On Stress Reduction in Bioprosthetic Heart Valve Leaflets by the Use of a Flexible Stent

It has been postulated that flexible stent posts can reduce tensile stress at the commissures of tissue heart valves by about 90% when compared with the same valve mounted on a rigid stent. We have used a detailed computer model to investigate the role of flexible stent posts in reducing stress in the leaflets of three types of bioprosthetic heart valves: the bovine pericardial and the high- and zero-pressure fixed porcine valves. The models use stress/strain data from biaxial experiments to characterize the tissue properties and are subjected to a back pressure of 120 mmHg. We found that strain was reduced linearly with stent post deflection and that this was a purely static process--it did not require the load to be applied impulsively. This finding was in close agreement with earlier experimental studies, which measured the same strain reduction whether the valve was loaded quasi-statically or at physiological rates. In addition, we found that for this mechanism to be effective the valve must have good coaptation at the center and the tissue should be stiff; in other cases, the advantages of strain reduction through the use of a flexible stent are considerably diminished.     

Pacemaker Failure Induced by Radiotherapy

It is well documented that radiation therapy can have significant transitory and permanent effects on the function of cardiac pacemakers. In this study 18 multiprogrammable pacemakers were tested to establish any pattern by which these pacemakers are affected. The results confirm previous predictions on how pacemakers are damaged. The damage could be divided essentially into three types: (1) temporary change to interference or safety mode pacing lasting for the duration of the irradiation only; (2) change to interference mode pacing—from which recovery may occur after reprogramming the pacemaker; and (3) severe damage; in this case the pacemaker stops generating pulses. Recovery from this may occur a long time after the end of the treatment, but this recovery is mostly incomplete and the pacemaker cannot be used reliably thereafter. Therefore it is essential that patients with implanted pacemakers undergoing radiation therapy, should be monitored closely during the course of the treatment and for a few weeks thereafter.     

The use of video image analysis for the measurement of venous ulcers

Summary The accurate measurement of the size of skin wounds and ulceration is important for comparing the efficiency of treatment modalities and for monitoring progress in the individual patient. Although various methods of differing sophistication are in use, many of the common simpler techniques lack accuracy and reliability.
We describe a new technique of ulcer measurement which uses video image recording, capture and computer analysis. A method of correcting for limb convexity in a two-dimensional image is presented. The method has an overall accuracy of 1–82% and a clinical precision of 3–41%, both of which are significantly better than acetate tracings or photographic methods. The technique is simple and rapid, and once established it incurs minimal ongoing costs.