John O. Prior

Coronary Circulatory Dysfunction in Insulin Resistance, Impaired Glucose Tolerance, and Type 2 Diabetes Mellitus

Background—Abnormal coronary endothelial reactivity has been demonstrated in diabetes and is associated with an increased rate of cardiovascular events. Our objectives were to investigate the presence of functional coronary circulatory abnormalities over the full spectrum of insulin resistance and to determine whether these would differ in severity with more advanced states of insulin resistance. Methods and Results—Myocardial blood flow (MBF) was measured with positron emission tomography and 13N-ammonia to characterize coronary circulatory function in states of insulin resistance without carbohydrate intolerance (IR), impaired glucose tolerance (IGT), and normotensive and hypertensive type 2 diabetes mellitus (DM) compared with insulin-sensitive (IS) individuals. Indices of coronary function were total vasodilator capacity (mostly vascular smooth muscle–mediated) during pharmacological vasodilation and the nitric oxide–mediated, endothelium-dependent vasomotion in response to cold pressor testing. Total vasodilator capacity was similar in normoglycemic individuals (IS, IR, and IGT), whereas it was significantly decreased in normotensive (−17%) and hypertensive (−34%) DM patients. Compared with IS, endothelium-dependent coronary vasomotion was significantly diminished in IR (−56%), as well as in IGT and normotensive and hypertensive diabetic patients (−85%, −91%, and −120%, respectively). Conclusions—Progressively worsening functional coronary circulatory abnormalities of nitric oxide–mediated, endothelium-dependent vasomotion occur with increasing severity of insulin-resistance and carbohydrate intolerance. Attenuated total vasodilator capacity accompanies the more clinically evident metabolic abnormalities in diabetes.

Chronic inflammation and impaired coronary vasoreactivity in patients with coronary risk factors.

Background—The goal of this study was to examine a possible association between systemic microinflammation, as reflected by C-reactive protein (CRP) serum levels, and coronary vasomotion in patients with coronary risk factors but with angiographically normal coronary arteries. Methods and Results—Coronary vasomotor function was studied in response to cold pressor testing (CPT) in 71 patients with normal angiograms. In all patients, CPT-induced changes in epicardial luminal area (LA; mm2) were assessed with quantitative angiography. Within 20 days, myocardial blood flow (MBF) responses to CPT were measured (mL · g−1 · min−1) noninvasively with 13N-ammonia and PET imaging. The CPT-induced mean changes in LA and in MBF in patients with elevated CRP (≥0.5 mg/dL) were significantly impaired compared with patients presenting with CRP levels within normal range (<0.5 mg/dL) (&Dgr;LA, −1.09±0.86 versus 0.45±0.63 mm2; &Dgr;MBF, 0.06±0.18 versus 0.44±0.31 mL · g−1 · min−1; P<0.0001, respectively). Coronary LA changes and MBF responses to CPT were inversely correlated with CRP serum levels (r=−0.84 and r=−0.63; P<0.0001). Lastly, regression analysis revealed a significant correlation between the changes in LA and MBF during CPT for patients with elevated CRP levels and those for patients with normal CRP levels (r=0.56 and r=0.66; P<0.001). Conclusions—These findings suggest a direct association between systemic microinflammation and altered coronary vasomotor function of both the epicardial conductance and the arteriolar resistance vessels.

