Nature of the Active Sites on Ni/CeO2 Catalysts for Methane Conversions

Effective catalysts for the direct conversion of methane to methanol and for methane’s dry reforming to syngas are Holy Grails of catalysis research toward clean energy technologies. It has recently been discovered that Ni at low loadings on CeO₂(111) is very active for both of these reactions. Revealing the nature of the active sites in such systems is paramount to a rational design of improved catalysts. Here, we correlate experimental measurements on the CeO₂(111) surface to show that the most active sites are cationic Ni atoms in clusters at step edges, with a small size wherein they have the highest Ni chemical potential. We clarify the reasons for this observation using density functional theory calculations. Focusing on the activation barrier for C–H bond cleavage during the dissociative adsorption of CH₄ as an example, we show that the size and morphology of the supported Ni nanoparticles together with strong Ni-support bonding and charge transfer at the step edge are key to the high catalytic activity. We anticipate that this knowledge will inspire the development of more efficient catalysts for these reactions.

Reaction Pathway for Coke-Free Methane Steam Reforming on a Ni/CeO2 Catalyst: Active Sites and the Role of Metal-Support Interactions

Methane steam reforming (MSR) plays a key role in the production of syngas and hydrogen from natural gas. The increasing interest in the use of hydrogen for fuel cell applications demands development of catalysts with high activity at reduced operating temperatures. Ni-based catalysts are promising systems because of their high activity and low cost, but coke formation generally poses a severe problem. Studies of ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) indicate that CH₄/H₂O gas mixtures react with Ni/CeO₂(111) surfaces to form OH, CH_x, and CH_xO at 300 K. All of these species are easy to form and desorb at temperatures below 700 K when the rate of the MSR process is accelerated. Density functional theory (DFT) modeling of the reaction over ceria-supported small Ni nanoparticles predicts relatively low activation barriers between 0.3 and 0.7 eV for complete dehydrogenation of methane to carbon and the barrierless activation of water at interfacial Ni sites. Hydroxyls resulting from water activation allow for CO formation via a COH intermediate with a barrier of about 0.9 eV, which is much lower than that through a pathway involving lattice oxygen from ceria. Neither methane nor water activation is a rate-determining step, and the OH-assisted CO formation through the COH intermediate constitutes a low-barrier pathway that prevents carbon accumulation. The interactions between Ni and the ceria support and the low metal loading are crucial for the reaction to proceed in a coke-free and efficient way. These results pave the way for further advances in the design of stable and highly active Ni-based catalysts for hydrogen production.

Ce=O Terminated CeO2

Multiply bonded lanthanide oxo groups are rare in coordination compounds and have not previously been reported for a surface termination of a lanthanide oxide. Here we report the observation of a Ce=O terminated ceria surface in a CeO2 (111)-( 3 × 3 )R30° reconstruction of ≈3 nm thick ceria islands prepared on Pt(111). This is evidenced by scanning tunnelling microscopy (STM), low energy electron diffraction (LEED) and high-resolution electron energy loss spectroscopy (HREELS) measurements in conjunction with density functional theory (DFT) calculations. A Ce=O stretching frequency of 775 cm-1 is observed in HREELS, compared with 766 cm-1 calculated by DFT. The calculations also predict that the Ce=O bond is weak, with an oxygen vacancy formation energy of 0.85 eV. This could play an important role in the facile removal of lattice oxygen from CeO2 , accompanied by the reduction of CeIV to CeIII , which is a key attribute of ceria-based systems in connection with their unique catalytic properties.

Reimagining physiology education with interactive content developed in H5P

The amalgamation of educational technologies in higher education is widespread and has become essential for contemporary practice on a large scale. Foundational anatomy and physiology knowledge is integral to all courses in health education. To tackle the volume and complexity of the content taught at the foundation level, the incorporation of online tools embedded within curricula provides a unique opportunity to engage students through active learning strategies in a blended design (Means B, Toyama Y, Murphy R, Baki M. Teach Coll Rec 115: 1-47, 2013). This article reports on the use of H5P as a platform to foster self-paced and self-directed learning, critically outlining the developmental process involved in scaffolding activities to learning outcomes. The H5P activities were embedded within the online learning management system, which enabled tracking of student access to these resources. Students were asked to complete an online survey about their perspectives on the effectiveness of H5P activities. This work is part of a comprehensive study evaluating the blended design for delivery of first-year physiology subjects.

