Ruth M. Franklin

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.

Intramyocellular Lipids: Effect of Age, Obesity, and Exercise

Abstract Obese individuals with metabolic syndrome are predicted to have a 5 times greater risk of developing type 2 diabetes and a 3 times greater risk of myocardial infarction than those without metabolic syndrome. Many obese patients with metabolic risk factors have an accumulation of triglycerides within the skeletal muscle fibers, ie, intramyocellular lipids (IMCL). Individuals with metabolic syndrome have a greater risk of developing IMCL depots, and these stores are related to increased cardiovascular risk and type 2 diabetes. A few studies have shown, moreover, that aging seems to result in an increase in IMCL stores, although little is known about how exercise influences these stores. In healthy young individuals, IMCL depots have been shown to decrease in response to acute exercise, but very little is known about the effects of exercise training on IMCL depots in obese individuals. Understanding how IMCL depots can be altered with exercise (both resistance and aerobic exercise) in older and obese individuals seems to be critical in preventing disease.

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.