Left ventricular volume and valve gradient analysis using an Apple Macintosh computer

A description of a computer program to analyse cine angiograms of the heart and pressure waveforms to calculate valve gradients.

pH testing for detecting the position of nasogastric tubes in adults and children (Intervention Protocol)

This is the protocol for a review and there is no abstract. The objectives are as follows: Our objective is to determine if there is sufficient evidence to recommend the use of pH testing (the intervention under scrutiny) for verification of correct placement of nasogastric tubes in adults and children. To this end, we will attempt to answer the following questions: 1. In adults and children, is pH testing an effective and safe method for determining whether nasogastric tubes are correctly positioned in the stomach before feeding (or delivery of any fluid) begins? 2. What evidence is there about the risk of adverse events in the case of incorrect placement? For this review, pH testing is defined as: litmus paper, pH indicator test strips, pH meters. These will be tested against other methods used for detecting placement of nasogastric tubes, including visual examination of aspirate, auscultation with insufflation of air, detection of air bubbles in a bowl of water, X-ray, ultrasonography, endoscopy, enzyme analysis of aspirate, capnography, and other methods that do not rely on measurement of pH.

The mechanical triggers of plaque rupture: Shear stress vs pressure gradient

The aim of this study was to evaluate the mechanical triggers that may cause plaque rupture. Wall shear stress (WSS) and pressure gradient are the direct mechanical forces acting on the plaque in a stenotic artery. Their influence on plaque stability is thought to be controversial. This study used a physiologically realistic, pulsatile flow, two-dimensional, cine phase-contrast MRI sequence in a patient with a 70% carotid stenosis. Instead of considering the full patient-specific carotid bifurcation derived from MRI, only the plaque region has been modelled by means of the idealised flow model. WSS reached a local maximum just distal to the stenosis followed by a negative local minimum. A pressure drop across the stenosis was found which varied significantly during systole and diastole. The ratio of the relative importance of WSS and pressure was assessed and was found to be less than 0.07% for all time phases, even at the throat of the stenosis. In conclusion, although the local high WSS at the stenosis may damage the endothelium and fissure plaque, the magnitude of WSS is small compared with the overall loading on plaque. Therefore, pressure may be the main mechanical trigger for plaque rupture and risk stratification using stress analysis of plaque stability may only need to consider the pressure effect.

Development of a transient gradient enhanced non local continuum damage mechanics model for masonry

Due to the advent of varied types of masonry systems a comprehensive failure mechanism of masonry essential for the understanding of its behaviour is impossible to be determined from experimental testing. As masonry is predominantly used in wall structures a biaxial stress state dominates its failure mechanism. Biaxial testing will therefore be necessary for each type of masonry, which is expensive and time consuming. A computational method would be advantageous; however masonry is complex to model which requires advanced computational modelling methods. This thesis has formulated a damage mechanics inspired modelling method and has shown that the method effectively determines the failure mechanisms and deformation characteristics of masonry under biaxial states of loading.