Kinetics of nitrite reduction by zinc metal: influence of metal shape on the determination of kinetic parameters.

Heterogeneous chemical reactions are complicated, especially in the case of competitive reactions. The aim of this study was to investigate the elimination of nitrite (NO2(-)) by applying a metallic reduction using zero-valent zinc (Zn0). The effect of pH, stirring, and metal shape (powder and chips) on the rate and products of nitrite reduction were studied in a batch-stirred reactor. The obtained data have been used to optimize the conditions for metallic reduction of NO2(-) and for kinetic parameters identification. It was found that the dissolution of zinc involves a pseudo-first-order reaction independent of the shape of the metal. Further, the influence of operating conditions on nitrogen (N2) and ammonium (NH4(+)) formation has been determined. It was found that a decrease in pH and in the Zn0 content enhances NH4(+) production. If kinetic parameters can be approximated easily for constant surface area, it was demonstrated that surface evolution had to be integrated for metal powder. Finally, a numerical simulation has been used to determine the kinetic parameters for NO2(-) reduction with zinc powder.

Antihypertensive treatment in elderly hypertensives without a history of stroke and the risk of cognitive disorders.

OBJECTIVES: The role of the antihypertensive therapy in preventing cognitive disorders in elderly persons without a history of stroke is a matter of debate. This review focuses on the pathogenesis of the cognitive disorders in elderly hypertensives and on the risk factors of their occurrence. METHODS: Relevant papers were identified by searches in PubMed from 1946 until October 2007, using the key words 'vascular risk factors', 'vascular cognitive impairment', 'vascular dementia', 'neuroimaging in hypertension' and 'antihypertensive treatment'. RESULTS: Blood pressure lowering in elderly patients with long-standing hypertension below a certain critical level may increase the risk of cerebral hypoperfusion and cognitive decline, particularly in cases with additional vascular risk factors. Cerebral white matter lesions have been found in the majority of elderly hypertensives. They have been shown to correlate with cognitive disorders. CONCLUSIONS: Appropriate neuropsychological assessment and follow-up of the cognitive functions could be considered with the aim to individualize the antihypertensive therapy and slow down cognitive decline. Prospective studies are needed to confirm such a treatment strategy.

Monitoring of microbial adhesion and biofilm growth using electrochemical impedancemetry.

Electrochemical impedance spectroscopy was tested to monitor the cell attachment and the biofilm proliferation in order to identify characteristic events induced on the metal surface by Gram-negative (Pseudomonas aeruginosa PAO1) and Gram-positive (Bacillus subtilis) bacteria strains. Electrochemical impedance spectra of AISI 304 electrodes during cell attachment and initial biofilm growth for both strains were obtained. It can be observed that the resistance increases gradually with the culture time and decreases with the biofilm detachment. So, the applicability of electric cell-substrate impedance sensing (ECIS) for studying the attachment and spreading of cells on a metal surface has been demonstrated. The biofilm formation was also characterized by the use of scanning electron microscopy and confocal laser scanning microscopy and COMSTAT image analysis. The electrochemical results roughly agree with the microscope image observations. The ECIS technique used in this study was used for continuous real-time monitoring of the initial bacterial adhesion and the biofilm growth. It provides a simple and non-expensive electrochemical method for in vitro assessment of the presence of biofilms on metal surfaces.

Multiple modifiable risk factors for first ischemic stroke: a population-based epidemiological study.

The aims of this epidemiological population-based cohort study were to examine the prevalence of the multiple modifiable vascular risk factors, their distribution patterns and outcomes among a Bulgarian urban population. A total of 500 volunteers, 200 men and 300 women, without clinical signs and symptoms of cerebrovascular disease, aged 50-79 years, were enrolled in the study. A structured questionnaire, physical examination, electrocardiogram records, a battery of laboratory tests and carotid duplex scanning were employed. Three or more modifiable vascular risk factors were detected in 52% (260/500) of the subjects. Dyslipidemias, hypertension, obesity, cigarette smoking and cardiac diseases were found to be the most prevalent single risk factors. Asymptomatic carotid stenosis (ACS) of 50% or greater was detected in 8.8% (23/260) of the volunteers examined. After a 2-year follow-up, 2.7% (7/260) of the persons with modifiable vascular risk factors reached the end point transient ischemic attacks (TIAs), ischemic stroke and myocardial infarction. The following combinations of risk factors among the subjects enrolled in the study were significantly associated with these outcomes: hypertension and cardiac diseases (OR = 6.82; 95% CI, 1.21-38.41), cardiac diseases and obesity (OR = 6.13; 95% CI, 1.27-29.72), ACS and high low-density lipoprotein (LDL) cholesterol levels (OR = 11.11; 95% CI, 1.58-78.29). The identification of subjects with multiple vascular risk factors may be important for primary medical or surgical stroke prevention.

Prevalence and outcome of asymptomatic carotid stenosis: a population-based ultrasonographic study.

The aims of this epidemiological population-based cohort study were to examine the prevalence and outcomes of asymptomatic carotid stenosis (ACS) detected by duplex scanning and its relations to other vascular risk factors. A total of 500 volunteers, 200 men and 300 women, without signs and symptoms of cerebrovascular disease, aged 50-79 years, were enrolled in the study. The prevalence of ACS of 50% or greater was 6.4%. Only severe carotid stenosis was detected in 0.4% of the subjects examined. Significant relationships between ACS and coronary heart disease (CHD) [odds ratio (OR)=8.00], peripheral arterial disease (PAD) (OR=3.66), cigarette smoking in men (OR=4.39) and obesity in women (OR=0.31) were found. The biennial incidence rate of cerebral ischaemic events was 9.4%. A progression of ACS was revealed in 14% and a regression in 6.25% of the subjects. The patients with progressing ACS to more than 70% diameter reduction reached the end-points. Follow-up with repeated duplex scans in patients with advancing ACS of 50% or greater, especially smokers with CHD and PAD, is recommended.

