Comparison of caffeine-induced changes in cerebral blood flow and middle cerebral artery blood velocity shows that caffeine reduces middle cerebral artery diameter

Changes in cerebral blood flow (CBF) can be assessed directly with xenon clearance (XeC) or indirectly by measuring changes in middle cerebral artery blood velocity (Vmca) with transcranial Doppler (TCD). The aim of this study was to compare the changes in CBF and Vmca following caffeine ingestion. Nineteen patients (age 48–86, recovering from an acute stroke) and ten controls (age 52–85) were each studied twice. Bilateral measurements of CBF and Vmca were made before and after ingestion of 250 mg caffeine or matched placebo. The percentage change in CBF and Vmca after caffeine was calculated. Full results (CBF and Vmca) were obtained from 14 patients and 9 controls. There was no significant difference between patients and controls, so results were combined. Caffeine reduced CBF by 22% (95% confidence interval (CI) = 17% to 28%) and reduced Vmca by 13% (95% CI = 10% to 17%). The fall in Vmca was significantly less than that in CBF (p = 0.0016), showing that caffeine reduces mca diameter. Analysis based on Poiseuille flow in the arterioles suggests that caffeine reduced arteriole diameter by 5.9% (95% CI = 4.6% to 7.3%) and mca diameter by 4.3% (95% CI = 2.0% to 6.6%). TCD is being used as an alternative to XeC for assessing the effect of vasoconstrictors and vasodilators on CBF. This study has demonstrated that mca diameter can be changed by the vasoactive agents, and that changes in Vmca do not necessarily reflect changes in CBF

Cerebrovascular mental stress reactivity is impaired in hypertension

<p>Abstract</p> <p>Background</p> <p>Brachial artery reactivity in response to shear stress is altered in subjects with hypertension. Since endothelial dysfunction is generalized, we hypothesized that carotid artery (CA) reactivity would also be altered in hypertension.</p> <p>Purpose</p> <p>To compare (CA endothelium-dependent vasodilation in response to mental stress in normal and hypertensive subjects.</p> <p>Methods</p> <p>We evaluated CA reactivity to mental stress in 10 young healthy human volunteers (aged 23 ± 4 years), 20 older healthy volunteers (aged 49 ± 11 years) and in 28 patients with essential hypertension (aged 51 ± 13 years). In 10 healthy volunteers and 12 hypertensive subjects, middle cerebral artery (MCA) PW transcranial Doppler was performed before and 3 minutes after mental stress.</p> <p>Results</p> <p>Mental stress by Stroop color word conflict, math or anger recall tests caused CA vasodilation in young healthy subjects (0.61 ± 0.06 to 0.65 ± 0.07 cm, p < 0.05) and in older healthy subjects (0.63 ± 0.06 to 0.66 ± 0.07 cm, p < 0.05), whereas no CA vasodilation occurred in hypertensive subjects (0.69 ± 0.06 to 0.68 ± 0.07 cm; p, NS). CA blood flow in response to mental stress increased in young healthy subjects (419 ± 134 to 541 ± 209 ml, p < 0.01 vs. baseline) and in older healthy subjects (351 ± 114 to 454 ± 136 ml, p < 0.01 vs. baseline) whereas no change in blood flow (444 ± 143 vs. 458 ± 195 ml; p, 0.59) occurred in hypertensive subjects. There was no difference in the CA response to nitroglycerin in healthy and hypertensive subjects. Mental stress caused a significant increase in baseline to peak MCA systolic (84 ± 22 to 95 ± 22 cm/s, p < 0.05), diastolic (42 ± 12 to 49 ± 14 cm/s, p < 0.05) as well as mean (30 ± 13 to 39 ± 13 cm/s, p < 0.05) PW Doppler velocities in normal subjects, whereas no change in systolic (70 ± 18 to 73 ± 22 cm/s, p < 0.05), diastolic (34 ± 14 to 37 ± 14 cm/s, p = ns) or mean velocities (25 ± 9 to 26 ± 9 cm/s, p = ns) occurred in hypertensive subjects, despite a similar increase in heart rate and blood pressure in response to mental stress in both groups.</p> <p>Conclusion</p> <p>Mental stress produces CA vasodilation and is accompanied by an increase in CA and MCA blood flow in healthy subjects. This mental stress induced CA vasodilation and flow reserve is attenuated in subjects with hypertension and may reflect cerebral vascular endothelial dysfunction. Assessment of mental stress induced CA reactivity by ultrasound is a novel method for assessing the impact of hypertension on cerebrovascular endothelial function and blood flow reserve.</p

