Silica nanoparticle monolayers on a macroion modified surface: formation mechanism and stability.

Even though silica nanoparticles and their monolayers find a broad field of applications, only a few studies providing a quantitative description of silica nanoparticle deposition at solid/liquid interfaces have been reported in the literature. Given the deficit of reliable experimental data, the goal of this work is to acquire thorough physicochemical characteristics of amorphous silica nanoparticle deposition. Silica nanoparticle monolayers of controlled coverage were formed on macroion (PAH)-modified mica. The size of the particles determined by dynamic light scattering (DLS), atomic force microscopy (AFM) and scanning electron microscopy (SEM) was equal to 28 nm. The electrophoretic mobility and the zeta potential of the particles were also determined as a function of ionic strength and pH. Using a well-defined suspension, systematic studies of particle deposition kinetics were carried out. The coverage of the self-assembled particle monolayers was determined by AFM and SEM imaging. Particle deposition was carried out under diffusion controlled transport conditions. For long deposition times, the saturation coverage was attained, systematically increasing with ionic strength up to 0.48 for I = 0.15 M NaCl. The deposition kinetic runs were adequately interpreted using the random sequential adsorption (RSA) model. This model was also used to determine the specific density of silica particles that confirmed their porous structure. In addition, the particle desorption kinetics was studied using AFM and SEM methods. It was confirmed that silica nanoparticle desorption was negligible within the time period of 60 hours. Our experimental data proved, therefore, that it is feasible to produce uniform and stable silica particle monolayers of desired coverage in the self-assembly processes, controlled by the bulk suspension concentration and the ionic strength. Such monolayers may find practical applications as substrates for selective protein and nanoparticle deposition, or various catalytic applications.

Formation and influence of the dynamic adsorption layer on kinetics of the rising bubble collisions with solution/gas and solution/solid interfaces.

BACKGROUND: The DAL (dynamic adsorption layer) formation, that is, the establishment of uneven distribution of adsorption coverage over the rising bubble surface, with significantly diminished coverage at the upstream pole, is the factor of crucial importance for the bubble motion parameters and kinetic of the bubble collisions with various interfaces. The DAL presence can influence the stability of the thin liquid films formed by the colliding bubble at solution/gas and solution solid interfaces. AIM: The purpose of this paper is to critically review the existing state of art regarding the influence of the DAL formation and existence on the bubble motion parameters as well as kinetics of coalescence at free solution surface and three phase contact (TPC) formation at solid/liquid interfaces of different hydrophilic/hydrophobic properties. CONCLUSIONS: Despite the fact that up to now there is no direct experimental evidence showing DAL existence, it is documented by experimental data showing clear correlation between bubble local velocity variations and shape pulsations as well as lifetimes of the liquid film formed by the colliding bubble at gas/liquid and gas/solid interfaces.

Efficacy of sequential antiarrhythmic treatment in sinus rhythm maintenance after successful electrocardioversion in patients with chronic non-valvular atrial fibrillation.

BACKGROUND: Sequential use of antiarrhythmic drugs may improve prognosis in chronic atrial fibrillation (AF). We conducted a prospective study of the efficacy of sequential antiarrhythmic drug therapy in sinus rhythm (SR) maintenance after a successful electrocardioversion (CV) in pts with chronic AF. MATERIAL AND METHODS: 58 pts (64.3 +/- 4.3 years old) with chronic AF underwent CV. After SR restoration (Group I) pts received one of the following antiarrhythmic drugs (Drug I): propafenone, sotalol or disopyramide. In case of arrhythmia recurrence, second CV was performed and pts received another drug from those mentioned above (Drug II). If treatment proved to be unsuccessful pts received amiodarone (Drug III) and third CV was attempted. After first unsuccessful CV (Group II) pts received a loading dose of amiodarone and another CV was attempted. In case of SR restoration amiodarone was administered continuously. RESULTS: After 12 months 81% pts were on SR; 85% pts received amiodarone continuously. After 1 year 6 (10%) pts presented with SR treated with Drug I (median 71 days); Drug II proved to be ineffective in all patients (median 27 days). 28 pts continued to receive amiodarone (no median). CONCLUSIONS: Sequential antiarrhythmic drug therapy improves arrhythmia prognosis in AF within a 12-month observation period. Amiodarone seems to be the most effective antiarrhythmic drug also in pts who required second CV proceeded by amiodarone treatment to restore SR.

[Effect of postinfarct left ventricular dysfunction on late occurrence of mitral regurgitation--two year experience]. / Wplyw pozawalowego uszkodzenia lewej komory na wystepowanie póznej niedomykalnosci mitralnej--obserwacja 2-letnia.

