCO) increases during exercise due to greater pulmonary capillary volume (Vc) and membrane diffusing capacity (DM). However, after heavy exercise there is a reduction in resting DLCO. It is unclear whether this post-exercise effect will attenuate the normal increase in DLCO, Vc and DM during subsequent exercise and whether this affects SpO2 (pulse oximeter). DLCO, Vc, DM, cardiac output and SpO2 were measured at rest, moderate (~70% VO2peak) and heavy (~90 VO2peak) exercise in 9 subjects during 2 sessions separated by ~90 min. DLCO, Vc and DM increased during exercise (P<0.05). DLCO (P<0.05) and Vc (P<0.10), but not DM or SpO2 were lower in session 2 compared to the first. Reductions in DLCO and Vc appeared to be smallest during rest (1-4%) and greatest at high-intensity exercise (8-20%), but the interaction was not significant. SpO2 decreased by 4.9% and 5.1% from rest to high-intensity exercise during the first and second exercise bout, but these changes were not different. These data confirm that a bout of high-intensity exercise reduces DLCO and Vc, and may indicate that these changes are exacerbated during subsequent high-intensity exercise. Despite these changes, SpO2 was not affected by previous exercise.

Endovascular renal denervation: a novel sympatholytic with relevance to chronic kidney disease

Endovascular renal denervation (sympathectomy) is a novel procedure developed for the treatment of resistant hypertension. Evidence suggests that it reduces both afferent and efferent sympathetic nerve activity, which may offer clinical benefit over and above any blood pressure-lowering effect. Studies have shown objective improvements in left ventricular mass, ventricular function, central arterial stiffness, central haemodynamics, baroreflex sensitivity and arrhythmia frequency. Benefits have also been seen in insulin resistance, microalbuminuria and glomerular filtration rate. In chronic kidney disease, elevated sympathetic activity has been causally linked to disease progression and cardiovascular sequelae. Effecting a marked reduction in sympathetic hyperactivity may herald a significant step in the management of this and other conditions. In this in-depth review, the pathophysiology and clinical significance of the sympatholytic effects of endovascular renal denervation are discussed.

Diastolic function is reduced in adolescents with type 1 diabetes in response to exercise

OBJECTIVE

To determine whether adolescents with type 1 diabetes have left ventricular functional changes at rest and during acute exercise and whether these changes are affected by metabolic control and diabetes duration.

RESEARCH DESIGN AND METHODS

The study evaluated 53 adolescents with type 1 diabetes and 22 control adolescents. Baseline data included peak exercise capacity and body composition by dual-energy X-ray absorptiometry. Left ventricular functional parameters were obtained at rest and during acute exercise using magnetic resonance imaging.

RESULTS

Compared with nondiabetic control subjects, adolescents with type 1 diabetes had lower exercise capacity (44.7 ± 09 vs. 48.5 ± 1.4 mL/kg fat-free mass [FFM]/min; P < 0.05). Stroke volume was reduced in the diabetes group at rest (1.86 ± 0.04 vs. 2.05 ± 0.07 mL/kg FFM; P = 0.02) and during acute exercise (1.89 ± 0.04 vs. 2.17 ± 0.06 mL/kg FFM; P = 0.01). Diabetic adolescents also had reduced end-diastolic volume at rest (2.94 ± 0.06 vs. 3.26 ± 0.09 mL/kg FFM; P = 0.01) and during acute exercise (2.78 ± 0.05 vs. 3.09 ± 0.08 mL/kg FFM; P = 0.01). End-systolic volume was lower in the diabetic group at rest (1.08 ± 0.03 vs. 1.21 ± 0.04 mL/kg FFM; P = 0.01) but not during acute exercise. Exercise capacity and resting and exercise stroke volumes were correlated with glycemic control but not with diabetes duration.

CONCLUSIONS

Adolescents with type 1 diabetes have reduced exercise capacity and display alterations in cardiac function compared with nondiabetic control subjects, associated with reduced stroke volume during exercise.

