Circumferential and longitudinal viscoelasticity of human iliac arterial segments in vitro

A random noise technique was used to measure the circumferential and longitudinal dynamic elasticity of human common iliac arteries in vitro. For circumferential measurements the frequency ranged from 0.016 to 20 Hz; the phase lag of diameter behind pressure was found to be almost constant (about 5 degrees) and the Young's modulus of elasticity to increase rapidly at first and then more gradually beyond 1-2 Hz. Somewhat similar results were obtained for longitudinal elasticity. Arterial segments were found to be anisotropic when kept at in vivo length and under normal distending pressure.

Arterial system configuration and wave reflection

On the assumption that the arterial segments between branching points are cylindrical, the relationship between total arterial cross-sectional area and the distance from the heart for the entire length of the arterial system is derived. Based on this relationship, a model of the whole arterial system is proposed; it is composed of three tubes of common origin and of unequal lengths and cross-sectional areas. This model may be useful for simulation purposes, with particular reference to pulse wave reflections.

Physical modelling of the arterial wall. Part 2: Simulation of the non-linear elasticity of the arterial wall

In part 1 it was established that the elasticity of tubes made from natural rubber is, at low pressures, close to that of the arterial wall; in this part a method is described for reinforcing the walls of rubber tubes so that they may be used for simulating arterial elasticity at higher pressures. The technique is versatile in that, within reasonable limits, wall non-linearity can be modified; tubes with non-linear wall elasticity were produced and tested. A modification of the method enabled us to produce geometrically non-uniform rubber tubes which may be useful in the construction of physical models of the arterial system.

Physical modelling of the arterial wall. Part 1: Testing of tubes of various materials

Tubes of various elastic materials were tested using a purpose-built apparatus to select those most appropriate for physical simulation of the arterial wall. The influences of temperature and longitudinal stress were measured in selected tubes. It was found that the static elasticity of latex tubes is close to that of the arterial wall for intraluminal pressures corresponding to the lower range of intra-arterial pressures.

Photoelectric transducer for measuring the length and diameter of elastic vessels

This photoelectric transducer was developed to measure diameter and length variations in arterial segments in vitro and in elastic tubes. Its construction is simple, its nonlinearity small and its sensitivity adequate. The cut-off frequency is 300 Hz and its small phase lag changes linearly with frequency.

A low-cost colorimeter

A need for a colorimeter with low capital and maintenance costs has been suggested for countries with foreign exchange problems and no local medical instrumentation industry. This paper puts forward a design for such a device based on a domestic light-bulb, photographic filters and photovoltaic cells. The principle of the design is the use of a balancing technique involving twin light paths for test solution and reference solution and an electronic bridge circuit. It is shown that proper selection of the components will allow the cost objectives to be met and also provide acceptable linearity, precision, accuracy and repeatability.

A first-degree course in electronics, with medical instrumentation as a background topic

A course is described in which undergraduate students of electronics can study aspects of medical instrumentation throughout a three-year period. This course includes as much electornics as a normal B.Sc programme in Electronics but contains a background theme of medical engineering and bioengineering amounting to 20% of the total work load. The course is compared with two similar courses in Britain and also with courses abroad. Some consideration is given to the educational content of this course as well as to employment opportunities and social trends.

Natural selection and birthweight

Mean birthweight, even before induced births became commonplace, is slightly lower than the birthweight at which perinatal mortality is lowest. This finding, once hard to explain by natural selection, is shown to be exactly in line with predictions from natural selection theory.