The aim of this study was to evaluate factors that might influence on the occurrence of mitral regurgitation (MR) in patients (pts) following myocardial infarction (MI) after fibrinolysis--two year experience. The study group comprised 118 pts: 40 women and 78 men (mean age: 58 +/- 9 years) following MI, who underwent Doppler echocardiography which revealed no MR 3 weeks after the MI. The second echocardiographic examination was performed after 2 years. We evaluated the following parameters: presence and stage of MR, left ventricular end-diastolic diameter (LVDD), left atrial diameter (LA), end-diastolic volume (EDV), wall motion score index (WMSI), asynergic area (AA) and ejection fraction (EF). Results after 2 years were as follows: 43 pts (36%) presented without MR, 45 (38%) MR I degree, 27 (23%) MR II degree, 3 (3%) MR III degree. Echocardiographic parameter comparison after 2 years demonstrated the following changes: LVDD increase from 5.0 +/- 0.5 cm to 5.3 +/- 4.6 cm (p < 0.005), LA increase from 3.7 +/- 0.4 cm to 4.3 +/- 0.4 cm (p < 0.00001), EDV increase from 130 +/- 29 ml to 147 +/- 39 ml (p < 0.005), WMSI increase from 1.37 +/- 0.23 to 1.45 +/- 0.21 (p < 0.05), AA increase from 23.5 +/- 10.1% to 27.8 +/- 7.9% (p < 0.005) and significant EF decrease 50.4 +/- 7.9% to 46.9 +/- 7.1% (p < 0.005). These results demonstrate that the occurrence of MR 2 years after the MI is caused by left ventricular remodelling, as well as segmental and global function deterioration.

Paroxysmal atrial fibrillation in a young female patient following marijuana intoxication--a case report of possible association.

Marijuana is one of the most popular drugs legally admitted for general sale in many countries. To consider it safe and unlikely to develop drug dependence is abusive. The use of marijuana as a herbal medication is being widely discussed in literature. The most promising effect of delta-9-etrahydrocannabinol seems to be observed in the case of nausea, following cancer chemotherapy. Despite its positive action on the human organism, marijuana smoking has been shown to exert adverse effects on the cardiovascular system causing well-tolerated tachycardia and/or hypotension. We also observed that marijuana abuse was associated with an increased risk of paroxysmal atrial fibrillation. The report presents a case of young healthy white subject suffering from paroxysmal atrial fibrillation following marijuana intoxication. The abuse of this substance was the most possible and identifiable risk factor for observed paroxysmal atrial fibrillation.

An increase in plasma atrial natriuretic peptide concentration during exercise predicts a successful cardioversion and maintenance of sinus rhythm in patients with chronic atrial fibrillation.

The aim of this study was to determine the value of an increase in plasma atrial natriuretic peptide (ANP) concentrations during submaximal exercise as a predictor of return of sinus rhythm (SR), and of its maintenance over a period of 6 months after cardioversion (CV) of chronic atrial fibrillation (AF). The study group included 42 patients with AF (mean duration 7 +/- 7 months) and a controlled ventricular rate. They underwent submaximal exercise testing 24 hours before CV. Blood samples were collected at rest and at peak of exercise for measurement of plasma ANP concentrations. Thirty-five of 42 patients were successfully cardioverted to SR. At 6 months, 23 patients remained in SR, while 12 had recurrence of AF. The plasma ANP concentrations before CV increased insignificantly during exercise in patients with unsuccessful CV or with recurrence of AF (60.8 +/- 17.3 pg/mL to 64 +/- 13.5 pg/mL, NS). The mean increase in plasma ANP concentration during exercise was significantly greater in the 23 patients who remained in SR than in the 19 patients unsuccessfully cardioverted or with recurrence of AF (17.5 +/- 7.6 pg/mL vs 5.8 +/- 4.5 pg/mL, P < 0.01). In multivariate logistic regression analysis, an increase in ANP plasma concentration was independently associated with successful CV and maintenance of SR up to 6 months of observation. In patients with chronic AF an exercise-induced increase in ANP concentration predicts successful CV and maintenance of SR.

[Should sinus rhythm be restored in patients with chronic atrial fibrillation? Preliminary results from the Polish "Hot Cafe" study]. / Czy przywracac rytm zatokowy u chorych z przewleklym migotaniem przedsionków? Wstepne wyniki polskiego badania "Hot Cafe".

Atrial fibrillation (AF) is the most common arrhythmia occurring in clinical practice. It is the most frequent cause of hospitalization in cardiac rhythm disturbance. Despite comprehensive progress in the research into electrophysiological mechanisms leading to this loss of normal rhythm and new procedures dealing with it, the main problem being the conversion to and maintaining the normal sinus rhythm (SR) has not been solved. The polish study "Hot Cafe" is trying to evaluate the advantages and risks of the two procedures widely used in clinical practice in patients (pts) with chronic AF, i.e. conversion and maintaining SR vs leaving pts with the arrhythmia. Pts with non-valvular chronic AF fulfilling the criteria for including them into the sample are randomly assigned to two procedures: conversion to SR by means of direct current cardioversion and maintaining it or leaving pts with AF. Pts left with AF are treated by rate control and antithrombotic treatment. The project is of prospective kind and it will be carried out by many medical institutions. It is planned to include 200 pts. The observation period will last at least 12 months. Preliminary results after inclusion of the first 121 pts are shown.