DFT insights into structural effects of Ni-Cu/CeO2 catalysts for CO selective reaction towards water-gas shift

The water-gas shift (WGS) reaction is a key step in hydrogen production, particularly to meet the high-purity H2 requirement of PEM fuel cells. The catalysts currently employed in large-scale WGS plants require a two-step process to overcome thermodynamic and kinetic limitations. Ni-Cu/CeO2 solids are promising catalysts for the one-step process required for small-scale applications, as the addition of Cu hinders undesired methanation reactions occurring on Ni/CeO2. In this work, we performed calculations on Ni4-xCux/CeO2(111) systems to evaluate the influence of cluster conformation on the selectivity towards water-gas shift. The structure and miscibility of CeO2-supported Ni4-xCux clusters were investigated and compared with those of gas-phase clusters to understand the effect of metal-support interactions. The adsorption of CO onto apical Ni and Cu atoms of Ni4-xCux/CeO2(111) systems was studied, and changes in the C-O bond strength were confirmed at the electronic level by investigating shifts in the 3σ and 1π orbitals. The selectivity towards WGS was evaluated using Brønsted-Evans-Polanyi relations for the C-O activation energy. Overall, a strengthening of the C-O bond and an increase in CO dissociation energy were verified on Cu-containing clusters, explaining the improvement in selectivity of Ni4-xCux/CeO2(111) systems.

Genomic signature of successful colonization of Eurasia by the allopolyploid shepherd's purse (Capsella bursa-pastoris)

Polyploidization is a dominant feature of flowering plant evolution. However, detailed genomic analyses of the interpopulation diversification of polyploids following genome duplication are still in their infancy, mainly because of methodological limits, both in terms of sequencing and computational analyses. The shepherd's purse (Capsella bursa-pastoris) is one of the most common weed species in the world. It is highly self-fertilizing, and recent genomic data indicate that it is an allopolyploid, resulting from hybridization between the ancestors of the diploid species Capsella grandiflora and Capsella orientalis. Here, we investigated the genomic diversity of C. bursa-pastoris, its population structure and demographic history, following allopolyploidization in Eurasia. To that end, we genotyped 261 C. bursa-pastoris accessions spread across Europe, the Middle East and Asia, using genotyping-by-sequencing, leading to a total of 4274 SNPs after quality control. Bayesian clustering analyses revealed three distinct genetic clusters in Eurasia: one cluster grouping samples from Western Europe and Southeastern Siberia, the second one centred on Eastern Asia and the third one in the Middle East. Approximate Bayesian computation (ABC) supported the hypothesis that C. bursa-pastoris underwent a typical colonization history involving low gene flow among colonizing populations, likely starting from the Middle East towards Europe and followed by successive human-mediated expansions into Eastern Asia. Altogether, these findings bring new insights into the recent multistage colonization history of the allotetraploid C. bursa-pastoris and highlight ABC and genotyping-by-sequencing data as promising but still challenging tools to infer demographic histories of selfing allopolyploids.

Limited genomic consequences of mixed mating in the recently derived sister species pair, Collinsia concolor and Collinsia parryi

Highly selfing species often show reduced effective population sizes and reduced selection efficacy. Whether mixed mating species, which produce both self and outcross progeny, show similar patterns of diversity and selection remains less clear. Examination of patterns of molecular evolution and levels of diversity in species with mixed mating systems can be particularly useful for investigating the relative importance of linked selection and demographic effects on diversity and the efficacy of selection, as the effects of linked selection should be minimal in mixed mating populations, although severe bottlenecks tied to founder events could still be frequent. To begin to address this gap, we assembled and analysed the transcriptomes of individuals from a recently diverged mixed mating sister species pair in the self-compatible genus, Collinsia. The de novo assembly of 52 and 37 Mbp C. concolor and C. parryi transcriptomes resulted in ~40 000 and ~55 000 contigs, respectively, both with an average contig size ~945. We observed a high ratio of shared polymorphisms to fixed differences in the species pair and minimal differences between species in the ratio of synonymous to replacement substitutions or codon usage bias implying comparable effective population sizes throughout species divergence. Our results suggest that differences in effective population size and selection efficacy in mixed mating taxa shortly after their divergence may be minimal and are likely influenced by fluctuating mating systems and population sizes.

