The acute effect of hyperglycaemia on vessel wall properties

Acute Central Hemodynamic Effects of a Volume Exchange in Peritoneal Dialysis

Background

Although peritoneal dialysis is considered to offer more hemodynamic stability than hemodialysis, the acute hemodynamic effects of peritoneal dialysis have only been investigated scarcely. The present study assesses the central hemodynamic impact of volume infusion using pH-adjusted icodextrin, thus avoiding interference of glucose, pH, and osmolarity.

Methods

Patients were randomized to 3 different starting volumes (A: 1000 mL, B: 1500 mL, and C: 2500 mL) of icodextrin, followed by addition (A and B) or drainage (C) of 200 mL every 10 minutes for 50 minutes. Local carotid systolic blood pressure (BP; as a surrogate for central BP), augmentation index, and augmentation pressure were measured by applanation tonometry before and after infusion of the starting volumes and after each volume change.

Results

We included 13 patients (median age 57 years). Baseline brachial BP was 126/77 mmHg. After infusion of the starting volume, carotid systolic BP and augmentation pressure increased by 4.7 mmHg ( p = 0.006) and 3.1 mmHg ( p = 0.015). Augmentation index increased by 5.7% ( p = 0.04) and heart rate decreased by 2.6/minute ( p = 0.006). Intraperitoneal pressure increased by 2.3 cm H2O ( p = 0.03). No additional hemodynamic changes except for a rise in diastolic BP with increasing volume ( p = 0.004) were observed after subsequent addition or removal of volumes.

Conclusions

Infusion of peritoneal dialysis fluids causes an acute increase in carotid systolic B P, followed by a progressive rise in diastolic BP. These effects persist until complete drainage of the abdomen and may be due to an enhanced preload, resulting from intraperitoneal venous compression, and/or increased wave reflection.

Insulin exposure mitigates the increase of arterial stiffness in patients with type 2 diabetes and albuminuria: an exploratory analysis

AIMS

Insulin possesses both vasodilatory and sympathomimetic activities. The aim was to examine the relationship between changes in insulin exposure and arterial stiffness in type 2 diabetes (T2D).

METHODS

Patients with T2D with (n = 22) or without (n = 24) albuminuria, and non-diabetic controls (n = 25) were randomized to a crossover study having a breakfast with or without pre-meal rapid-acting insulin. Pulse wave velocity (PWV) was measured at 30 min before and at 60-min intervals up to 240 min after the breakfast.

RESULTS

At baseline, both postprandial aortic (p = 0.022) and brachial (p = 0.011) PWV were higher in individuals with T2D than in healthy controls irrespective of the presence of albuminuria. In patients with albuminuria, weight-adjusted insulin dose correlated inversely with the excursion of the aortic (r = - 0.412, p = 0.006) and brachial (r = - 0.372; p = 0.014) PWV. Similarly, circulating endogenous insulin concentrations correlated inversely with the aortic (r = - 0.347, p = 0.026) and brachial (r = - 0.622, p = <0.001) PWV. No correlations between insulin and PWV were observed in patients without albuminuria or in healthy controls.

CONCLUSIONS

The inverse correlation between insulin and PWV in T2D with albuminuria may reflect a vasorelaxing effect of insulin.

CLINICAL TRIAL REGISTRATION NUMBER

The study was registered (clinicaltrials.gov) with the identifier of NCT01159938.

Short-term effects of a standardized glucose load on region-specific aortic pulse wave velocity assessed by MRI

PURPOSE

To assess the short-term effects of a standardized oral glucose load on regional aortic pulse wave velocity (PWV) using two-directional in-plane velocity encoded MRI.

MATERIALS AND METHODS

A randomized, controlled intervention was performed in 16 male subjects (mean ± standard deviation: age: 59±7 years, body mass index: 28±3 kg/m2) with impaired fasting glucose. The intervention consisted of an oral glucose load (75 grams of carbohydrates in 300 mL water) at 1 study day and water (300 mL) at the other study day. PWV was measured using multislice two-directional in-plane velocity-encoded MRI.

RESULTS

PWV in the proximal aorta at 1 h post-glucose load decreased compared with PWV 1-h post-water (delta PWV: -1.0±2.6 m/s versus 0.6±2.0 m/s, P=0.02). Eight responding subjects showed a significant decrease in PWV of the proximal aorta after the glucose load and had a decreased waist circumference (P=0.037) compared with nonresponders, being one of the major criteria of the metabolic syndrome. There was no significant change in PWV of the distal aorta at 1 h post-load comparing both intervention groups.

