OBJECTIVE To assess the hydrodynamic properties of three new types of hydrocephalus valve. METHODS Three new constructions have been recently tested in the UK shunt Evaluation Laboratory: the magnetically adjustable Strata Valve (Medtronic PS Medical), the gravitational Miethke Dual-Switch Valve (Aesculap) and the ventriculo-sinus SinuShunt (CSF Dynamics). Pressure-flow performance curves wer...

This study presents a basic idea for the self·excitation mechanism of reed valves in refrigerant compressors used for air conditioners or refrigera· tors. The detailed experimental data on the phase lag of fluid pressure, which were obtained from a forced vibration test on a simple axisymmetrical model, namely a resonator, composed of the valve, the valve plate, the cylinder and the piston, wer...

BACKGROUND AND AIM OF STUDY Pressure gradients across cardiac valve prostheses have been identified as one of the most important performance measures in valve replacement surgery. Specifically in aortic valves, these gradients influence reduction of left ventricular hypertrophy and are postulated to influence long-term survival. The correct choice of replacement valve is hampered by a lack of u...

Volker Weispfenning and his group in Passau have had a long interest in computer algebra. In this talk, REDUCE, one of the algebra programs they use, will be discussed. The development of this program began over forty years ago. We shall discuss the design decisions that have influenced its long-term survival, and the way in which the program has evolved with time.

This paper presents a detailed model of a novel electropneumatic valve actuator for both engine intake and exhaust valves. The valve actuator’s main function is to provide variable valve timing and variable lift capabilities in an internal combustion engine. The pneumatic actuation is used to open the valve and the hydraulic latch mechanism is used to hold the valve open and to reduce valve sea...

BACKGROUND The aim of this study was to investigate the incidence and immediate and mid-term effects of heart valve prosthesis-patient mismatch (PPM) after mitral valve replacement using the GK bileaflet mechanical valve. MATERIAL AND METHODS A total of 493 cases of mechanical mitral valve replacement were performed in the departments of cardiac surgery in 7 hospitals from January 2000 to Jan...

AIMS Hypertension is a frequent finding in patients with aortic stenosis (AS). However, controversial data about the influence of systemic blood pressure on the quantification of AS have been published. METHODS AND RESULTS Various models of AS (plates and biological valves) were studied in an in vitro circuit. Valve areas were calculated with the Doppler continuity equation and the Gorlin for...

A better course of the disease after implantation of a low-pressure valve in patients with idiopathic normal pressure hydrocephalus normally comes at the cost of a distinctly higher rate of overdrainage. Can combining an adjustable valve with a gravity unit produce optimization of treatment results? In a prospective observation of the course of the disease, 18 patients with idiopathic normal pr...

The lung was biopsied in 20 children with double inlet ventricle and pulmonary hypertension aged 2 months to 14 years. Eleven patients had two patent atrioventricular valves, three atresia of the right valve, and six hypoplasia of the left valve. Severe pulmonary arterial medial hypertrophy occurred in the nine children less than 1 year of age. The findings did not suggest a period of normality...