Structure and electron affinity of the 4H-SiC (0001) surfaces: a methodological approach for polar systems.

The ability to accurately and consistently determine the surface electronic properties of polar materials is of great importance for device applications. Polar surface modelling is fundamentally limited by the spontaneous polarisation of these materials in a periodic boundary condition scheme. Surface data are sensitive to supercell parameters, including slab and vacuum thicknesses, as well as the non-equivalence of surface adsorbates on opposite surfaces. Using 4H-SiC as a specific case, this study explores calculation of electron affinities (EAs) of (0001̄) and (0001) surfaces varying chemical termination as a function of computational parameters. We report the impact in terms of band-gap, electric fields across the vacuum and slab for single and double cell slab models, where the latter is constructed with inversional symmetry to eliminate the electric field in the vacuum regions. We find that single cells are sensitive to both slab and vacuum thickness. The band-gap narrows with slab thickness, ultimately vanishing and inducing charge transfer between opposite surfaces. This has a consequence for predicted EAs. Adsorbate species are found to play a crucial role in the rate of narrowing. Back to back cells with inversional symmetry have larger electric fields present across the slab than the single slab cases, resulting in a greater band-gap narrowing effect, but the vacuum thickness dependence is completely removed. We discuss the relative merits of the two approaches.

Silicon and germanium terminated (0 0 1)-(2 [Formula: see text] 1) diamond surface.

Control over the chemical termination of diamond surfaces has shown great promise in the realization of field-emission applications, the selection of charge states of near-surface colour-centres such as NV, and the realisation of surface-conductive channels for electronic device applications. Experimental investigations of ultra-thin Si and Ge layers yield surface states both within the band-gap and resonant with the underlying diamond valence band. In this report, we report the results of density-functional simulations of a range of coverages of Si and Ge on diamond (0 0 1) surfaces. We have found that surface coverage with crystallogen:carbon ratios of 67% and 75% are more stable than both higher and lower coverages on the (0 0 1)-diamond surface, and that they can explain the observation of an occupied band around 1.7 eV below the valence band top. We also report geometries, adsorption energies and electron affinities of these surface structures, and show that the resonant state is made up from conventional spd-covalent [Formula: see text]-bonding orbitals between the surface adsorbates.

Long-term follow-up of patients from the 1989 Q fever outbreak: no evidence of excess cardiac disease in those with fatigue.

BACKGROUND: In 1989, an outbreak of Q fever (C. burnetii infection) with 147 confirmed cases occurred in Solihull, West Midlands. Three patients developed cardiomyopathy in the subsequent 10 years. The cohort has been followed up with respect to the development of fatigue and, in this instance, cardiac effects after the original infection. AIM: To determine whether persisting fatigue after Q fever represented sub-clinical cardiomyopathy. DESIGN: Prospective follow-up study. METHODS: All traceable subjects from the original outbreak, and community age-, sex- and smoking-matched controls, were studied. Questionnaires for idiopathic fatigue, 12-lead ECG, echocardiography, spirometry and shuttle walk distance were undertaken, and a subset with CDC-defined chronic fatigue syndrome had gated cardiac scans. RESULTS: Of the original cohort, 19 had died, three had emigrated and 10 were untraceable. Of the remaining 115, 108 responded to a mailed questionnaire and 87 were investigated further, of whom 85 provided complete data. Two developed aortic valve vegetations, one of whom died. Chronic fatigue syndrome was found in 20% of cases and 5.3% of controls (including those with co-morbidities), falling to 8.2% and 0 when excluding those with co-morbidities. There were no significant differences in ECG and echocardiographic investigations or shuttle-walk distance between those with fatigue and those without. Six of the seven patients with CFS had gated cardiac scans: all were within normal limits. CONCLUSIONS: These findings do not support the existence of a sub-clinical cardiomyopathy in the patients in this cohort who suffer from fatigue after acute Q fever, although endocarditis can occur after acute infection.

Chronic fatigue following infection by Coxiella burnetii (Q fever): ten-year follow-up of the 1989 UK outbreak cohort.