CONCLUSION

A standardized oral glucose load induces a decrease of the proximal, but not of the distal, aortic PWV. Regional response of aortic PWV may be associated with features of the metabolic syndrome.

Relationship Between Glycosylated Hemoglobin and Arterial Elasticity

Arterial elasticity is decreased in diabetes, but it is unclear whether there is a relationship between glycosylated hemoglobin (HbA1c) and arterial elasticity. To evaluate this question, 111 subjects with diabetes mellitus had HbA1c and arterial elasticity determined in an academic outpatient setting. Three measurements of arterial elasticity indices were obtained supine using the HDI/PulseWave CR-2000 Research CardioVascular Profiling System (Hypertension Diagnostics Inc., Eagan, MN). The study population was 49% black and 51% women. Population characteristics included age, 49.2 years; duration of diabetes, 12.1 years; HbA1c, 8.9%; large artery elasticity, 11.8 mL/mm Hg x 10; and small artery elasticity, 4.7 mL/mm Hg x 100. Age correlated with diminished large artery elasticity. Women had a lower large artery elasticity than men (10.6 vs. 13.3 mL/mm Hg x 10; p = 0.0002). Decreasing small artery elasticity was associated with increasing age (p = 0.0001), HbA1c (p = 0.0184), and African-American ethnicity (p = 0.0306). Women had less small artery elasticity than men (3.8 vs. 5.8 mL/mm Hg x 100; p = 0.0001). Black diabetic patients had a reduced arterial elasticity compared with whites. Increasing HbA1c is associated with decreasing small artery elasticity, but not large artery elasticity. In diabetic patients, small artery elasticity is reduced to a greater extent in women than men and in blacks than whites.

Cardiac and vascular function in adolescents and young adults with type 1 diabetes

The objective was to prospectively define cardiac and vascular function in adolescents and young adults with type 1 diabetes over a 3-year period. Thirty-three subjects with type 1 diabetes were studied in 1998, and 28 returned for follow-up in 2001. There were 28 controls without diabetes. All subjects underwent ultrasonography of the carotid artery to determine distensibility, compliance, and intimal-medial thickness, as well as echocardiographic studies, lipid profile, and measurement of hemoglobin A1c (HbA1c) levels and urinary albumin excretion rate. The diabetes group showed no significant change over the 3-year follow-up in lipid profile, HbA1c level, or albumin excretion rate, but a significant increase in body mass index. The diabetes and control groups were similar in age, lipid profile, and albumin excretion rate. Carotid artery distensibility and compliance in the diabetes group increased significantly from baseline to follow-up but did not differ significantly from controls. The intimal-medial thickness of the diabetes group remained unchanged over time but tended to be higher than controls. Echocardiographic studies showed no difference between the diabetes and control groups, but there was a small change in left ventricular posterior diastolic wall diameter in the subjects with diabetes over the 3-year period. There was an overall improvement in carotid function and no change in cardiac measures in subjects with diabetes over the 3 years, such that cardiac and vascular function were similar to those of controls. The reason for the improvement is uncertain, but may relate to the improvement of insulin sensitivity at the end of the pubertal growth period, rather than to changes in metabolic control or lipid profiles.

Stent implantation alters coronary artery hemodynamics and wall shear stress during maximal vasodilation

Coronary stents improve resting blood flow and flow reserve in the presence of stenoses, but the impact of these devices on fluid dynamics during profound vasodilation is largely unknown. We tested the hypothesis that stent implantation affects adenosine-induced alterations in coronary hemodynamics and wall shear stress in anesthetized dogs (n = 6) instrumented for measurement of left anterior descending coronary artery (LAD) blood flow, velocity, diameter, and radius of curvature. Indexes of fluid dynamics and shear stress were determined before and after placement of a slotted-tube stent in the absence and presence of an adenosine infusion (1.0 mg/min). Adenosine increased blood flow, Reynolds (Re) and Dean numbers (De), and regional and oscillatory shear stress concomitant with reductions in LAD vascular resistance and segmental compliance before stent implantation. Increases in LAD blood flow, Re, De, and indexes of shear stress were observed after stent deployment (P < 0.05). Stent implantation reduced LAD segmental compliance to zero and potentiated increases in segmental and coronary vascular resistance during adenosine. Adenosine-induced increases in coronary blood flow and reserve, Re, De, and regional and oscillatory shear stress were attenuated after the stent was implanted. The results indicate that stent implantation blunts alterations in fluid dynamics during coronary vasodilation in vivo.

