Robert Carhart

Effect of 4 weeks of aerobic or resistance exercise training on arterial stiffness, blood flow and blood pressure in pre- and stage-1 hypertensives

The benefits of aerobic exercise (AE) training on blood pressure (BP) and arterial stiffness are well established, but the effects of resistance training are less well delineated. The purpose of this study was to determine the impact of resistance vs aerobic training on haemodynamics and arterial stiffness. Thirty pre- or stage-1 essential hypertensives (20 men and 10 women), not on any medications, were recruited (age: 48.2±1.3 years) and randomly assigned to 4 weeks of either resistance (RE) or AE training. Before and after training, BP, arterial stiffness (pulse wave velocity (PWV)) and vasodilatory capacity (VC) were measured. Resting systolic BP (SBP) decreased following both training modes (SBP: RE, pre 136±2.9 vs post 132±3.4; AE, pre 141±3.8 vs post 136±3.4 mm Hg, P=0.005; diastolic BP: RE, pre 78±1.3 vs post 74±1.6; AE, pre 80±1.6 vs post 77±1.7 mm Hg, P=0.001). Central PWV increased (P=0.0001) following RE (11±0.9–12.7±0.9 m s−1) but decreased after AE (12.1±0.8–11.1±0.8 m s−1). Peripheral PWV also increased (P=0.013) following RE (RE, pre 11.5±0.8 vs post 12.5±0.7 m s−1) and decreased after AE (AE, pre 12.6±0.8 vs post 11.6±0.7 m s−1). The VC area under the curve (VCAUC) increased more with RE than that with AE (RE, pre 76±8.0 vs post 131.1±11.6; AE, pre 82.7±8.0 vs post 110.1±11.6 ml per min per s per 100 ml, P=0.001). Further, peak VC (VCpeak) increased more following resistance training compared to aerobic training (RE, pre 17±1.9 vs post 25.8±2.1; AE, pre 19.2±8.4 vs post 22.9±8.4 ml per min per s per 100 ml, P=0.005). Although both RE and AE training decreased BP, the change in pressure may be due to different mechanisms.

Cardiac autonomic function and baroreflex changes following 4 weeks of resistance versus aerobic training in individuals with pre‐hypertension

Aim:  Cardiac autonomic modulation and baroreflex sensitivity (BRS) are altered in individuals with hypertension. Aerobic exercise (AE) training has been shown to improve both measures, yet little is known about the effects of resistance exercise (RE). The purpose of this study was to examine the heart rate variability (HRV) and BRS following 4 weeks of resistance or aerobic training in a population with borderline high blood pressure (BP).

Resting leptin responses to acute and chronic resistance training in type 2 diabetic men and women

PURPOSE: To evaluate the plasma leptin levels ∼24 h post-exercise in control and type 2 diabetic subjects and to establish if observed changes in leptin concentrations were acute or chronic effects of a resistance training program.METHODS: Thirty men and women (17 controls and 13 type 2, obese diabetics, age 40–55 y) had resting blood samples drawn at 08:00 h (12 h postprandial) at the beginning of the study (pre-training), 24 h after a three repetition maximal weight lifting bout (acute) and 72 h after their last training bout of 6 weeks of resistance training (chronic). The two groups were not matched with respect to body mass index and the control subjects were not normal weight. Subjects weight-trained three times a week, for 6 weeks, for 1 h, training both the upper and lower body.RESULTS: Serum leptin concentrations were significantly higher in the type 2 diabetics than in the control group at pre-training (41.4±8.9 vs 11.4±3.0 ng/ml, P<0.05, respectively). Compared to pre-training, the leptin levels decreased significantly (P<0.01) after acute exercise in the diabetics but not in the control subjects (diabetics 30.9±7.1 vs controls 10.6±2.6 ng/ml). Approximately 72 h after 6 weeks of exercise training, the leptin concentrations were no longer lower than the pre-training values in either group (36.9±8.8 vs 11.9±8.8 ng/ml, respectively, P=NS). When leptin concentrations were log transformed and adjusted for fat mass there were still significant changes in leptin levels over time and between the control and diabetic group (P<0.05).CONCLUSIONS: The type 2 diabetics showed a significant 30% reduction in resting leptin levels 24 h after a single bout of resistance exercise. This was an acute response to resistance exercise and not a chronic training effect (no difference between pre-training and chronic). The decreased resting leptin concentrations ∼24 h post-acute exercise may be due to reduced glucose availability to the adipose tissue, particularly in the diabetic subjects. There is no chronic effect of resistance exercise on leptin concentrations.

