Rate-dependent and antiarrhythmic reentrant tachycardia (AVNRT) effects of simvastatin in isolated rabbit atrioventricular nodal model

Background and purpose: Several previous studies have shown the direct and indirect effects of statins on supraventricular and ventricular arrhythmia. The purpose of the present study is to determine (1) whether Simvastatin modifies the rate-dependent properties of the AV node, (2) to what extent such changes are related to effect of Simvastatin on the basic properties of AV nodal conduction and refractoriness. Materials and methods: AV nodal refractoriness (AVERP & AVFRP) and rate dependency protocols Fatigue and Facilitation were used to assesse the electrophysiological properties of AV node. We used an isolated perfussed rabbit with AV nodal preparation in one group (N=8). The stimulation protocols were carried out during control phase and in the presence of various concentrations of Simvastatin (0.5 , 0.8 , 1, 3 ,10 μm). Results: Simvastatin in concentration-dependent manner successfully prolonged effective and functional nodal refractory period (AVERP & AVFRP). Also an increase in Wenckebach cycle length was observed. Simvastatin in high concentration (3,10 μm) increases the arrhythmia threshold. Various concentrations of simvastatin increased fatigue, but it reached to significant level only at 30 μM. Conclusion: Simvastatin has potential anti-AVNRT effects by elevating arrhythmia threshold and prolongation of nodal refractoriness

Stress among medical students of Gorgan (South East of Caspian Sea), Iran

Objective: This study aims to estimate the prevalence of psychological stress and association between the levels of stress and study variables among Gorgan medical students. Materials and methods: All three year medical students (129 basic sciences students) in Gorgan Faculty of Medicine, Golestan University of medical Sciences, were asked to complete the Kessler 10 questionnaire. Results: The findings showed mild, moderate and severe stress among 26.22%, 20.50% and 14.75% study subjects. 39.35% of medical students had no stress. There was statistically significant association between year of study and stress levels (p= 0.040). Conclusion: The results indicate that there is a decrease in the psychological health of first year medical students. Provided that stress management courses are organised by medical schools, when the students arrive, they will cope up with the stress in coming years. These courses may reduce the negative effects of stress on medical students. By providing such courses and reducing stress level, medical students may improve their medical education

The Kumaraswamy Marshal-Olkin Family of Distributions

We introduce a new family of continuous distributions called the Kumaraswamy Marshal-Olkin generalized family of distributions. We study some mathematical properties of this family. Its density function is symmetrical, left-skewed, right-skewed and reversed-J shaped, and has constant, increasing, decreasing, upside-down bathtub, bathtub and S-shaped hazard rate. We present some special models and investigate the asymptotics and shapes of the family. We derive a power series for the quantile function and obtain explicit expressions for the moments, generating function, mean deviations, two types of entropies and order statistics. Some useful characterizations of the family are also proposed. The method of maximum likelihood is used to estimate the model parameters. We illustrate the importance of the family by means of two applications to real data sets

A New Weibull-G Family of Distributions

Statistical analysis of lifetime data is an important topic in reliability engineering, biomedical and social sciences and others. We introduce a new generator based on the Weibull random variable called the new Weibull-G family. We study some of its mathematical properties. Its density function can be symmetrical, left-skewed, right-skewed, bathtub and reversed-J shaped, and has increasing, decreasing, bathtub, upside-down bathtub, J, reversed-J and S shaped hazard rates. Some special models are presented. We obtain explicit expressions for the ordinary and incomplete moments, quantile and generating functions, Renyi entropy, order statistics and reliability. Three useful characterizations based on truncated moments are also proposed for the new family. The method of maximum likelihood is used to estimate the model parameters. We illustrate the importance of the family by means of two applications to real data sets