BACKGROUND: Some patients exposed to Q fever (Coxiella burnetii infection) may develop chronic fatigue. AIM: To determine whether subjects involved in the West Midlands Q fever outbreak of 1989 had increased fatigue, compared to non-exposed controls, 10 years after exposure. DESIGN: Matched cohort study comparing cases to age-, sex- and smoking-history-matched controls not exposed to Q fever. METHODS: A postal questionnaire was sent to subjects at home, followed by further assessment in hospital, including a physical examination and blood tests. RESULTS: Of 108 Q-exposed subjects, 70 (64.8%) had fatigue, 37 idiopathic chronic fatigue (ICF) (34.3%), vs. 29/80 (36.3%) and 12 (15.0%), respectively, in controls. In 77 matched pairs, fatigue was commoner in Q-exposed subjects than in controls: 50 (64.9%) vs. 27 (35.1%), p<0.0001. ICF was found in 25 (32.5%) of Q-exposed patients and 11(14.3%) of controls (p=0.01). There were 36 (46.8%) GHQ cases in Q-exposed subjects, vs. 18 (23.4%) controls (p=0.004). A matched analysis of those more intensively studied showed fatigue in 48 (66.7%) Q-exposed patients and 25 (34.7%) controls, (p<0.0001), ICF in 25 (34.7%) Q-exposed and 10 (13.9%) controls (p=0.004), and chronic fatigue syndrome (CFS) in 14 (19.4%) Q-exposed patients and three (4.2%) controls (p=0.003). Thirty-four (47.2%) Q-exposed patients were GHQ cases compared to 17 (23.6%) controls (p=0.004). DISCUSSION: Subjects who were exposed to Coxiella in 1989 had more fatigue than did controls, and some fulfilled the criteria for CFS. Whether this is due to ongoing antigen persistence or to the psychological effects of prolonged medical follow-up is uncertain.

Does thrombolysis affect the prognostic value of the post-infarct exercise test?

There has been some debate on usefulness of the exercise test in risk stratification after myocardial infarction in the thrombolytic era. This was assessed in 295 patients of whom 184 were treated with thrombolysis. Each had an exercise test using a modified Naughton protocol within 14 days of acute myocardial infarction. The tests were graded as high risk positive (112), low risk positive (83), or negative (100). These gradings predicted use of multiple drug therapy (p = 0.05), severity of coronary artery disease (p < 0.01), and coronary artery bypass grafting (p < 0.01). There was no influence on heart failure, recurrent myocardial infarction or death. This was independent of the use of thrombolytic therapy. The whole group had a good prognosis with a mortality of 2.4% after 56 weeks' follow-up. The exercise test is still a useful screening test after myocardial infarction. In this study, there was a high negative predictive accuracy of 91% for any event. Its use is not altered by thrombolysis. The finding of a lack of influence of the exercise test on major events may be a reflection of the current good prognosis after myocardial infarction and the prompt use of revascularisation.

Anomalous aortic origin of the right coronary artery. An unusual cause of angina pectoris and its surgical correction.

A 45-year-old female presented with typical recent-onset exertional angina pectoris. Subsequent investigation showed that the likely cause was an aberrant origin of the right coronary artery arising from the left coronary sinus. This anomaly is uncommon and is not usually associated with angina pectoris. Surgical rerouting of the origin of the right coronary artery produced complete resolution of ischaemia.

Video-assisted thoracoscopic sympathectomy for severe intractable angina.

