Impaired glucose metabolism and the exaggerated blood pressure response to exercise treadmill testing in normotensive patients

The Impact of Insulin Resistance on Cardiovascular Control During Exercise in Diabetes

Patients with diabetes display heightened blood pressure response to exercise, but the underlying mechanism remains to be elucidated. There is no direct evidence that insulin resistance (hyperinsulinemia or hyperglycemia) impacts neural cardiovascular control during exercise. We propose a novel paradigm in which hyperinsulinemia or hyperglycemia significantly influences neural regulatory pathways controlling the circulation during exercise in diabetes.

TRPV1 (Transient Receptor Potential Vanilloid 1) Sensitization of Skeletal Muscle Afferents in Type 2 Diabetic Rats With Hyperglycemia

[Figure: see text].

Exaggerated pressor and sympathetic responses to stimulation of the mesencephalic locomotor region and exercise pressor reflex in type 2 diabetic rats

The cardiovascular responses to exercise are potentiated in patients with type 2 diabetes mellitus (T2DM). However, the underlying mechanisms causing this abnormality remain unknown. Central command (CC) and the exercise pressor reflex (EPR) are known to contribute significantly to cardiovascular control during exercise. Thus these neural signals are viable candidates for the generation of the abnormal circulatory regulation in this disease. We hypothesized that augmentations in CC as well as EPR function contribute to the heightened cardiovascular responses during exercise in T2DM. To test this hypothesis, changes in mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA) in response to electrical stimulation of mesencephalic locomotor region (MLR), a putative component of the central command pathway, and activation of the EPR, evoked by electrically induced hindlimb muscle contraction, were examined in decerebrate animals. Sprague-Dawley rats were given either a normal diet (control) or a high-fat diet (14-16 wk) in combination with two low doses (35 mg/kg week 1, 25 mg/kg week 2) of streptozotocin (T2DM). The changes in MAP and RSNA responses to MLR stimulation were significantly greater in T2DM compared with control (2,739 ± 123 vs. 1,298 ± 371 mmHg/s, 6,326 ± 1,621 vs. 1,390 ± 277%/s, respectively, P < 0.05). Similarly, pressor and sympathetic responses to activation of the EPR in diabetic animals were significantly augmented compared with control animals (436 ± 74 vs. 134 ± 44 mmHg/s, 645 ± 135 vs. 139 ± 65%/s, respectively, P < 0.05). These findings provide the first evidence that CC and the EPR may generate the exaggerated rise in sympathetic activity and blood pressure during exercise in T2DM.

Hypertensive response to exercise: mechanisms and clinical implication

A hypertensive response to exercise (HRE) is frequently observed in individuals without hypertension or other cardiovascular disease. However, mechanisms and clinical implication of HRE is not fully elucidated. Endothelial dysfunction and increased stiffness of large artery contribute to development of HRE. From neurohormonal aspects, excess stimulation of sympathetic nervous system and augmented rise of angiotensin II seems to be important mechanism in HRE. Increasing evidences indicates that a HRE is associated with functional and structural abnormalities of left ventricle, especially when accompanied by increased central blood pressure. A HRE harbors prognostic significance in future development of hypertension and increased cardiovascular events, particularly if a HRE is documented in moderate intensity of exercise. As supported by previous studies, a HRE is not a benign phenomenon, however, currently, whether to treat a HRE is controversial with uncertain treatment strategy. Considering underlying mechanisms, angiotensin receptor blockers and beta blockers can be suggested in individuals with HRE, however, evidences for efficacy and outcomes of treatment of HRE in individuals without hypertension is scarce and therefore warrants further studies.

Exaggerated Exercise Blood Pressure Response and Future Cardiovascular Disease

Exaggerated blood pressure (BP) response to exercise predicts future hypertension. However, there is considerable lack of understanding regarding the mechanism of how this abnormal response is generated, and how it relates to the future establishment of cardiovascular disease. The authors studied 82 healthy male volunteers without cardiovascular risk factors. The participants were categorized into two age-matched groups depending on their exercise systolic BP (ExSBP) rise after 3 minutes of exercise using a submaximal step test: exaggerated ExSBP group (hyper-responders [peak SBP ≥ 180 mm Hg]) and low ExSBP responder group (hypo-responders [peak SBP <180 mm Hg]). Forearm venous occlusion plethysmography and intra-arterial infusions of acetylcholine (ACh), N(G)-monomethyl-L-arginine (L-NMMA), sodium nitroprusside (SNP), and norepinephrine (NE) were used to assess vascular reactivity. Proximal aortic compliance was assessed with ultrasound, and neurohormonal blood sampling was performed at rest and during peak exercise. The hyper-responder group exhibited a significantly lower increase in forearm blood flow (FBF) with ACh compared with the hypo-responder group (ΔFBF 215% [14] vs 332.3% [28], mean [standard error of the mean]; P<.001), as well as decreased proximal aortic compliance. The vasoconstrictive response to L-NMMA was significantly impaired in the hyper-responder group in comparison to the hypo-responder group (ΔFBF -40.2% [1.6] vs -50.2% [2.6]; P<.05). In contrast, the vascular response to SNP and NE were comparable in both groups. Peak exercise plasma angiotensin II levels were significantly higher in the hyper-responder group (31 [1] vs 23 [2] pg/mL, P=.01). An exaggerated BP response to exercise is related to endothelial dysfunction, decreased proximal aortic compliance, and increased exercise-related neurohormonal activation, the constellation of which may explain future cardiovascular disease.