Antimicrobial therapy for pulmonary pathogenic colonisation and infection by Pseudomonas aeruginosa in cystic fibrosis patients

Pseudomonas aeruginosa colonisation has a negative effect on pulmonary function in cystic fibrosis patients. The organism can only be eradicated in the early stage of colonisation, while reduction of bacterial density is desirable during chronic colonisation or exacerbations. Monthly, or at least 3-monthly, microbiological culture is advisable for patients without previous evidence of P. aeruginosa colonisation. Cultures should be performed at least every 2-3 months in patients with well-established colonisation, and always during exacerbations or hospitalisations. Treatment of patients following the first isolation of P. aeruginosa, but with no clinical signs of colonisation, should be with oral ciprofloxacin (15-20 mg/kg twice-daily for 3-4 weeks) plus inhaled tobramycin or colistin (intravenous treatment with or without inhaled treatment can be used as an alternative), while patients with acute infection should be treated for 14-21 days with high doses of two intravenous antimicrobial agents, with or without an inhaled treatment during or at the end of the intravenous treatment. Maintenance treatment after development of chronic P. aeruginosa infection/colonisation (pathogenic colonisation) in stable patients (aged>6 years) should be with inhaled tobramycin (300 mg twice-daily) in 28-day cycles (on-off) or, as an alternative, colistin (1-3 million units twice-daily). Colistin is also a possible choice for patients aged<6 years. Treatment can be completed with oral ciprofloxacin (3-4 weeks every 3-4 months) for patients with mild pulmonary symptoms, or intravenously (every 3-4 months) for those with severe symptoms or isolates with ciprofloxacin resistance. Moderate and serious exacerbations can be treated with intravenous ceftazidime (50-70 mg/kg three-times-daily) or cefepime (50 mg/kg three-times-daily) plus tobramycin (5-10 mg/kg every 24 h) or amikacin (20-30 mg/kg every 24 h) for 2-3 weeks. Oral ciprofloxacin is recommended for patients with mild pulmonary disease. If multiresistant P. aeruginosa is isolated, antimicrobial agents that retain activity are recommended and epidemiological control measures should be established.

Prevalence and risk of cysticercosis and taeniasis in an urban population of soldiers and their relatives

To determine markers of Taenia solium transmission and risk factors in an urban community, we studied 1,000 soldiers from a military camp in Mexico City and their relatives. Serum samples were used to detect antigens and antibodies and fecal specimens were examined for Taenia coproantigens and helminth eggs. Prevalences of 12.2% and 5.8% for cysticercosis were found among soldiers and their relatives, respectively. Taeniasis was found in 0.5% and none of the groups, respectively. Relatives of soldiers positive for cysticercosis and taeniasis markers ate more pork from street stores than restaurants or markets compared with relatives of soldiers without these indicators of infection. Also, 12.0% of the relatives of positive soldiers had a history of expelling tapeworm proglottids in the feces in contrast to 3.7% of the family members of the control group. Prevalence values and risk factors in this urban population are similar to those of previous studies performed in rural populations.

[Atherosclerotic coronary ectasia or a lymphomucocutaneous syndrome in an adult (Kawasaki's disease)?]

We report the case of a 42-year-old man, who was admitted to hospital with an inferior myocardial infarction. He was treated with tissue plasminogen activator without complications in the acute phase. The stress testing performed before discharge showed residual myocardial ischemia. A catheterization study was indicated. The coronary angiogram demonstrated diffuse three vessel coronary artery aneurysmal disease. Two years before the patient had an aneurysm of the right iliac artery being operated on. The differential diagnosis of adult aneurysmal coronary disease is discussed with emphasis on Kawasaki's disease and atherosclerotic coronary artery ectasia.