OBJECTIVE: Endoscopic trans-thoracic sympathectomy is a well documented, safe and successful treatment for palmar and axillary hyperhidrosis. This may also be helpful in the management of patients with intractable angina and advanced coronary disease unsuitable for coronary artery bypass graft (CABG) or percutaneous transluminal coronary angioplasty (PTCA). We evaluated video assisted thoracoscopic sympathectomy (VATS) in such patients with the aim of improving symptoms and quality of life. METHODS: Video assisted thoracoscopic sympathectomy, a minimally invasive procedure, was performed under general anaesthesia with alternating single lung ventilation. Three stab incisions were made at the level of the fourth intercostal space in the anterior and posterior axillary lines, and at the fifth intercostal space in the mid-axillary line through which an extensive thoracic sympathectomy was performed to include second to the fourth ganglia, bilaterally. RESULTS: A total of 16 patients aged 46-76 (mean 61) years were assessed for VATS. Of these 10 patients had the procedure performed; nine with previous CABG and one with diffuse coronary disease. Six patients were excluded because of an evolving MI (n = 1), left ventricular ejection fraction (LVEF) < 30% (n = 2), and chronic stable angina with no objective evidence of ischaemia (n = 3). All 10 patients had marked symptomatic improvement with reduction of both angina frequency and intensity of attacks. Mean follow-up period 11.5 months. Exercise tolerance and time to onset of angina measured on exercise treadmill was significantly increased post-VATS (P = 0.028) and maintained 1 year post-operative. CONCLUSION: VATS was associated with both reduction in angina symptoms and an increase in exercise time to onset of angina. An improved quality of life was evident.

Sotalol induced torsade de pointes.

Torsade de pointes is an uncommon ventricular tachyarrhythmia precipitated by a variety of metabolic and pharmacological conditions and requiring unconventional antiarrhythmic therapy. A case is presented demonstrating the occurrence of torsade de pointes following sotalol overdosage and specific features enabling recognition and treatment of this life-threatening arrhythmia are discussed.

Concealed post-infarction left ventricular rupture--a diagnostic dilemma.

We describe a patient with post-infarction left ventricular rupture exhibiting several atypical features. A successful outcome was achieved after serendipitous surgery.

Comparative clinical efficacy of bepridil, propranolol and placebo in patients with chronic stable angina.

A randomised double-blind parallel group study was performed to compare the clinical efficacy of bepridil, a new calcium slow channel blocker, with that of propranolol and placebo in patients with chronic stable angina of effort. Efficacy was assessed objectively by dynamic exercise testing using an upright bicycle ergometer and subjectively by patient documentation of anginal frequency and nitrate consumption. The administration of bepridil resulted in a significant improvement in physical work capacity expressed as calculated maximal oxygen uptake (Vo2 max) and exercise time. This was associated with subjective improvement in terms of reduced anginal frequency. Despite baseline differences in exercise performance and anginal frequency between the three treatment groups, the beneficial effects of bepridil were statistically significant when compared to propranolol. Although minor electrocardiographic changes were noted, no adverse effects were evident when bepridil was prescribed in doses of up to 400 mg/day over a 10 week period.

The combination of nifedipine and propranolol in the management of patients with angina pectoris.

1 A double-blind cross over study was carried out to assess the effects of the combination of nifedipine and propranolol in 25 patients with chronic stable angina pectoris at beta-adrenoceptor blockade. 2 Efficacy was judged objectively by a standardized exercise protocol using a bicycle ergometer and subjectively by patient assessment of anginal attack rate. 3 The combination of nifedipine and propranolol was shown to be effective with an increase in exercise time to angina and an increase in physical work capacity expressed in terms of calculated maximal oxygen uptake (VO2 max). There was an associated reduction in anginal attack rate. 4 The synergistic effect was even more pronounced after reduction in propranolol dosage to 50% of the beta-adrenoceptor blocking dose, reflecting the myocardial depressant effects of beta-adrenoceptor blocking drugs in these patients with coronary heart disease, some of whom had poor left ventricular function.

Right and left ventricular volumes in vitro by a new nongeometric method.

We present an evaluation of a new nongeometric technique for calculating right and left ventricular volumes. This method calculates ventricular chamber volumes from multiple cross-sectional echocardiographic views taken from a single point as the echo beam is tilted progressively through the ventricle. Right and left ventricular volumes are calculated from both the approximate short axis and approximate apical position on 20 in vitro human hearts and compared with the actual chamber volumes. The results for both ventricles from both positions are excellent. Correlation coefficients are > 0.95 for all positions; the standard errors are in the range of 5 to 7 mL and the slopes and intercepts for the regression lines are not significantly different from 1 and 0, respectively (except for the left ventricular short-axis intercept). For all positions, approximately 6 to 8 views are needed for peak accuracy (7.5 degrees to 10 degrees separation). This approach offers several advantages. No geometric assumptions about ventricular shape are made. All images are acquired from a single point (or window), and the digitized points can be used to make a three-dimensional reconstruction of the ventricle. Also, during the calculations a volume distribution curve for the ventricle is produced. The shape of this curve can be characteristic for certain situations (ie, right ventricle, short axis) and can be used to make new simple equations for calculating volume. We conclude that this is an accurate nongeometric method for determining both right and left ventricular volumes in vitro.