Arterial elastic properties and cardiovascular risk/event

Cardiovascular disease is a major cause of morbidity and mortality in the western world. There is convincing evidence that the elastic properties, particularly of large arteries, are impaired in the presence of cardiovascular disease and risk factors such as cigarette smoking, hypertension, diabetes and ageing. Evidence is also emerging that treatment of these risk factors is associated with an improvement in the elastic properties, mirrored by a reduction in the cardiovascular risk and events. The main problems associated with arterial elasticity are the multiple definitions and methods of measurement and the problem of obtaining reliable nearby blood pressure measurement. Nevertheless, duplex estimation appears to be a non-invasive, accurate and reliable method of defining these properties. This method is broadly used as a research tool, but there is a good case for its use in clinical practice, particularly in the screening of patients at risk of cardiovascular events.

Change in common carotid artery diameter, distensibility and compliance in subjects with a recent history of impaired glucose tolerance: a 3-year follow-up study

OBJECTIVE

To assess the development of common carotid artery properties (diameter, distensibility and compliance) in a cohort of 140 subjects (mean age 65.8 years, SD 7.5 years) originally diagnosed as impaired glucose tolerant in a population-based study, and to explore determinants of changes observed.

DESIGN

An observational, longitudinal study over a 3-year-period.

METHODS

Vessel wall movement detector system based on ultrasonography, linear generalized estimating equations.

RESULTS

Carotid artery diameter rose from 6.87-7.02 mm (+ 2.2%, P<0.001). Distensibility decreased from 11.8 to 10.9 x 10-3 kPa-1 (-8.3%, P=0.009). Compliance decreased from 0.44-043 mm2 kPa-1 (P=0.17). Changes in blood pressure level were negatively associated with changes in distensibility and compliance. Baseline fasting glucose levels were positively associated with changes in diameter, while fasting insulin levels were negatively associated with changes in distensibility and compliance in men, but not in women.

CONCLUSIONS

In subjects with a recent history of impaired glucose tolerance, we observed an increase in carotid artery diameter and a decrease in distensibility. Change in blood pressure level and baseline fasting glucose and HbA1c levels were positively related to the increase in diameter. In men, but not in women, baseline fasting insulin levels were associated with an acceleration of these changes.

Diminished wave reflection in the aorta. A novel physiological action of insulin on large blood vessels

Epidemiological data suggest that insulin may have direct effects on large-vessel function, but thus far insulin has only been shown, after prolonged infusions, to slowly decrease peripheral vascular resistance by increasing muscle blood flow. We determined whether physiological doses of insulin affect function of large arteries, before any changes in peripheral blood flow, in vivo using pulse wave analysis. Nine normal men were studied on 2 occasions: once during a 6-hour infusion of saline and once under normoglycemic hyperinsulinemic conditions (sequential 2-hour insulin infusions of 1, 2, and 5 mU/kg. min). Central aortic pressure waves were synthesized from those recorded in the periphery with the use of applanation tonometry and a validated reverse transfer function every 30 minutes. This allowed determination of central aortic augmentation (the pressure difference between early and late systolic pressure peaks) and augmentation index (augmentation expressed as a percentage of pulse pressure). Both augmentation and augmentation index decreased significantly within 1 hour after administration of insulin (P<0.001) but not saline. Systolic and diastolic blood pressure and heart rate remained unchanged for the first 2 hours. A significant increase in peripheral (forearm) blood flow was not observed until 2.5 hours after start of the insulin infusion. These data demonstrate that insulin, in normal subjects, rapidly decreases wave reflection in the aorta. This beneficial effect is consistent with increased distensibility or vasodilatation of large arteries. In contrast to the effect of insulin on peripheral blood flow, this action of insulin is observed under conditions in which both the insulin dose and duration of insulin exposure are physiological. Resistance to this action of insulin could provide a mechanism linking insulin resistance and conditions such as hypertension at the level of large arteries.