[Damping of oscillations in arterial pressure in the internal carotid arteries]

In dogs, recording of fluctuations of the inlet and outlet pressure in the internal carotid artery showed a decrease of the amplitude of fluctuations along the artery, the damping index (Id) being about 60-90%. The Id was almost unchanged when the skull was either intact or largely opened. The amplitude of blood pressure fluctuations in the circle of Willis was always decreased after occlusion of the vertebral arteries, being evidently unrelated to superposition of the pulse waves that reach the circle of Willis through the internal carotid and the vertebral arteries. Therefore the decrease of the amplitude of pulsation was dependent on the damping of the pulsatile waves along the internal carotid arteries. The rise of the tone of the latter increased the Id, and vice cersa. The Id was almost independent of the size of amplitude and of the frequency of the fluctuations of the systemic arterial pressure, but decreased when the latter rised.