Exercise training improves cardiovascular autonomic modulation in response to glucose ingestion in obese adults with and without type 2 diabetes mellitus

This study examined the effect of aerobic exercise training on vagal and sympathetic influences on the modulations of heart rate and systolic blood pressure in response to an oral glucose load in obese individuals with and without type 2 diabetes mellitus (T2D). Beat-to-beat arterial pressure and continuous electrocardiogram were measured after a 12-hour overnight fast and in response to glucose ingestion (75 g dextrose) in obese subjects with (T2D group, n = 23) and without (OB group, n = 36) T2D before and after 16 weeks of aerobic exercise training at moderate intensity. Autonomic modulation was assessed using spectral analysis of systolic blood pressure variability (BPV), heart rate variability (HRV), and analysis of baroreflex sensitivity (BRS). Glucose ingestion significantly increased low-frequency (LF(SBP)), low-frequency HRV (LF(RRI)), and the ratio of low- to high-frequency components of HRV (LF(RRI)/HF(RRI)), and decreased the high-frequency power (HF(RRI)) (P < .05). Exercise training increased LF(RRI) and LF(RRI)/HF(RRI) responses, and reduced HF(RRI) and LF(SBP) to glucose ingestion in both groups (P < .05), but increased fasted BRS in the OB group only (P < .05); glucose intake had no effect on BRS (P > .05). In conclusion, a 16-week exercise training program improved cardiac autonomic modulation in response to an oral glucose load in obese adults, independently of diabetes status, and in the absence of remarkable changes in body weight, body composition, fitness level, and glycemic control.

Plasticity of heart rate signalling and complexity with exercise training in obese individuals with and without type 2 diabetes

Objective:To examine the responsiveness of cardiac autonomic function and baroreflex sensitivity (BRS) to exercise training in obese individuals without (OB) and with type 2 diabetes (ObT2D).Design:Subjects were tested in the supine position and in response to a sympathetic challenge before and after a 16-week aerobic training program. All testing was conducted in the morning following a 12-h fast.Subjects:A total of 34 OB and 22 ObT2D men and women (40–60 years of age) were studied.Measurements:Heart rate variability (HRV) was measured at rest via continuous ECG (spectral analysis with the autoregressive approach) and in response to upright tilt. The dynamics of heart rate complexity were analyzed with sample entropy and Lempel–Ziv entropy, and BRS was determined via the sequence technique. Subjects were aerobically trained 4 times per week for 30–45 min for 16 weeks.Results:Resting HR decreased and total power (lnTP, ms2) of HRV increased in response to exercise training (P<0.05). High frequency power (lnHF) increased in OB subjects but not in OBT2D, and no changes occurred in ln low frequency/HF power with training. Upright tilt decreased lnTP and lnHF and increased LF/HF (P<0.01) but there were no group differences in the magnitude of these changes nor were they altered with training in either group. Tilt also decreased complexity (sample entropy and Lempel–Ziv entropy; P<0.001), but there was no group or training effect on complexity. BRS decreased with upright tilt (P<0.01) but did not change with training. Compared to OB subjects the ObT2D had less tilt-induced changes in BRS.Conclusion:Exercise training improved HRV and parasympathetic modulation (lnHF) in OB subjects but not in ObT2D, indicating plasticity in the autonomic nervous system in response to this weight-neutral exercise program only in the absence of diabetes. HR complexity and BRS were not altered by 16 weeks of training in either OB or ObT2D individuals.