[Thrombus in the thoracic aorta as cause of peripheral embolism diagnosed using transesophageal echocardiography]

The authors report the cases of two patients, with no risk factors for thromboembolism, in whom a mobile thrombus of the thoracic aorta was diagnosed by transesophageal echocardiography, after an episode of systemic embolism. The outcomes of the two cases were very different. In one patient the thrombus was no longer present after anticoagulant treatment with no recurrent embolic event. The other patient had a new embolic event and the thrombus persisted while having anticoagulant therapy. This patient underwent surgery, and the thrombus was removed. These cases illustrate the value of transesophageal echocardiography in the detection of embolic source.

[Risk factors in stable coronary disease. Relationship with ischemic threshold and prognostic implications]

BACKGROUND

To assess the clinical evolution, in a 5-year follow-up, of the development of acute coronary syndromes, in patients with angina clinically stable, establishing its relationship with the ischemic threshold (IT) and the main modifiable cardiovascular risk factors.

PATIENTS AND METHODS

120 patients, 86 males (71%), with an age of 57 +/- 8 years, with stable angina. The presence of smoking, hypercholesterolemia, hypertension and diabetes mellitus was evaluated. We performed exercise testings (baseline and after vasodilator drugs) in the beginning, in order to characterize the IT (which was fixed in 72 patients and variable in 48). The later group underwent exercise testing each term during the first year of follow-up. Lesion at least of 70% in a main coronary vessel was required as inclusion criteria. The development of acute myocardial infarction (AMI), unstable angina pectoris and cardiac death was recorded. Cox's hazard function analysis and multivariant analysis were applied.

RESULTS

106 patients (88%) had one or more risk factors (40% hypertension, 43% hypercholesterolemia, 22% diabetes mellitus and 56% were smokers or ex-smokers). A significant association was shown between male gender and smoking and diabetes mellitus and female gender. 6 cardiac deaths, 8 AMI and 9 unstable angina were recorded. Within the 72 patients with fixed IT, 12.5% (9) suffered some acute syndrome. In the 48 with variable IT, in the 30 who continued in it, 20% (6) developed acute coronary pathology and in the 18 who modified their IT to fixed, the prevalence was 44.5% (8). Patients with modification of IT to fixed had a higher risk of acute coronary syndrome in the follow-up (p < 0.01) and the presence of hypertension and hypercholesterolemia allowed the prediction of modification of the IT.

CONCLUSIONS

The prevalence of cardiovascular risk factors in the stable coronary artery disease is high (88%); male gender is associated smoking and female gender to diabetes mellitus. The presence of hypertension and hypercholesterolemia are associated to modification in the IT in patients with variable threshold, allowing the detection of a subgroup of high risk for the development of acute coronary pathology.

Classification of hypertensive cardiomyopathy

A clinical pathophysiological classification of hypertensive cardiomyopathy has been established on the basis of the degree to which the heart is affected by chronic, systemic arterial hypertension: Degree I: Asymptomatic patients without left ventricular hypertrophy but with left ventricular diastolic dysfunction according to Doppler mitral inversion relation (E/A < 0.9) or to gamma scintigraphy (peak filling rate reduction < or = 2.7 EDC.s-1. These patients are classified as Group 1. Degree II: Asymptomatic or mildly symptomatic patients (New York Heart Association class I) with echocardiographic left ventricular hypertrophy; classified as Group IIA or IIB according to whether weight-adjusted maximal oxygen uptake is normal or below normal, respectively. Degree III: The basic characteristic is the presence of congestive heart failure with normal ejection fraction (EF > or = 50%). Two subsets can be distinguished on the basis of degree of hypertrophy: Group IIIA, with a mass/volume index > 1.8, and IIIB with a mass/volume index < 1.8. The differences between the two are as follows: patients classified as IIIA had a lower rate of regional ischaemia, a higher ejection fraction, a more frequently audible fourth sound, rarely a third sound and a cardiothoracic ratio < 0.5; IIIB patients had a higher prevalence of regional ischaemia (thallium-positive), a frequently audible third sound and a cardiothoracic ratio > 0.5. Degree IV: This category is characterized by the presence of depressed contractility, which could cause heart failure, by an ejection fraction < 50% and an increase in ventricular volumes. Echocardiography shows increased distance between mitral point E and the septum.

