% Stenosis	Waveform	Spectral Broadening	Velocity/Ratio	Distal Waveform
Normal	Triphasic	None	None	Normal
1-19%	Triphasic	Minimal spectral broadening	<30% increase in PSV from proximal segment	Waveforms remain normal proximally and distally
20-49%	Tri/biphasic	Prominent spectral broadening	30-100% increase in PSV from proximal segment	Waveforms remain normal proximally and distally
50-99%	Monophasic	Extensive spectral broadening	>100% increase in PSV from proximal segment	Waveform becomes monophasic distally
Occlusion	No flow (pre-occlusive thump may be heard proximal to occluded segment	None	None	Collateral waveforms are monophasic with reduced PSV