What effect does ICA occlusion have on diastolic flow in the CCA spectral display?

When there is an occlusion of the internal carotid artery (ICA), the expected effect on the common carotid artery (CCA) spectral display is the elimination of diastolic flow. In a healthy vascular system, diastolic flow is present due to the continued perfusion of blood during the relaxation phase of the cardiac cycle. However, with ICA occlusion, blood flow dynamics are drastically altered due to the increased resistance upstream.

The occlusion reduces or completely obstructs the flow to the ICA, leading to a significant drop in pressure and reduced perfusion downstream into the CCA. As a result, the normal diastolic flow which is usually represented on the spectral Doppler display diminishes or disappears entirely, reflecting a more critical perfusion state and the physiological impact of the obstruction.

In this context, while other answers may imply varying degrees of diastolic flow characteristics, the key indication of ICA occlusion is the marked reduction or complete elimination of diastolic flow, making the choice specifically relevant to the pathophysiological changes occurring in the vascular system during significant occlusive events.