Dévitalisation chimique de souches de noisetier et de frêne

The objective of this experiment is to test 11 devitalisation treatments of stumps of hazel and ash trees. Two factors are considered: the application method (spraying after cutting, application while cutting, and washing) and the active ingredient (glyphosate, triclopyr, 2,4-D + triclopyr, ammonium sulfamate). On both species, the system whereby the active ingredient is applied while cutting is less efficient because less product is used than with a simple spray. Glyphosate is very efficient on hazel-trees. It is even better than ammonium sulfamate and triclopyr, two good products. The results are different on ash-trees: ammonium sulfamate did not yield good results while the 3 other active ingredients were very efficient. / Cet essai vise à tester 11 traitements destinés à dévitaliser des souches de noisetier et de frêne. Deux facteurs sont étudiés : le mode d'application (pulvérisation après la coupe, dépôt en même temps que la coupe, badigeonnage), la matière active (glyphosate ; triclopyr ; 2,4-D + 2,4-DP ; 2,4 - D + triclopyr ; sulfamate d'ammonium). Pour les deux essences traitées, le système permettant le dépôt en même temps que la coupe se révèle moins efficace du fait qu'il dépose moins de produit (- 43 %) que la simple pulvérisation. Sur le noisetier, le glyphosate est très efficace. Il devance le sulfamate d'ammonium et le triclopyr qui sont deux produits ayant donné d'assez bons résultats. Sur le frêne, les résultats sont différents : le sulfamate d'ammonium est décevant ; par contre, trois matières actives sont très efficaces : le glyphosate, le 2,4 - D + triclopyr et le trilopyr seul

Reactivity of cellulose in butanol isomers for its valorization in butyl levulinates.

International @ CDFA+ADO:NES:FRAInternational audienceNon

Reactivity of levulinic acid and cellulose with butenes for the formation of butyl levulinates

SSCI-VIDE+CDFA+ADO:NES:FRAInternational audienceAmong the chemicals that can be obtained from renewable biomass, levulinic esters and more especially butyl levulinates are recognized as potential alternatives to some petro-chemicals for use as additives (fuel, flagrance), solvents and also platforms for fine chemistry. Also their more interesting formation from raw biomass (cellulose) has been reported. The main route involves acid-catalyzed esterification of levulinic acid (ex-cellulose) with an alcohol.As an alternative it may be possible to form butyl levulinates using olefins instead of alcohols as alkylating agent. This would have the advantage to avoid the concomitant formation of dialkyl ether and water that limits the esterification efficiency.We will present here an in-depth study on the formation of butyl levulinates from levulinic acid and cellulose using butene isomers as alkylating reagent, in the presence of an acid catalyst.We particularly showed that the reaction can proceed in the absence of solvent. This allowed a full recovery of the formed butyl levulinates by a simple work up procedure. Stoichiometric formation is possible in a non-polar solvent able to solubilize the olefin, and even at room temperature for iso-butene. Note that it was therefore possible to obtain ter-butyl levulinate in high yields, which is not possible using tert-butanol as esterifying agent. gamma-Butyrolactone was identified as a promising green bio-based solvent needed for reaction extension to solid reactants like cellulose and preliminary results will be presented.Results of the use of solid acid catalysts will also be presented showing a high potential of efficiency and reusability under low temperature conditions

Reactivity of cellulose in butanol isomers for its valorization in butyl levulinates

National @ CDFA+ADO:NES:FRAInternational audienceNon