Determinants of myocardial blood flow response to cold pressor testing and pharmacologic vasodilation in healthy humans

PurposeResponse of myocardial blood flow (MBF) to sympathetic stimulation with cold is modulated by endothelium-related factors and is typically altered in the presence of coronary risk factors. Determinants of flow response to cold pressor testing (CPT) in normal volunteers at low risk for CAD remain less well defined, especially relative to baseline conditions such as hemodynamics and MBF, plasma substrate and lipid levels, and total pharmacologically stimulated vasodilator capacity.MethodsIn 50 normal volunteers (42±13xa0years; 31 women) without coronary risk factors, insulin resistance, or family history of diabetes/premature CAD, MBF was measured with 13N-ammonia and PET at baseline, during CPT, and during pharmacologic hyperemia.ResultsSympathetic stimulation with CPT raised heart rate and blood pressure and thus MBF (ΔMBF=0.23±0.09xa0ml/min/g). MBF response, defined in absolute flow units as the difference between CPT and baseline, was independent of age, gender, heart rate, and blood pressure and rate–pressure product (RPP) at baseline as well as plasma substrate and lipid levels with the exception of an association with HDL cholesterol (ρ=0.40, p=0.005) but depended on the change in RPP from rest (ρ=0.33, p=0.019). Finally, changes in coronary vascular resistance in response to CPT were associated with changes in pharmacologic vasodilation (ρ=0.56, p<0.0001).ConclusionMBF response to sympathetic stimulation with cold (NO-mediated endothelium-dependent vasomotion), reflecting the functional state of the coronary endothelium, was independent of gender, age, and resting heart conditions. It was modulated by HDL cholesterol levels, even in healthy volunteers, and also related to pharmacologically stimulated vasodilator capacity at the coronary vascular resistance level.

Assessment of intra- and interobserver reproducibility of rest and cold pressor test-stimulated myocardial blood flow with 13N-ammonia and PET

PurposeWe investigated the intraobserver reproducibility of myocardial blood flow (MBF) measurements with PET at rest and during cold pressor test (CPT), and the interobserver agreement.MethodsTwenty normal volunteers were studied. Using 13N-ammonia, MBF was measured at rest and during CPT and measurement was repeated in a 1-day session (short-term reproducibility; SR). After a follow-up of 2xa0weeks, MBF was measured again at rest and during CPT and compared with the initial baseline measurement (long-term reproducibility; LR). In addition, adenosine-induced hyperemic MBF increases were assessed.ResultsAssessment of the SR did not show a significant absolute difference in MBF at rest, MBF during CPT or the endothelium-related change in MBF from rest to CPT (ΔMBF) (0.09u2009±u20090.10, 0.11u2009±u20090.09, and 0.08u2009±u20090.05xa0ml/g/min; pu2009=u2009NS), and they were linearly correlated (ru2009=u20090.72, ru2009=u20090.76 and ru2009=u20090.84; pu2009<u20090.0001). Corresponding values for standard error of the estimate (SEE), as indicative for the range of MBF measurement error, were 0.14, 0.14, and 0.09xa0ml/g/min. The LR yielded relatively higher but non-significant absolute differences in the MBF at rest, MBF during CPT and ΔMBF (0.10u2009±u20090.10, 0.14u2009±u20090.10, and 0.19u2009±u20090.10xa0ml/g/min; pu2009=u2009NS), and paired MBFs significantly correlated (ru2009=u20090.75, ru2009=u20090.71, and ru2009=u20090.60; pu2009<u20090.001). Corresponding SEEs were 0.13, 0.15, and 0.16xa0ml/g/min. The interobserver analysis yielded a high correlation for MBF at rest, MBF during CPT, and hyperemic MBF (ru2009=u20090.96, SEE=0.04; ru2009=u20090.78, SEE=0.11; and ru2009=u20090.87, SEE=0.28; pu2009<u20090.0001, respectively), and also a good interobserver correlation for ΔMBF (ru2009=u20090.62, SEE=0.09; pu2009<u20090.003).ConclusionShort- and long-term MBF responses to CPT, as an index for endothelium-related coronary vasomotion, can be measured reproducibly with 13N-ammonia PET. In addition, the high interobserver reproducibility for repeat analysis of MBF values suggests the measurements to be largely operator independent.