[The effect of antihypertensive therapy on left ventricular mass and diastolic filling in light and moderate hypertension]

BACKGROUND

To valorate the effect of four antihypertensive drugs on the regression of cardiac mass and diastolic function, by echocardiography-Doppler, in not treated hypertensive subjects.

METHODS

60 mild-moderate hypertensive subjects were studied randomized in four groups of 15 patients each one: enalapril (10-40 mg/d), atenolol (25-100 mg/d), verapamil-retard (120-240 mg/d), alphametildopa (250 mg/8h to 3 g/d). The active drug therapy phase was 6 months, performing echo-Doppler, evaluating posterior-wall and septal-wall thicknesses, ventricular mass index, ratio of early to atrial peak diastolic filling velocity (E/A), the first-third filling fraction and atrial filling fraction.

RESULTS

The cardiac mass index decreased with the four drugs: with enalapril from 178 +/- 28 to 155 +/- 29 g/m2 (p < 0.05), with atenolol from 170 +/- 23 to 154 +/- 19 g/m2 (p < 0.05), with verapamil from 180 +/- 27 to 159 +/- 22 g/m2 (p < 0.05) and with alphametildopa from 176 +/- 30 to 142 +/- 22 g/m2 (p < 0.01). The E/A ratio and first-third filling fraction only improved in the atenolol subgroup, from 0.79 +/- 0.13 to 0.97 +/- 0.16 (p < 0.01) and from 36 +/- 5 to 44 +/- 9% (p < 0.01), decreasing atrial filling fraction from 37 +/- 6 to 30 +/- 8% (p < 0.01), without modifying with enalapril (0.74 +/- 0.14 to 0.76 +/- 0.20, 35 +/- 5% to 36 +/- 7%, 38 +/- 5 to 39 +/- 7%, p = NS), verapamil (0.69 +/- 0.12 to 0.74 +/- 0.17, 35 +/- 6% to 36 +/- 8% to 40 +/- 12%, p = NS) neither alphametildopa (0.72 +/- 0.14 to 0.71 +/- 0.21, 34 +/- 5% to 35 +/- 7%, 40 +/- 6% to 41 +/- 9%, p = NS). The heart rate decreased more with atenolol than with the other drugs (61 +/- 15 vs 71 +/- 12, p < 0.01).

CONCLUSIONS

In hypertensive patients the decreasing of cardiac mass is not accompanied of improvement of the diastolic function except in patients treated with atenolol, probably due to bradycardia.

Usefulness of exercise testing performed with vasodilators for predicting the severity of myocardial ischaemia during daily activities and treatment

Fifty patients (aged 53 +/- 7 years) with confirmed coronary disease performed two stress tests (baseline and following treatment with vasodilators) and were divided into two groups: (A) fixed ischaemic threshold (n = 27), and (B) variable ischaemic threshold (n = 23). All patients underwent 24-h baseline Holter monitoring and monitoring following treatment with nifedipine, placebo, propranolol and nifedipine + propranolol. In Group A, 92% of ischaemic episodes occurred at heart rates similar to those found during exercise testing. In Group B, the heart rate was lower in 66%. In Group A, positive stress testing before the first 3 min of exercise, or at < 140 beat,min-1 with ST segment depressions > or = 0.02 mV, correlated with higher Holter indexes. In Group A, propranolol reduced both the number of episodes and total ischaemia time. In Group B, the best effects were achieved with nifedipine and combined treatment. Our results further emphasize the contrasts between patients with angina and fixed and variable ischaemic thresholds and suggest that therapy tailored to the physiopathology may be most efficacious.

