A clinical method of studying the elasticity of large arteries.

Studies of the physical characteristics of large arteries (Roy, 1880; Bramwell, 1924; Hallock and Benson 1937) have shown that the aorta is more elastic in the young than in the elderly. As age advances the great vessels dilate while their distensibility diminishes and the range of pressure over which the wall is approximately elastic is reduced. These changes are the result of the tension in the arterial wall being thrown on to the collagen fibres as the elastic tissue deteriorates. Clinical studies of arterial elasticity have been made by Bramwell and Hill (1922). Their method was based upon the velocity of transmission of the pulse wave, which is determined by the physical properties of the vessel wall. The pulse wave velocity was found to increase with age (Bramwell et. al., 1923 b) and with the elevation of pressure across the wall of the artery (Bramwell et. al., 1923 a and c). This work contributed much to the understanding of the effect of age upon the arterial tree; it confirmed, in vivo, the arterial changes, described earlier, in excised strips of aorta, and showed that loss of elasticity was not confined to the aorta and its immediate branches, but spread to the smaller and more muscular vessels, for example, from the brachial to the radial arteries. The consequence of this is seen in the well-known increase of pulse pressure with age Unfortunately, the elasticity of the large arteries cannot be assessed by pulse pressure measurements alone since the latter are affected by other variables such as stroke volume, the force and duration of ventricular ejection, the peripheral resistance, and the volume of the great vessels. The test to be described attempts to establish clinically whether the vessels forming the main arterial reservoir are mainly elastic or whether the tension is being thrown on to the inelastic collagen. The differentiation depends upon changes in pulse pressure occurring in vessels when the level of diastolic pressure is reduced with little change in stroke volume. From the data obtained by Roy (1880), Hallock and Benson (1937), and Remington et al. (1948) it is possible to predict that in young, more or less elastic arteries little change in pulse pressure would occur as the blood pressure was reduced without changing stroke volume, whereas in elderly, inelastic arteries progressive diminution in pulse pressure would be seen as the diastolic pressure fell. This theoretical basis of the …