Figure 18a .

Example of reflux: the blood flow at the level of the superior petrosal sinus (SPS) shows opposite directions between inspiration and expiration; this finding shows the presence of reversed blood flow within the examined vessel between the two phases of respiration. The blood flow direction of the inferior petrosal sinus (IPS) is not detectable during expiration. The blood flow direction of the contralateral inferior petrosal sinus (CIPS) is not detectable during inspiration or expiration.