Prevalence of stroke risk factors and their outcomes. A population-based longitudinal epidemiological study.

This epidemiological study was performed to determine the prevalence of stroke risk factors and their outcomes among Bulgarian urban population. Volunteers, 200 men and 300 women, aged 50-79 years, without clinical signs and symptoms of vascular disease were enrolled in the study. A structured questionnaire, physical examination, ECG records and a battery of laboratory tests were employed. All volunteers underwent a carotid Duplex scan. High LDL-cholesterol levels, hypertension, obesity, cigarette smoking and cardiac diseases were the most prevalent risk factors. The annual incidence rate for TIA was 0.96% and for ischemic stroke -0.72%. Myocardial infarction incidence rate was 0.48%. Asymptomatic carotid stenosis (ACS) of 50% or greater was significantly related to the cerebral ischemic events (OR: 4.74; 95% CI 1.24-18.16). The aggregation of ACS and alcohol abuse was also significantly associated with cerebral ischemic events (OR: 5.04; 95% CI 1.29-19.63).

Cerebral blood flow autoregulation during orthostatic manoeuvre in patients with permanent cardiac pacemaker.

Orthostatic test with passive tilting of the upper body was performed in 28 patients with VVI pacemaker. The changes in BP (Riva-Rocci method), CVR and CBF (impedance technique, REG II) as well as in EEG (automatic spectral analysis) observed after tilting, were compared to those in 20 age-matched controls. While in healthy subjects the autoregulation of the CBF was accomplished through a decrease in CVR and resulted in a moderate but significant increase in CBF, in patients the CVR did not change. This event was estimated as a sign of impaired autoregulation, the CBF remained unchanged most probably on account of the increased diastolic and mean BP. Alpha and beta power spectra in the EEG rose significantly after tilting, the shifts being more pronounced in the controls. In the patients there was an increase in theta activity. Cerebral angiopathy due to "subclinical" brain ischaemia during cardiac rhythm disorders preceding pacemaker implantation was accepted as a mechanism underlying the disturbed autoregulation of the cerebral blood flow. For the occurrence of alterations in orthostatic EEG reactivity, a dyscirculatory encephalopathy has been suspected.

Nimodipine in the treatment of headache in chronic cerebral ischemia.

The aim of this study was to evaluate the influence of nimodipine on non-migrainous vascular headache in patients with chronic cerebral ischemia. Eighty-six patients were examined in a double-blind trial for 16 weeks (12 weeks of nimodipine or placebo, followed by a 4-week placebo period). Fifty-six patients were studied in an open trial for 12 months. In the total material of the double-blind study there was no difference as far as improvement of headache was concerned when comparing the patients treated with nimodipine with those receiving placebo. However, in a group of 38 patients with a higher degree of headache intensity, selected in accordance with the Sandoz Clinical Assessment Geriatric scale, a statistically significant difference was found in favor of nimodipine. The results obtained in the long-term open trial seem to confirm the effect of nimodipine on headache. The underlying mechanisms of the beneficial effect of the drug have been discussed.

Effect of aligeron on the cerebral venous outflow and cerebrospinal fluid pressure in dogs.

The effect of Aligeron (1-benzhydril-4-allyl-piperazine dihydrochloride) on the cranial circulation was studied in dogs under chloralose-urethan anaesthesia. The parameters followed were: venous outflow from the confluence of the cerebral sinusses (CVO), cerebrospinal fluid pressure in cysterna magna (CSFP), systemic arterial blood pressure (BP) and pulse rate (PR). CVP was measured using the technique of Rapela and Green (1964). Aligeron was applied at doses of 5 and 10 mg/kg i.v. Papaverine hydrochloride was used as a reference compound. aligeron administration at a dose of 5 mg/kg led to quick increase of the CVO with a duration of the effect approximately 30 min. CSFP also increased in a similar way. BP and PR showed insignificant changes. The administration of 10 mg/kg did not lead to an increase of its effect on CVO. Papaverine (1 mg/kg i.v.) had a weaker effect than that of Aligeron. According to the classical concepts the changes observed in our experiments were due to the cerebral vasodilator effect of Aligeron which caused a fall in cerebrovascular resistance and an increase of the intracranial blood volume. Our experiments suggest that Aligeron influenced the resistance vessels more than the capacitance ones.

Rheoencephalographic and psychological studies with ethyl apovincaminate in cerebral vascular insufficiency.

The effect of ethyl apovincaminate (RGH-4405, Cavinton) on the rheoencephalogram and memory functions was studied in 50 patients with ischaemic disturbances of cerebral circulation. The drug was administered in a single i.v. dose of 10 mg and orally three times daily 5 mg for a month. Improvement of cerebral circulation was observed after i.v. and oral medication. Blood flow was most markedly increased in the gray matter. The effect on arterial pressure was negligible. Improvement of memorizing capacity evaluated by psychological tests was recorded after one month of Cavinton treatment, associated with alleviation or complete disappearance of symptoms. No side-effects attributable to the drug were observed. It is pointed out that Cavinton is indicated in the treatment of ischaemic disorders of the cerebral circulation, particularly in chronic insufficiency.