Computational studies of 'whiplash' injuries.

The term 'whiplash' was initially used to describe injuries to the neck caused by the head being forced backwards during a rear-end collision in cars without head restraints. The addition of head restraints in the 1970s was expected to solve this problem by preventing excessive extension of the neck but experience suggests the problem still exists. This paper reviews available experimental studies of whiplash and uses the data to construct a finite element model which is capable of dynamically simulating whiplash collisions and predicting the forces in all the relevant neck ligaments. For the first time, it is shown that trauma occurs long before the head hits the head restraint as a result of displacement between the head and the torso caused by the head's inertia leading to markedly different acceleration histories. It is concluded that experimental and computational studies must be used together to produce progress in biomechanical studies.

Conduit-mounted cardiac valve prostheses: a review of their uses, design and in vivo performance.

Although providing an historical overview of the development and clinical applications of conduit-mounted prosthetic heart valves, with elementary explanations of operative techniques, this review concentrates on the impact of design and surgical considerations on their in vivo performance. Areas showing potential for design improvement of mechanical prostheses are highlighted, both in terms of haemodynamic efficiency and haemocompatibility. Comparisons are drawn throughout the paper with conventional valve prostheses, and the key features where they differ significantly are pointed out. It is concluded that there is considerable scope for further worthwhile development.

A review of the in vitro evaluation of conduit-mounted cardiac valve prostheses.

This review concerns the issues affecting the in vitro evaluation of conduit-mounted prosthetic heart valves at the design development stage, and the question of standardisation of testing at the quality assurance stage. Particular attention is given to areas of conduit valve development and research which have been neglected, ambiguously covered or left to the discretion of the researcher in the current standard for conventional prosthetic valves, ISO 5840.

Development of a ceramic conduit valve prosthesis for corrective cardiovascular surgery.

This paper reports some of the ways in which biomaterial considerations have influenced the design, development and construction methods for a prototype conduit valve prosthesis in which the valve body is made from alumina. This material is used principally for its ability to grow and support a thin (< 0.1 mm) tissue covering on the surfaces in contact with the blood. This non-vascular covering does not interfere with the operation of the valve, but is thick enough to camouflage the underlying surface from any further interaction with the blood. This is important for any conduit valve because of the large internal surface area, but would be especially beneficial for children if it could obviate the need for chronic anticoagulation.

Mammobarography: a possible method of mass breast screening.

Preliminary details are given of a novel method of detecting breast lumps. The technique relies on the fact that such a lump will cause a perturbation in the pressure distribution when the breast is loaded against a flat plate. The pressure distribution is monitored by using the principle of frustrated total internal reflection to generate a brightness distribution which can then be presented as a contour map in synthesized colour. Using this technique, simulated lumps in breast prostheses have been detected down to a diameter of 6 mm. It is argued that this represents the basis of a method of mass breast screening.

Theoretical evaluation of energy loss methods in the analysis of prosthetic heart valves.

The purpose of this paper is to clarify certain aspects of the 'energy loss' approach to the analysis of artificial heart valves. This involves the discussion of what is meant by 'energy loss'; the derivation of an appropriate energy equation; the scrutiny of the conditions under which it may be applied and of the assumptions involved in deriving a useful formulation in terms of readily measurable parameters; consideration of the extent to which these assumptions are valid in reported experiments using this formulation and the demonstration of the suitability and versatility of this approach when applied specifically to heart valve conduits.

Minimization of pressure drop across heart valve conduits: a preliminary study.

Commercially available valved conduits are subject to large pressure drops in forward flow which can limit the exercise capability of recipients. However, there is considerable scope for improvement compared with valves which are mounted inside the heart, because there are fewer restrictions on flow guidance due to the constraints of size and sewing rings. Accordingly three model conduits have been tested in steady flow using a rigid body and a ball occluder. The best one is shown to have a pressure drop many times lower than a commercial conduit and several times lower than even a healthy natural valve of the same diameter. It would therefore offer a significant improvement if it could be made of a suitable material.

Development of a twin-flap, porous ceramic mitral valve prosthesis.

The pressure drop in most existing cardiac valve prostheses is at least ten times greater than for healthy valves. Steady flow testing indicates that the causes are (i) poor orifice diameter/sewing ring diameter ratio; (ii) occluding mechanism causes obstruction in the region of highest blood velocity. A new mitral prosthesis was constructed to overcome these deficiencies. The significant features are (a) tubular construction to maximize flow area; (b) twin flaps with hinges well above the outlet to minimize obstruction; (c) divergent nozzle to aid pressure recovery. Prostheses were manufactured from porous alumina, promoting firmly anchored, thin tissue growth to reduce haemolysis and thromboembolism. Preliminary trials in mini-pigs show good valve function. The ceramic behaves especially well. Future models will use ceramic flaps to replace the delrin flaps used ast present, which encourage fibrin deposits.