Structural alterations of the coronary arterial wall are associated with myocardial flow heterogeneity in type 2 diabetes mellitus

PurposeTo determine the relationship between carotid intima–media thickness (IMT), coronary artery calcification (CAC), and myocardial blood flow (MBF) at rest and during vasomotor stress in type 2 diabetes mellitus (DM).MethodsIn 68 individuals, carotid IMT was measured using high-resolution vascular ultrasound, while the presence of CAC was determined with electron beam tomography (EBT). Global and regional MBF was determined in milliliters per gram per minute with 13N-ammonia and positron emission tomography (PET) at rest, during cold pressor testing (CPT), and during adenosine (ADO) stimulation.ResultsThere was neither a relationship between carotid IMT and CAC (ru2009=u20090.10, pu2009=u20090.32) nor between carotid IMT and coronary circulatory function in response to CPT and during ADO (ru2009=u2009−0.18, pu2009=u20090.25 and ru2009=u20090.10, pu2009=u20090.54, respectively). In 33 individuals, EBT detected CAC with a mean Agatston-derived calcium score of 44u2009±u200918. There was a significant difference in regional MBFs between territories with and without CAC at rest and during ADO-stimulated hyperemia (0.69u2009±u20090.24 vs. 0.74u2009±u20090.23 and 1.82u2009±u20090.50 vs. 1.95u2009±u20090.51xa0ml/g/min; pu2009≤u20090.05, respectively) and also during CPT in DM but less pronounced (0.81u2009±u20090.24 vs. 0.83u2009±u20090.23xa0ml/g/min; pu2009=u2009ns). The increase in CAC was paralleled with a progressive regional decrease in resting as well as in CPT- and ADO-related MBFs (ru2009=u2009−0.36, pu2009≤u20090.014; ru2009=u2009−0.46, pu2009≤u20090.007; and ru2009=u2009−0.33, pu2009≤u20090.041, respectively).ConclusionsThe absence of any correlation between carotid IMT and coronary circulatory function in type 2 DM suggests different features and stages of early atherosclerosis in the peripheral and coronary circulation. PET-measured MBF heterogeneity at rest and during vasomotor stress may reflect downstream fluid dynamic effects of coronary artery disease (CAD)-related early structural alterations of the arterial wall.

Improvement in coronary vascular dysfunction produced with euglycaemic control in patients with type 2 diabetes

Objective: To determine the effect of plasma glucose lowering on coronary circulatory function in type 2 diabetes mellitus. Methods: Twenty patients with type 2 diabetes and 18 weight-matched controls were studied. At baseline, myocardial blood flow (MBF) was measured with [13N]ammonia and positron emission tomography at rest, during cold pressor testing (CPT), and during adenosine hyperaemia. In diabetic patients, MBF and blood chemistry were analysed again after 3 months of glucose-lowering treatment with glyburide and metformin. Results: Although hyperaemic MBF did not differ significantly between the patients and controls (1.81 (0.38) v 1.97 (0.43) ml/min/g; mean (SD)), the CPT-induced MBF increase (ΔMBF) was significantly less in diabetic patients than in controls (0.07 (0.07) v 0.25 (0.12) ml/min/g; p<0.001). Treatment with glyburide and metformin significantly decreased plasma glucose concentrations from 207 (76) to 134 (52) mg/dl (p<0.001). This decrease in plasma glucose was paralleled by a significant increase in ΔMBF in response to CPT (0.20 (0.16) from 0.07 (0.07) ml/min/g; p<0.001), which tended to be lower than in controls at baseline (0.20 (0.16) v 0.25 (0.12) ml/min/g; p u200a=u200a NS). The decrease in plasma glucose concentrations correlated significantly with the improvement in ΔMBF in response to CPT (ru200a=u200a0.67, p<0.01). Conclusions: Type 2 diabetes mellitus is associated with abnormal MBF response to CPT, which can be significantly improved by euglycaemic control with glyburide and metformin. The close association between the decrease in plasma glucose concentration and the improvement in coronary vasomotor function in response to CPT suggests a direct adverse effect of raised plasma glucose concentration on diabetes-related coronary vascular disease.