Silent ischaemia following myocardial infarction: frequency, characteristics and prognosis.

Pre-discharge exercise tests were performed in 359 survivors of an acute myocardial infarction to determine the frequency, characteristics and prognostic implications of silent ischaemia. Tests were negative in 152 patients (42%), silent ischaemia was observed in 103 (29%) and painful ischaemia in 82 (23%). Heart rates at the development of ischaemia and the final double products were similar in both ischaemic groups but patients with silent ischaemia were able to exercise for longer (13.1 +/- 0.5 min) than those with painful ischaemia (9.3 +/- 0.5 min; P less than 0.0001). The 12 month mortality rose from 2% in patients with a negative test, to 4% in those with silent ischaemia and to 8% in those with painful ischaemia. Re-infarction rates increased similarly across the groups (3%, 8% and 18% respectively). Patients with silent ischaemia subsequently developed angina more frequently (47%) than those with negative tests (16%; P less than 0.001). These results suggest that exercise-induced silent ischaemia following myocardial infarction was common, occurring in 29% of patients. Although the final myocardial oxygen consumption was similar in both ischaemic groups those with silent ischaemia were able to exercise for longer. Finally silent ischaemia conferred an intermediate risk of death or re-infarction and was a strong predictor of subsequent angina pectoris.

Severity of coronary artery disease and basal fibrinolysis.

Basal venous blood levels of several components of the fibrinolytic enzyme system (plasminogen activator, plasminogen, fibrin degradation products, alpha 2-antiplasmin, and alpha 2-macroglobulin) were measured in 100 white men with angiographically defined coronary artery disease. The tests of fibrinolysis were not related to the severity of coronary artery disease, as indicated either by the number of vessels involved or by a coronary score system. Fibrinogen levels, however, did show a modest association with the extent of coronary atheroma (r = 0.21, p less than 0.05). Triglyceride levels were associated with the inhibitors of fibrinolysis: positively with alpha 2-antiplasmin (r = 0.31, p less than 0.005) and negatively with alpha 2-macroglobulin (r = -0.25, p less than 0.05). The alpha 2-antiplasmin levels were significantly elevated in patients with hypertriglyceridaemia. Neither smoking nor beta-blockade had any effect on the tests of fibrinolysis. This study adds support to the association of plasma fibrinogen with ischaemic heart disease.

Effect of combined nitroglycerin and dobutamine infusion in left ventricular dysfunction.

The immediate therapy of severe left ventricular (LV) failure after acute myocardial infarction (AMI) frequently requires simultaneous preload reduction, pump output augmentation, and maintenance of systemic blood pressure. Therefore the effects of intravenous nitroglycerin (NG) and dobutamine (DB) were evaluated in 12 patients with severe LV failure following AMI. Nitroglycerin achieved salutary lowering of abnormally elevated LV filling pressure (23 to 14 mm Hg, p less than 0.001) while DB markedly augmented LV pump function (cardiac index rose from 1.7 to 2.5 L/min/m2, p less than 0.005). Notably, the combined infusion of NG + DB simultaneously decreased preload (LV filling pressure 23 to 14 mm Hg, p less than 0.001) and markedly enhanced LV pump performance (cardiac index increased from 1.7 to 2.4 L/min/m2, p less than 0.001). Minor decline in mean systemic blood pressure with NG (72 to 66 mm Hg, p less than 0.05) was rapidly reversed by DB addition (69 mm Hg, p greater than 0.05). Both agents were well tolerated without clinical or ECG evidence of myocardial ischemia or dysrhythmias. Thus the principally venodilator effects of NG minimize systemic hypotension while salutary augmentation of cardiac function in AMI with LV failure is achieved by NG + DB.

