The relation of pulsatile pressure to flow in arteries

This paper is concerned with the recording of the phasic changes in arterial flow during each cardiac cycle, and the investigation of the pressure oscillations generating this flow. The relation of pressure to flow is 'the central problem in haemodynamics' (Burton, 1952), and has never been satisfactorily resolved for arterial flow, as its oscillatory nature makes the application of Poiseuille's law invalid. The study has been confined here to the femoral artery of the dog. Direct measurements of flow have been made by following the movement of injected bubbles of oxygen recorded by high-speed cinematography (McDonald, 1952 a). Pressure gradients have been measured by simultaneous recording of arterial pressure at two points in the artery and also by electrical differentiation of the output of a capacitance manometer. Flow curves have been calculated from the gradients using equations derived by Womersley (1954), the theory of which is presented in his accompanying paper (Womersley, 1955). General agreement between observed and calculated flow curves has been found and so establishes the validity of the theoretical derivation based on general hydrodynamic principles and also justifies the method of recording flows. Preliminary accounts have been presented to the Physiological Society both of the flow curves (Helps & McDonald, 1953) and of the derivation of flow from the pressure gradients (Helps & McDonald, 1954).