Design and testing of an MRI-compatible cycle ergometer for non-invasive cardiac assessments during exercise

Background

Magnetic resonance imaging (MRI) is an important tool for cardiac research, and it is frequently used for resting cardiac assessments. However, research into non-pharmacological stress cardiac evaluation is limited.

Methods

We aimed to design a portable and relatively inexpensive MRI cycle ergometer capable of continuously measuring pedalling workload while patients exercise to maintain target heart rates.

Results

We constructed and tested an MRI-compatible cycle ergometer for a 1.5 T MRI scanner. Resting and sub-maximal exercise images (at 110 beats per minute) were successfully obtained in 8 healthy adults.

Conclusions

The MRI-compatible cycle ergometer constructed by our research group enabled cardiac assessments at fixed heart rates, while continuously recording power output by directly measuring pedal force and crank rotation.

Effects of exercise training on maternal hormonal changes in pregnancy

CONTEXT & OBJECTIVE

A recent paper by our group reported that regular aerobic exercise during pregnancy led to lower foetal IGF-I and IGF-II concentrations and a modest reduction in offspring birth weight when compared with the offspring of nontraining control participants. Maternal hormonal alterations in response to exercise training may be associated with the regulation of nutrient availability for foetal growth through placental regulation of maternal metabolism.

OBJECTIVE

To determine whether the reduction in offspring size was associated with changes in the maternal IGF axis [including placental growth hormone (PGH)], leptin and/or free fatty acids (FFA) in response to aerobic exercise training in the second half of pregnancy.

DESIGN AND SETTING

A randomized, controlled trial of exercise in pregnancy.

PATIENTS

Eighty-four healthy nulliparous women (mean±SD age 30±4 year, BMI 25·5±4 kg/m(2) ).

MEASUREMENTS

Serum samples were drawn at 19 and 35 weeks gestation to determine serum IGF-I, IGF-II, IGF-binding protein-1, IGF-binding protein-3, PGH, leptin and FFA.

RESULTS

Exercise training in pregnancy had no impact on the pregnancy-related changes in the maternal IGF axis. Women in the exercise group experienced a 29% increase in leptin in late gestation (P=0·026 vs control) and a trend towards lower FFA (P=0·07 vs control). Late pregnancy changes in maternal leptin were inversely related to offspring birth weight (r= -0·24, P<0·05) and BMI (r= -0·25, P<0·05).

CONCLUSIONS

An increase in leptin in exercising pregnant women may reflect subtle changes within the placenta in response to regular exercise and may contribute to the reduction in offspring size previously reported in this cohort.

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.

Glycemic control influences lung membrane diffusion and oxygen saturation in exercise-trained subjects with type 1 diabetes: alveolar-capillary membrane conductance in type 1 diabetes

Lung diffusing capacity (DLCO) is influenced by alveolar-capillary membrane conductance (D (M)) and pulmonary capillary blood volume (V (C)), both of which can be impaired in sedentary type 1 diabetes mellitus (T1DM) subjects due to hyperglycemia. We sought to determine if T1DM, and glycemic control, affected DLNO, DLCO, D (M), V (C) and SaO(2) during maximal exercise in aerobically fit T1DM subjects. We recruited 12 T1DM subjects and 18 non-diabetic subjects measuring DLNO, DLCO, D (M), and V (C) along with SaO(2) and cardiac output (Q) at peak exercise. The T1DM subjects had significantly lower DLCO/Q and D (M)/Q with no difference in Q, DLNO, DLCO, D (M), or V (C) (DLCO/Q = 2.1 ± 0.4 vs. 1.7 ± 0.3, D (M)/Q = 2.8 ± 0.6 vs. 2.4 ± 0.5, non-diabetic and T1DM, p < 0.05). In addition, when considering all subjects there was a relationship between DLCO/Q and SaO(2) at peak exercise (r = 0.46, p = 0.01). Within the T1DM group, the optimal glycemic control group (HbA1c <7%, n = 6) had higher DLNO, DLCO, and D (M)/Q than the poor glycemic control subjects (HbA1c ≥ 7%, n = 6) at peak exercise (DLCO = 38.3 ± 8.0 vs. 28.5 ± 6.9 ml/min/mmHg, DLNO = 120.3 ± 24.3 vs. 89.1 ± 21.0 ml/min/mmHg, D (M)/Q = 3.8 ± 0.8 vs. 2.7 ± 0.2, optimal vs. poor control, p < 0.05). There was a negative correlation between HbA1c with DLCO, D (M) and D (M)/Q at peak exercise (DLCO: r = -0.70, p = 0.01; D (M): r = -0.70, p = 0.01; D (M)/Q: r = -0.68, p = 0.02). These results demonstrate that there is a reduction in lung diffusing capacity in aerobically fit athletes with T1DM at peak exercise, but suggests that maintaining near-normoglycemia potentially averts lung diffusion impairments.