PET-measured heterogeneity in longitudinal myocardial blood flow in response to sympathetic and pharmacologic stress as a non-invasive probe of epicardial vasomotor dysfunction

PurposeWe investigated whether a myocardial perfusion gradient during pharmacologically induced hyperemia also occurred during sympathetic stimulation with cold pressor testing (CPT), which commonly induces a paradoxical coronary vasoconstriction in individuals with coronary risk factors.MethodsMyocardial blood flow (MBF) was measured in absolute units (ml/g/min) with 13N-ammonia and PET at rest, during CPT, and during pharmacologic vasodilation in 59 participants with coronary risk factors (“at risk”) and in 43 healthy individuals (controls). MBF was assessed globally as mean MBF, and in the mid and mid-distal myocardium of the left ventricle (LV). A decrease in MBF from mid to mid-distal LV myocardium was defined as MBF difference indicative of a perfusion gradient.ResultsThe change in mean MBF to CPT (ΔMBF) in the at-risk group was significantly reduced compared with controls (0.05±0.19 vs 0.31±0.20xa0ml/g/min, p<0.0001), whereas mean MBF during pharmacologic vasodilation in the at-risk group tended to be lower than in controls (1.72±0.71 vs 2.00±0.64xa0ml/g/min, p=NS). Absolute MBFs during CPT and pharmacologic vasodilation were significantly lower in the mid-distal than in the mid LV myocardium, resulting in a significant MBF difference in the at-risk group (0.15±0.06 and 0.27±0.12xa0ml/g/min, p<0.0001) that was not observed in controls (0.007±0.05 and 0.014±0.10xa0ml/g/min, p=NS). In the at-risk group there was a significant correlation between the difference of mid to mid-distal MBF during CPT and that during pharmacologic vasodilation (r=0.43, p<0.004), suggesting functional alterations of epicardial vessels as the predominant cause for the observed MBF difference.ConclusionThe relative decrease in MBF from the mid to the mid-distal left-ventricular myocardium suggests an intracoronary pressure decline during CPT and pharmacologic vasodilation, which is likely to reflect an impairment of flow-mediated epicardial vasomotor function.

Effect of hormone replacement therapy on vasomotor function of the coronary microcirculation in post-menopausal women with medically treated cardiovascular risk factors

AIMSnThe aim of this study was to evaluate the effect of hormone replacement therapy (HRT) on coronary vasomotor function in post-menopausal women (PM) with medically treated cardiovascular risk factors (RFs) in a cross-sectional and a longitudinal follow-up (FU) study.nnnMETHODS AND RESULTSnMyocardial blood flow (MBF) response to cold pressor testing (CPT) and during pharmacologically induced hyperaemia was measured with positron emission tomography in pre-menopausal women (CON), in PM with HRT and without HRT, and repeated in PM after a mean FU of 24 +/- 14 months. When compared with CON at baseline, the endothelium-related change in MBF (DeltaMBF) to CPT progressively declined in PM with HRT and without HRT (0.35 +/- 0.23 vs. 0.24 +/- 0.20 and 0.16 +/- 0.12 mL/g/min; P = 0.171 and P = 0.021). In PM without HRT and in those with HRT at baseline but with discontinuation of HRT during FU, the endothelium-related DeltaMBF to CPT was significantly less at FU than at baseline (0.05 +/- 0.19 vs. 0.16 +/- 0.12 and -0.03 +/- 0.14 vs. 0.25 +/- 0.18 mL/g/min; P = 0.023 and P = 0.001), whereas no significant change was observed in PM with HRT (0.19 +/- 0.22 vs. 0.23 +/- 0.22 mL/g/min; P = 0.453). Impaired hyperaemic MBFs when compared with CON were not significantly altered from those at baseline exam.nnnCONCLUSIONnLong-term administration of oestrogen may contribute to maintain endothelium-dependent coronary function in PM with medically treated cardiovascular RFs.

