Arterial pressure and volume contour relations in man during aging

Abstract

In 16 healthy young men and 10 elderly men, pressure pulses from the left brachial artery were recorded through a Cournand needle, short stiff catheter, and a Statham P23AA or P23D gauge. Volume pulses from the same segment of the artery were recorded by amplifying the changes in impedance between the tip of the insulated arterial needle and three interconnected short needles, insulated to their tips, inserted around the artery at the level of the tip of the Cournand needle. Recorded pressure and volume pulses were compared by automatic subtraction, and also by connecting them to the Y and X axes, respectively, of an additional cathode-ray tube; by this last method, each pulse described a loop figure on the screen. In the group of young men the volume pulses exceeded in relative size the pressure pulses of equal amplitude (mean ratio of areas 120:100). Thus, a typical pressure-volume loop was a dextrorotated figure; the volume ordinates were proportionately larger than the pressure ordinates, especially during diastole. This was interpreted as indicating a viscous response (or storage of energy) of the arterial wall during late systole and diastole. In the group of older men the pressure pulses had a longer upstroke time, higher systolic peak, and higher mean level of pressure (in per cent of the pulse pressure) than did the pressure pulses from the younger men. Volume pulses from the older men had identical upstroke times but a more rapid return to the diastolic endvolume than did similar pulses from young men. Thus, the mean level of the volume pulse was significantly lower in the aged, and the mean ratio of areas of volume pulses to pressure pulses of equal amplitude was 91:100. Therefore, pressure-volume loops from elderly men were levorotated figures; the volume ordinates were proportionately smaller than the pressure ordinates, especially during diastole. This was interpreted as a release of energy from the wall during diastole. The asending limb of the loop in older men was frequently composed of periods of increase in pure pressure alternating with periods of increase in pressure and volume, i.e., showed evidence of friction; administration of a ganglionic blocking agent may convert such loops to grossly normal figures. This and other evidences suggest that there is increased parietal tension in the older men, or elevated periarterial tissue pressure, and that this apparent stiffening of the wall may be altered by blocking neurogenic mechanisms. Additional comparative studies on animals of different ages with direct methods of measuring arterial diameter are needed in order to extend the present observations in man.