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.

Exercise training in pregnancy reduces offspring size without changes in maternal insulin sensitivity

CONTEXT

Epidemiological studies have identified the importance of the in utero environment in providing a healthy start to life. Previous studies have suggested that the maternal environment, in particular a reduction in maternal insulin sensitivity, contributes significantly to fetal growth. Regular aerobic exercise, through an effect on maternal insulin sensitivity, may influence offspring size by regulating nutrient supply to the fetus.

OBJECTIVE

The aim of the study was to determine the effects of aerobic exercise training in the second half of pregnancy on maternal insulin sensitivity and neonatal outcomes.

DESIGN AND SETTING

We conducted a community-based, randomized, controlled trial of exercise in pregnancy.

PARTICIPANTS

Eighty-four healthy nulliparous women (mean +/- sd, age, 30 +/- 4 yr; body mass index, 25.5 +/- 4 kg/m(2)) participated in the study.

INTERVENTION

Subjects participated in a home-based stationary cycling program from 20 wk gestation to delivery.

MAIN OUTCOME MEASURES

Maternal insulin sensitivity, neonatal auxology, body composition, and growth-related peptides in cord blood were measured.

RESULTS

Offspring of exercisers had lower birth weight (sd score, control, 0.23 +/- 0.8; exercise, -0.19 +/- 0.9; P = 0.03) and body mass index at birth (sd score, control, 0.40 +/- 0.9; exercise, -0.01 +/- 0.09; P = 0.04). The reduction in maternal insulin sensitivity in late gestation was not affected by exercise (P = 0.45) and was unrelated to offspring size. Exercise offspring had lower cord serum IGF-I (P = 0.03) and IGF-II (P = 0.04).

CONCLUSIONS

Regular exercise was associated with lower birth weights and reduced cord concentrations of growth-related peptides, suggesting an influence of exercise on endocrine regulation of fetal growth. These effects on offspring growth were not associated with an exercise training effect on maternal insulin sensitivity.

Impaired stroke volume and aerobic capacity in female adolescents with type 1 and type 2 diabetes mellitus

AIM/HYPOTHESIS

This study was designed to determine whether type 2 diabetic adolescents have reduced aerobic capacity and to investigate the role of cardiac output and arteriovenous oxygen difference (a-vO(2)) in their exercise response.

METHODS

Female adolescents (age 12-18 years) with type 2 diabetes mellitus (n = 8) and type 1 diabetes mellitus (n = 12) and obese (n = 10) and non-obese (n = 10) non-diabetic controls were recruited for this study. Baseline data included maximal aerobic capacity (cycle ergometer) and body composition. Cardiac output and a-vO(2) were determined at rest and during submaximal exercise.

RESULTS

Diabetic groups had lower aerobic capacity than non-diabetic groups (p < 0.05). Adolescents with type 2 diabetes had lower aerobic capacity than the type 1 diabetic group. Maximal heart rate was lower in the type 2 diabetic group (p < 0.05). Exercise stroke volume was 30-40% lower at 100 and 120 beats per min in the diabetic than in the non-diabetic groups (p < 0.05). The a-vO(2) value was not different in any condition.