Congestive heart failure from left ventricular diastolic dysfunction in systemic hypertension

Previous studies have pointed out that congestive heart failure (CHF) with normal ejection fraction presents a uniform clinical profile that is indistinguishable from heart failure with low ejection fraction. Thirty-six patients with systemic hypertension who had recently experienced CHF with normal ejection fraction (> or = 50%) and no clinical history of ischemic cardiomyopathy were studied. The patients were divided into 2 groups according to degree of echocardiographic hypertrophy: group A (19 patients) with a ventricular mass/volume ratio > 1.8, and group B (17 patients) with a ratio < 1.8. Group A patients had a higher ejection fraction (67 +/- 6 vs 57 +/- 3%, p < 0.01), smaller ventricular diameters and a lower thallium-201 positive rate at peak stress (10 vs 70% in group B, p < 0.001), with 8 of 10 showing severe coronary stenosis. Clinically, group A had a more frequent audible fourth sound (79 vs 17%, p < 0.001), a low incidence of audible third sound (5 vs 55%, p < 0.001) and a cardiothoracic ratio < or = 0.5 (63 vs 17%, p < 0.01). The degree of radionuclide-detected resting diastolic dysfunction and exercise intolerance was similar in both groups. In conclusion, CHF with normal ejection fraction in hypertensive patients presents 2 different profiles: one characterized by severe hypertrophy and the other by a high rate of myocardial regional ischemia. Therapy should be aimed at pathophysiologic regression of the hypertrophy in the first case, and at improvement of the ischemia in the second.

Treatment of transient myocardial ischemia in patients with stable angina: a comparative study of verapamil slow-release and nifedipine plus propranolol

We compared the effect of verapamil slow-release (VSR) and the combination of nifedipine plus propranolol on transient myocardial ischemia in a double-blind study comprising 20 patients with proven coronary artery disease and chronic stable angina. According to the results of 24-h Holter-monitoring recording, patients were divided into two groups: 10 patients with fixed coronary reserve and 10 patients with variable coronary reserve. The number of ischemic events was reduced with both therapies: from 12 +/- 10 at baseline to 3.4 +/- 4.0 (p less than 0.05) with verapamil and to 3.9 +/- 7.0 (p less than 0.05) with nifedipine plus propranolol (N + P). When total ischemic burden was measured, findings were similar: It was reduced from 104 +/- 196 min to 27 +/- 57 (p less than 0.05) with N + P and to 17 +/- 18 min with verapamil in patients with fixed coronary reserve and from 36 +/- 44 to 5 +/- 9 min (p less than 0.05) with verapamil and to 5 +/- 10 min with N + P in patients with a variable coronary reserve. VSR shows antiischemic efficacy similar to that of the combination of N + P in treatment of transient myocardial ischemia in patients with stable angina.

[The 2-dimensional and Doppler color echocardiographic study of a congenital aneurysm of the sinus of Valsalva with a fistula of the right atrium in an adult]

This report describe a 69-year old woman with a congenital aneurysm of the non-coronary sinus of Valsalva ruptured in the right atrium, causing severe hemodynamic derangement of the right ventricle. The site of the communication between the aneurysm and the receiving chamber was accurately diagnosed by two-dimensional color flow Doppler imaging which provided more valuable preoperative information than conventional aortography.

[Doppler analysis of mitral flow in mild to moderate hypertension]

We evaluate by Echo-Doppler the left ventricular relaxation disturbance produced by mild to moderate hypertension. It's a comparative study between 15 healthy and 40 patients with hypertension (diastolic blood pressure between 90-114 mmHg and/or systolic greater than 160 mmHg). Echocardiography was performed in all cases and diameters, thickness, volumes, ejection fraction, mass, transmitral flow by Doppler and cardiac output were evaluated . In hypertensive patients the septal and posterior wall thicknesses were significantly higher (1.39 +/- 0.2 cm vs 1.1 +/- 0.1, p less than 0.001 cm. and 1.26 +/- 0.12 cm vs 0.98 +/- 0.1 cm, p less than 0.001), and also the absolute mass and corrected according to corporal surface (339 +/- 58 g vs 203 +/- 44, p less than 0.001, and 185 +/- 34 g/m2 vs 115 +/- 16, p less than 0.001). In transmitral flow Doppler the higher isovolumetric period and lower diastolic filling in the first 1/3 (71 +/- 19 msec vs 53 +/- 20, p less than 0.05, and 35 +/- 5% vs 52 +/- 4%, p less than 0.001) are indicators of relaxation disturbance. A lower deceleration of early inflow and a higher deceleration time (265 +/- 98 cm/sec2/vs 454 +/- 139, p less than 0.001, and 226 +/- 38 msec vs 156 +/- 15, p less than 0.001) show compliance damage. The atrial filling was significantly higher in hypertensive patients (37 +/- 7% vs 20 +/- 8%, p less than 0.001). The E/A ratio, separate both groups but corrected by the age the signification was rather lower.(ABSTRACT TRUNCATED AT 250 WORDS)