Increased mean arterial pressure response to dynamic exercise in normotensive subjects with multiple metabolic risk factors

Metabolic syndrome (MS) may influence vascular reactivity and might cause an excessive increase in blood pressure (BP) during dynamic exercise. We examined this hypothesis in 698 normotensive men (mean age: 43 years) free of cardiovascular disease, diabetes mellitus and renal disease. The response of BP to exercise was assessed by the mean arterial pressure (MAP) during bicycle ergometry. The MAP values were expressed as z-scores normalized to the relative increases in heart rate. High-normal BP, dyslipidemia and hyperglycemia were diagnosed according to the Japan-specific MS criteria. The z-score of MAP was significantly higher in subjects with high-normal BP (+0.57, P<0.001), dyslipidemia (+0.18, P<0.001) and hyperglycemia (+0.24, P<0.001) than in those without MS component (-0.38). In the high-normal BP subjects, the addition of dyslipidemia and/or hyperglycemia was associated with a progressive increase in the z-score of exercise MAP, whereas no such association was observed in the normal-BP subjects (P=0.033, two-way ANOVA). Multivariate regression analysis revealed that a greater number of MS components (β=0.102, P=0.010) was an independent determinant of increased MAP z-score after adjustment for potential confounders, including age (β=0.123, P<0.001), body mass index (β=0.145, P<0.001) and high-normal BP (β=0.410, P<0.001). These results suggest that accumulation of MS components may alter vascular structure and function and lead to the significant elevation of MAP during dynamic exercise even before clinical manifestation of arterial hypertension.

Metabolic syndrome and exaggerated blood pressure response to exercise in newly diagnosed hypertensive patients

Background: Running evidence supports a prognostic value of an exaggerated blood pressure response to exercise (EBPR). The impact of the metabolic syndrome (MS) on EBPR in hypertensive patients has not been investigated.

Design: A cross-sectional study in the setting of an outpatient hypertension clinic.

Methods: In total, 325 non-diabetic patients with newly diagnosed hypertension were divided into two groups based on the presence ( n = 95) or absence ( n = 230) of the MS as defined with NCEP-ATP III criteria. All subjects underwent ambulatory blood pressure monitoring, echocardiography and exercise treadmill testing.

Results: Hypertensive patients with MS exhibited higher prevalence of EBPR (by 17%, p = 0.002) and peak exercise systolic BP (by 10.4 mmHg, p = 0.001) irrespectively of confounders. Metabolic equivalents were higher in hypertensives with MS (by 0.6 ml/kg/min, p = 0.048), but the difference lost significance after adjusting for confounders, including body mass index. Logistic regression analysis identified the MS as an independent predictor of an EBPR ( p = 0.016). Hypertensive patients with MS had a 2.3-fold risk of exhibiting EBPR compared to those without MS. However, individual components of MS altogether as well as each one separately failed to predict EBPR.

Conclusions: Presence of MS in newly diagnosed hypertensive patients is associated with increased peak exercise BP and a higher frequency of EBPR over and above its separate elements.

Cardiovascular disease risk factors and blood pressure response during exercise in healthy children and adolescents: the European Youth Heart Study

Raised blood pressure (BP) response during exercise independently predicts future hypertension. Subjects with higher BP in childhood also have elevated BP later in life. Therefore, the factors related to the regulation of exercise BP in children needs to be well understood. We hypothesized that physiological cardiovascular disease (CVD) risk factors would influence BP response during exercise in children and adolescents. This is a cross-sectional study of 439 Danish third-grade children and 364 ninth-grade adolescents. Systolic blood pressure (SBP) was measured with sphygmomanometer during a maximal aerobic fitness test. Examined CVD risk factors were high-density lipoprotein (HDL)- and low-density lipoprotein (LDL)-cholesterol, triglyceride, homeostasis model of assessment of insulin resistance (HOMA-IR) score, body mass index (BMI), waist circumference, and aerobic fitness. A random effect model was used to test the hypotheses. In boys, HOMA-IR score and BMI were positively related to SBP response during exercise (β = 1.03, P = 0.001, and β = 0.58, P = 0.017, respectively). The effects sizes of HOMA-IR score and BMI and the significance levels only changed slightly (β = 0.91, P = 0.004, and β = 0.43, P = 0.08, respectively) when the two variables were added in the same model. A significant positive association was observed between aerobic fitness and SBP response in girls (β = 3.13 and P = 0.002). HOMA-IR score and BMI were found to be positively related to the SBP response in male children and youth. At least partly, adiposity and insulin sensitivity seem to influence exercise SBP through different mechanisms. The positive relationship observed between aerobic fitness and SBP response in girls remains unexplainable for us, although post hoc analyses revealed that it was the case in the ninth graders only.