Publications | Site Map     Research Surgery Critical Care Hemodialysis Radiology OEM About Contact FAQ's             Fig. F1: Graph that demonstrates that volume flow will decrease during a GradeII & III stenosis (75% occlusion), as flow velocity first spikes before dropping during a Graft IV stenosis (90% occlusion). (Adapted from Spencer P, Reid, J.M., “Quantification of Carotid Stenosis with Continuous-Wave (C-W) Doppler Ultrasound,”Stroke 1979; 10(3) 326=330.) FAQ Why shouldn’t I just continue using my pen-tip Doppler to assess flow preservation during aneurysm clipping surgery? The Doppler probe measures velocity, not flow. When a pen-tip Doppler is placed against the wall of a vessel exposed during surgery, it registers how fast blood is moving, not how much blood is moving. Doppler readings are unreliable, high velocities can occur despite low flows. A Doppler measurement cannot distinguish between normal diameter flows and a Grade IV stenosis (Fig. F1). Doppler will identify Grade V (occlusive or near-occlusive) stenoses, and residual flow within an aneurysm if clip placement is incomplete. However, Doppler does not quantify flow so it is impossible to compare pre- and post-clip flow values to determine if flow has been compromised.       Start receiving our Flow Matters™ Newsletter.     Print Page View Catalog          Surgery | Critical Care | Research | Hemodialysis | OEM | Publications | Customer Service      ©2007 Transonic Systems Inc.  All rights Reserved. Privacy Statement