Short-term Training Effects on Diastolic Function in Obese Persons With the Metabolic Syndrome

The aim of this study was to determine the effects of a short‐term high‐intensity exercise program on diastolic function and glucose tolerance in obese individuals with and without metabolic syndrome (MetSyn). Obese men and women (BMI > 30 kg/m2; 39–60 years) with and without the MetSyn (MetSyn 13; non‐MetSyn 18) underwent exercise training consisting of 10 consecutive days of treadmill walking for 1 h/day at 70–75% of peak aerobic capacity. Subjects performed pre‐ and post‐training testing for aerobic capacity, glucose tolerance (2‐h meal test), and standard echocardiography. Aerobic capacity improved for both groups (non‐MetSyn 24.0 ± 1.6 ml/kg/min vs. 25.1 ± 1.5 ml/kg/min; MetSyn 25.2 ± 1.8 ml/kg/min vs. 26.2 ± 1.7 ml/kg/min, P < 0.05). Glucose area under the curve (AUC) improved in the MetSyn group (1,017 ± 58 pmol/l/min vs. 883 ± 75 pmol/l/min, P < 0.05) with no change for the non‐MetSyn group (685 ± 54 pmol/l/min vs. 695 ± 70 pmol/l/min). Isovolumic relaxation time (IVRT) improved in the MetSyn group (97 ± 6 ms vs. 80 ± 5 ms, P < 0.05), and remained normal in the non‐MetSyn group (82 ± 6 ms vs. 86 ± 5 ms). No changes in other diastolic parameters were observed. The overall reduction in IVRT was correlated with a decrease in diastolic blood pressure (DBP) (r = 0.45, P < 0.05), but not with changes in glucose tolerance. Body weight did not change with training in either group. A 10‐day high‐intensity exercise program improved diastolic function and glucose tolerance in the group with MetSyn. The reduction in IVRT in MetSyn was associated with a fall in blood pressure. These data suggest that it may be possible to reverse early parameters of diastolic dysfunction in MetSyn with a high‐intensity exercise program.

Impaired postexercise cardiovascular autonomic modulation in middle-aged women with type 2 diabetes.

Background Type 2 diabetes is associated with cardiovascular autonomic dysfunction. Postexercise autonomic modulation may be different in obese individuals with and without type 2 diabetes. We examined postexercise responses in nondiabetic and diabetic women aged 40–60 years. Methods Hemodynamics, high-frequency and low-frequency of RR interval, low-frequency of systolic blood pressure variability and baroreflex sensitivity were evaluated before and after a 20 min walk at ~65% of VO2 peak in eight lean, 12 obese without type 2 diabetes and eight women with type 2 diabetes. Postexercise measurements were obtained at 10–15, 20–25 and 30–35 min. Results Systolic blood pressure decreased at 10 (P<0.001) and 20 min (P<0.01) in all groups. Total peripheral resistance decreased at 10 min in all women, but the subsequent increase at 20 min was greater (P<0.01) in lean than in diabetic women. Log-transformed low-frequency of systolic blood pressure increased (P<0.01) at 10 and 20 min in all women, but the increase at 10 min was smaller (P<0.05) in diabetic than in lean women. Heart rate was increased (P<0.001) at 10 min in all women and at 20 min in both obese groups. Both log-transformed high-frequency of RR interval and baroreflex sensitivity decreased at 10 and 20 min of recovery in all groups. A group-by-time interaction (P<0.05) was observed for heart rate and baroreflex sensitivity as a lower heart rate and higher baroreflex sensitivity were observed in lean women than in women with type 2 diabetes. Conclusions Reduced postexercise baroreflex sensitivity and responses to autonomic cardiovascular activity contribute to an attenuated recovery of heart rate and total peripheral resistance after brisk walking in middle-aged obese women with type 2 diabetes.

Adrenocortical responses to submaximal exercise in postmenopausal black and white women