CONCLUSIONS AND INTERPRETATION

Type 2 diabetic adolescents have reduced aerobic capacity and reduced heart rate response to maximal exercise. Furthermore, type 2 and type 1 diabetic adolescent girls have a blunted exercise stroke volume response compared with non-diabetic controls. Central rather than peripheral mechanisms contribute to the reduced aerobic capacity in diabetic adolescents. Although of short duration, type 2 diabetes in adolescence is already affecting cardiovascular function in adolescents.

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.

Postural differences in hemodynamics and diastolic function in healthy older men

The shift from upright to supine posture increases stroke volume in healthy young adults, primarily through increased end-diastolic volume. Aging is associated with increased ventricular stiffness and impaired diastolic function. The purpose of this study was to determine whether the stroke volume change between the upright and supine posture was blunted in healthy older men and whether the early mitral inflow response to this postural change was reduced by aging. Pulsed Doppler echocardiography and tissue Doppler imaging were used to assess stroke volume and left ventricular function during upright and supine posture in 10 young and 12 older healthy men. Cardiac output was greater in the supine versus upright condition in both groups. In young men supine posture was associated with a large increment in stroke volume (63.1 +/- 7.2 upright to 98.6 +/- 11.7 ml supine; P < 0.05) and a decrease in heart rate. In older men, the stroke volume increment was smaller (63.9 +/- 3.6 upright to 82.0 +/- 5.7 ml supine; P < 0.05) and heart rate decreased less than young men when comparing upright to supine posture. Increased stroke volume was associated with higher peak early diastolic filling velocity (E) in young men and higher peak late diastolic filling velocity (A) in older men. These findings indicate that healthy aging attenuates the increase in early filling associated with moving from an upright to a supine posture. Furthermore, healthy older men are more dependent upon atrial diastolic filling to augment end-diastolic and stroke volume, which may be due to age-associated increases in left ventricular filling pressure and impaired compliance.

The effect of type 2 diabetes on diastolic function

PURPOSE

This study aimed to determine whether sedentary overweight subjects with type 2 diabetes have impaired diastolic function compared with equally sedentary and overweight nondiabetic subjects.

METHODS

Mitral valve pulsed Doppler echocardiography and tissue Doppler imaging (TDI) were used to assess left ventricular structure and diastolic function in 40- to 60-yr-old sedentary overweight subjects with type 2 diabetes (N = 13) and age- and body mass-matched sedentary nondiabetic subjects (N = 15). Pseudonormal filling was identified using preload reduction and TDI.

RESULTS

Traditional Doppler mitral inflow parameters were not different between groups; however, early diastolic relaxation, as measured by peak early mitral annular velocity (E') and the ratio of E' and peak late mitral annular velocity (E'/A'), was reduced in type 2 diabetic subjects (P < 0.05). The ratio of peak early mitral inflow (E) to E' (E/E'), an estimate of left ventricular filling pressure, was also higher in the type 2 diabetes group (P < 0.05). The proportions of diastolic impairment (69 vs 40%) and pseudonormal filling (39 vs 20%) were not different between groups (P = 0.18).

CONCLUSION

These findings suggest that type 2 diabetes has an effect on diastolic function that is independent of age and body composition.

A randomized controlled graded exercise trial for chronic fatigue syndrome: outcomes and mechanisms of change

The aim of this study was to investigate the potential mechanisms underlying the efficacy of graded exercise therapy for chronic fatigue syndrome (CFS). Forty-nine CFS patients were randomized to a 12-week graded exercise programme or to standard medical care. At the end of treatment the exercise group rated themselves as significantly more improved and less fatigued than the control group. A decrease in symptom focusing rather than an increase in fitness mediated the treatment effect. Graded exercise appears to be an effective treatment for CFS and it operates in part by reducing the degree to which patients focus on their symptoms.

Association of fat-free mass and training status with left ventricular size and mass in endurance-trained athletes

OBJECTIVES

We sought to study the relationship between left ventricular (LV) size and body composition in male endurance athletes and age-matched control subjects.