Influence of dietary state and insulin on myocardial, skeletal muscle and brain [18F]-fluorodeoxyglucose kinetics in mice

BackgroundWe evaluated the effect of insulin stimulation and dietary changes on myocardial, skeletal muscle and brain [18F]-fluorodeoxyglucose (FDG) kinetics and uptake in vivo in intact mice.MethodsMice were anesthetized with isoflurane and imaged under different conditions: non-fasted (n = 7; controls), non-fasted with insulin (2 IU/kg body weight) injected subcutaneously immediately prior to FDG (n = 6), fasted (n = 5), and fasted with insulin injection (n = 5). A 60-min small-animal PET with serial blood sampling and kinetic modeling was performed.ResultsWe found comparable FDG standardized uptake values (SUVs) in myocardium in the non-fasted controls and non-fasted-insulin injected group (SUV 45-60 min, 9.58 ± 1.62 vs. 9.98 ± 2.44; p = 0.74), a lower myocardial SUV was noted in the fasted group (3.48 ± 1.73; p < 0.001). In contrast, the FDG uptake rate constant (Ki) for myocardium increased significantly by 47% in non-fasted mice by insulin (13.4 ± 3.9 ml/min/100 g vs. 19.8 ± 3.3 ml/min/100 g; p = 0.030); in fasted mice, a lower myocardial Ki as compared to controls was observed (3.3 ± 1.9 ml/min/100 g; p < 0.001). Skeletal muscle SUVs and Ki values were increased by insulin independent of dietary state, whereas in the brain, those parameters were not influenced by fasting or administration of insulin. Fasting led to a reduction in glucose metabolic rate in the myocardium (19.41 ± 5.39 vs. 3.26 ± 1.97 mg/min/100 g; p < 0.001), the skeletal muscle (1.06 ± 0.34 vs. 0.34 ± 0.08 mg/min/100 g; p = 0.001) but not the brain (3.21 ± 0.53 vs. 2.85 ± 0.25 mg/min/100 g; p = 0.19).ConclusionsChanges in organ SUVs, uptake rate constants and metabolic rates induced by fasting and insulin administration as observed in intact mice by small-animal PET imaging are consistent with those observed in isolated heart/muscle preparations and, more importantly, in vivo studies in larger animals and in humans. When assessing the effect of insulin on the myocardial glucose metabolism of non-fasted mice, it is not sufficient to just calculate the SUV - dynamic imaging with kinetic modeling is necessary.

Cardiovascular transit times in mice by high temporal resolution microPET

In this study, we evaluated the temporal resolution of a new microPET system in mice. We then applied the high resolution capability for determining the cardiovascular transit time which is an important physiological parameter in the study of animal models of cardiovascular disease. Two groups of mice, group 1 (n=12) with high body weight and group 2 (n=10) with low body weight, were studied. Each mouse was injected with a 18F-deoxyglucose (FDG; 40-50 /spl mu/L; 8-48 MBq) bolus and a list mode PET acquisition was started. MicroCT was performed for attenuation correction. We histogrammed the first 9 seconds of the list mode data into frames of 0.2 s-0.5 s duration. After the images were reconstructed and attenuation corrected, the ROIs were assigned to the following structures: vena cava, right and left ventricle blood pool (RV&LV), left lung and aorta. A time activity curve (VAC) of each ROI was generated. To correct for the recirculation, the end of each TAC was approximated by an exponential decay curve. The transit time (TT) was then calculated as the difference of the mean arrival times of the bolus in RV and LV. Short time frames of 0.3 s proved to be the best in terms of reducing noise and at the same being able to follow the rapid physiological processes. The peaks of the TACs showed good separation in various structures if the time spread of the bolus in the vena cava measured as full width of half maximum (FWHM) was shorter than 2 s. Group 1 had significantly (p<0.05) longer TT as expected than those of group 2.