The purpose of this study was to determine whether racial differences exist in the dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEAS), and cortisol concentrations of black and white postmenopausal women at rest and in response to submaximal exercise. Twenty-three postmenopausal women (13 white and 10 black) were studied on 2 occasions. On one occasion subjects rested quietly for 4 hours (control day), whereas on the other occasion after 50 minutes of rest, subjects exercised at 70% of Vo(2) peak for 30 minutes on a cycle ergometer (exercise day). Blood was sampled at rest, during exercise, and during recovery and assayed for DHEA, DHEAS, and cortisol concentrations. Resting DHEA and cortisol concentrations and integrated area under the curve (AUC) were similar between the black and white women; however, the black women had lower resting DHEAS concentrations compared with the white women (DHEAS, black: 1.32 +/- 0.29 v white: 2.18 +/- 0.25 micromol. L(-1), P <.05). Regardless of race, DHEA and cortisol AUC increased significantly above resting values (P <.01), but the exercise AUC for DHEA and cortisol were not different between the black and white women (DHEA: 607 +/- 133 and 824 +/- 108 min x nmol. L(-1); cortisol: 9,604 +/- 1,247 and 8,076 +/- 1,093 min x nmol. L(-1), respectively). No exercise-induced change in integrated DHEAS AUC was found in either group. In conclusion, racial differences exist in the resting DHEAS levels of postmenopausal women, but with no racial differences in resting DHEA and cortisol concentrations. Race had no impact on these adrenal hormone responses to submaximal exercise.

Autonomic responses to physiological stressors in women with type 2 diabetes

ObjectiveTo compare autonomic function, measured during handgrip (HG) and cold pressor (CP), between obese with and without type 2 diabetes and non-obese women in fasting and post-glucose load states.MethodsTwelve obese women with type 2 diabetes (50 ± 1 years), 15 obese women without type 2 diabetes (48 ± 2 years), and 12 non-obese women (49 ± 2 years) participated in this study. Heart rate variability (HRV) was determined during autonomic function tests, conducted in both the fasting state and after a glucose challenge (oral glucose tolerance test-OGTT).ResultsObese women with and without diabetes and non-obese women responded similarly fasted and post-glucose challenge, such that in the fasted state low frequency power normalized (LF(nu)) to total power (TP), log transformed (Ln) low frequency to high frequency ratio (LnLF/HF) and heart rate (HR) significantly increased with the autonomic functional tasks (P < 0.05), whereas HF(nu) significantly decreased with the tasks (P < 0.05). Handgrip elicited a lower LnTP and a higher HR (P < 0.05) when compared to CP in the fasted state. In the glucose challenged state LF(nu), LnLF/HF and HR increased (P < 0.05) and HF(nu) significantly decreased (P < 0.05).InterpretationResults of autonomic testing did not differ between obese women, with and without diabetes, and non-obese women. The HG test elicited a greater reduction in HRV total power compared to the CP. This suggests that HG may be more useful when examining autonomic function in women with complicated diabetes.

Endothelial function in patients with newly diagnosed type 2 diabetes receiving early intensive insulin therapy.

BACKGROUND Multifactorial intervention is unable to improve endothelial dysfunction/cardiovascular outcome in type 2 diabetes. Intensive insulin therapy improves pancreatic β-cell dysfunction in patients with early stage diabetes. We investigated the effect of intensive insulin therapy on endothelial dysfunction in these patients. METHODS One hundred and sixteen patients with newly diagnosed type 2 diabetes and 59 healthy subjects received flow-mediated dilatation (FMD) and von Willebrand factor (vWF) measurement. Diabetic patients were further treated with either multifactorial intervention (group A), or intensive insulin therapy (group B) for 2 weeks. Both FMD and vWF measurement were repeated at the same time. FMD was reassessed 90 days after intervention. RESULTS Compared with healthy subjects, FMD in diabetic patients was significantly lower (group A: 15.99 ± 7.81 % vs. 25.17 ± 7.12 %, P < 0.01; group B: 16.85 ± 7.30 % vs. 25.17 ± 7.12%, P < 0.01), plasma vWF was significantly higher (group A: 224.34 ± 7.36 U/l vs. 109.69 ± 6.30 U/l, P < 0.01; group B: 219.18 ± 6.92 U/l vs. 109.69 ± 6.30 U/l, P < 0.01). After treatment, there was no significant change of FMD in either group. The vWF did not change after multifactorial intervention (220.96 ± 6.85 U/l vs. 224.34 ± 7.36 U/l, P = 0.49), but significantly decreased after intensive insulin therapy (155.08 ± 11.82 U/l vs. 219.18 ± 6.92 U/l, P = 0.0013). CONCLUSIONS Intensive insulin therapy significantly improves endothelial injury/dysfunction as measured by vWF in early stage type 2 diabetes. Further study is needed to determine whether plasma vWF can help early identification, stratification and management of diabetic endothelial dysfunction.