BACKGROUND

Endurance training is associated with increases in both left ventricular mass (LVM) and left ventricular end-diastolic dimension (LVEDD) in athletes. In other populations, LVM is independently predicted by fat-free mass (FFM). We hypothesized that the increase in LV size and mass observed with training may be a normal response to increased FFM.

METHODS

Twelve young and 18 older male endurance athletes and 10 young and 18 older untrained men underwent exercise testing, echocardiography, and dual-photon x-ray absorptiometry body composition analysis. Univariate correlates (Spearman) and multivariate determinants of LVM and LVEDD were sought from: height, height(1.4), height(2.7), height(3.0), body surface area (BSA), FFM, weight, and body mass index. Un-indexed and indexed LVM and LVEDD were then compared.

RESULTS

Athletes were of a similar age, weight, and height, but had higher FFM and maximum oxygen uptake than untrained men. Both LVM and LVEDD were correlated with body size, including FFM, BSA, weight, and height (all p < 0.05). On multivariate analysis, FFM was the only independent predictor of both LVM (R(2) = 0.36, p < 0.001) and LVEDD (R(2) = 0.35, p < 0.001). Furthermore, LVM and LVEDD (un-indexed and indexed to BSA and height) were different between athletes and non-athletes, but not when indexed to height(2.7) or FFM.

CONCLUSIONS

Both LVM and LVEDD are predicted by FFM in endurance athletes, and when indexed to FFM, no training-related differences were observed. Thus, the extent of LV remodeling (athletic heart) in trained individuals may reflect a normal physiologic response to increased FFM induced by training.

Left ventricular diastolic filling and systolic function of young and older trained and untrained men

Aging is associated with impaired early diastolic filling; however, the effect of endurance training on resting diastolic function in older subjects is unclear. Heart rate and ventricular loading conditions affect mitral inflow velocities measured by Doppler echocardiography; therefore, tissue Doppler imaging of mitral annular velocity, which is relatively preload independent, was combined with mitral inflow velocity and maximal oxygen consumption (V(o2 max)) in young (20-35 yr) and older (60-80 yr) trained and untrained men to determine whether endurance training is associated with an attenuation of age-associated changes in diastolic filling. As expected, V(o2 max) was higher in trained men (P < 0.01) and lower in older men (P < 0.01). Peak early mitral inflow velocity (E) and early-to-late mitral inflow velocity ratios were lower in older vs. young men (P < 0.01); however, there was no training effect (P > 0.05). Peak early mitral annular velocity (E') was higher and peak late mitral annular velocity (A') was lower in young vs. older men (P < 0.01). A significant interaction effect was found for A', E'/A', and peak systolic mitral annular velocity (S'). Training was associated with lower A' in young and higher A' in older men. S' was greater in trained vs. untrained older men (P < 0.05), but it was similar in trained and untrained young men. These findings suggest that early diastolic filling is not affected by training in older men, and the effect of training on A' and S' is different in young and older men.

Resistance training improves glycaemic control in obese type 2 diabetic men

The purpose of this investigation was to determine whether moderate intensity resistance training (RT) improves glycaemic control in obese, type 2 diabetic men. Eighteen subjects were randomly assigned to a 10-week RT program, or a non-training control group (C). Glycosylated haemoglobin (HbA 1c ), fasting glucose and insulin, glucose and insulin 120 minutes (2h) after a 75 g oral glucose load, body composition and muscular strength and endurance were measured before and after the 10-week experimental period. In the RT group fasting glucose and insulin decreased with training (p < 0.05) and decreases in HbA 1c approached significance (p = 0.057). 2-h glucose and insulin did not change in either group. Fat free mass (FFM) increased by 3.5 % after RT but was unchanged in the controls. Fat mass (FM) increased 6.9 % in C but was unchanged in RT. Percent body fat was unchanged in both groups. Muscular strength and endurance increased by 25 to 52 % in the RT group but was unchanged in controls. Changes in fasting glucose and HbA 1c were inversely related to changes in FFM. These results suggest that RT is an effective form of exercise training which modestly improves glycaemic control and lowers fasting insulin levels in obese type 2 diabetics.