Simplified right ventricular volume algorithm using one digitized view and transducer tilt angle.

We recently described a technique for determining in-vitro right ventricular volume from multiple two-dimensional echocardiographic views taken at sequential angles. The product of sectional area and center of mass for each view (U) is integrated over the angle of tilt of the transducer to give volume. We now note that the plot of U vs. angle is almost triangular when the echoes are taken from the short axis position. The maximal U value (the vertex of the triangle) and the total angle span (the base) are then used in the equation (maximal U x total angle span)/2 to calculate volume. This new approximation provides an excellent correlation with actual volumes. We conclude that the triangular approximation provides accurate in-vitro estimates of right ventricular volume in normal human hearts.

Cardiocirculatory and myocardial energetic effects of prostaglandin E1 in severe left ventricular failure due to chronic coronary heart disease.

The cardiocirculatory actions of brief (69 +/- 5 minutes) infusions of prostaglandin E1 were evaluated in nine chronic coronary heart disease patients with severe left ventricular (LV) failure caused by previous myocardial infarction. Prostaglandin E1 infusion did not alter heart rate (HR) and produced modest declines in mean systemic blood pressure (BP) (85 +/- 6 to 76 +/- 5 mm Hg, P less than 0.025) and LV filling pressure (19 +/- 3 to 15 +/- 2 mm Hg, P less than 0.01). Simultaneously, prostaglandin E1 augmented LV pump function raising cardiac index from 1.9 +/- 0.2 to 2.5 +/- 0.1 L/min/m2 (p less than 0.005), elevating stroke index from 28 +/- 2.4 to 35 +/- 2.9 ml/beat/m2 (p less than 0.01), and increasing stroke work index from 26 +/- 4.3 to 30 +/- 4.4 gm . m/m2 (p less than 0.02). Additionally, total systemic vascular resistance decreased from 1862 +/- 192 to 1282 +/- 100 dynes-sec-cm-5 (p less than 0.02) and double product LV aerobic index of HR . systolic BP diminished from 9492 +/- 666 to 8278 +/- 492 (p less than 0.02). Concomitantly, in the forearm, vascular resistance fell, blood flow rose, and venous tone remained unchanged. These results indicate that prostaglandin E1 is a potent systemic arteriolar dilator with markedly beneficial effects on cardiac function in chronic coronary patients having severe ischemic LV failure refractory to conventional therapy.

Importance of neuroendocrine regulators of vascular tone and integral adrenoreceptor interaction during oral vasodilator therapy of severe congestive heart failure with prazosin.

The cardiocirculatory actions of the oral vasodilator prazosin were evaluated by cardiac catheterization, forearm plethysmography, echocardiography, treadmill exercise, and symptoms in patients with advanced long-standing congestive heart failure. The administration of oral prazosin (2-7mg) reduced forearm venous tone and forearm vascular resistance. Concomitantly, mean systemic arterial pressure and left ventricular filling pressure decreased, and the cardiac index increased. These effects of a single dose of prazosin on left ventricular function were rapid in onset, maximal at 1 h, and sustained for the entire 6-h period of observation. After 2 weeks of outpatient therapy with 2-7 mg of prazosin four times daily, echographic end-diastolic dimension decreased, whereas the duration of treadmill exercise increased. Symptoms (dyspnea, fatigue, angina) were diminished throughout the course of prazosin therapy, and there was an improvement in the New York Heart Association functional class from 3.7 to 2.2. Thus, prazosin possesses sustained nitroprusside-like balanced dilator actions on the systemic arterial and venous beds, which are effectively translated into the beneficial hemodynamic effects of augmenting cardiac output and relieving excessive left ventricular end-diastolic pressure. The delayed vasodilator tolerance that occurs in 30% of the patients is prevented by the prior use of aldosterone antagonists, and is easily treated when present. Subacute hemodynamic suppression of beneficial prazosin vasodilator actions is transient and does not preclude successful sustained prazosin therapy of severe heart failure.