[Prognostic significance of the electrocardiographic coronary reserve in stable angina]

We've studied the prognostic significance of the electrocardiographic coronary reserve, evaluated by seried effort tests, in patients with stable angina and proved coronary disease. Seventy-three patients with stable angina, who performed 2 exercise tests (basal and after vasodilator therapy) were included. It's considered variable reserve when in the second test the ST-descent improves greater than or equal to 1 mm for equal or higher double product (43 patients) and fixed reserve when it doesn't (30 patients). All of them underwent to coronariography study. The exercise test was seried each term during the first year. Clinical follow-up lasted 3 years and we considered cardiac events: myocardial infarction, unstable angina, surgery, PTCA or death. Patients with fixed reserve had higher maximal ST-descent (2.5 +/- 0.7 vs 1.9 +/- 0.6; p less than 0.05), lesser effort-time (359 +/- 144 vs 430 +/- 112; p less than 0.05), and more severe coronary disease (score: 3.5 +/- 1.5 vs 2.4 +/- 0.8; p less than 0.01) as compared with variable reserve group. Unfavorable clinic evolution was similar in both groups (44.3% in the fixed reserve group and 34.8% in the variable reserve group). We verified that 92.3% of patients with variable reserve who didn't modify its character in a year had good evolution; 76.4% of patients who changed to fixed reserve had unfavorable evolution (significant association, p less than 0.01). We conclude that in patients with variable reserve, the periodic evaluation of the reserve character has important prognostic implication.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral blood flow and metabolism during hypoglycemia in newborn dogs

Cerebral blood flow (CBF) and cerebral metabolic rates (CMR) were studied in newborn dogs during insulin-induced hypoglycemia. Pups were anesthetized, paralyzed, and artificially ventilated with a mixture of 70% nitrous oxide and 30% oxygen to maintain normoxia and normocarbia. Experimental animals were given regular insulin (0.3 units/gm IV); controls received normal saline. CBF was determined using a modification of the Kety-Schmidt technical employing 133Xe as indicator. Arteriovenous differences for oxygen, glucose, lactate, and beta-hydroxybutyrate (beta-OHB) were also measured, and CMRO2 and CMRsubstrates calculated. Two groups of hypoglycemic dogs were identified; those in which blood glucose levels were greater than 0.5 mM (group 1), and those in which they were less than 0.5 mM (group 2). CBF did not change significantly from control values of 23 +/- 10 ml/min/100 g (mean +/- S.D.) at both levels of hypoglycemia. Similarly, hypoglycemia did not alter CMRO2 significantly from its initial level of 1.05 +/- 0.37 ml O2/min/100 g. Glucose consumption in brain during normoglycemia accounted for 95% of cerebral energy supply with minimal contributions from lactate (4%) and beta-OHB (0.5%). During hypoglycemia, CMRglucose declined by 29 and 52% in groups 1 and 2, respectively, while CMRlactate increased to the extent that this metabolite became the dominant fuel for oxidative metabolism in brain. The cerebral utilization of beta-OHB was unaltered by hypoglycemia. The findings indicate that insulin-induced hypoglycemia in the newborn dog is associated with an increase in cerebral lactate utilization, supplementing glucose as the primary energy fuel and thereby preserving a normal CMRO2. These metabolic responses may contribute to the tolerance of the immature nervous system to the known deleterious effects of hypoglycemia.