At what percentage of obstruction do lower limb arterial waveform changes become biphasic?

Arterial waveforms typically change from triphasic to biphasic when there is approximately 50-75% stenosis or obstruction in the lower limb arteries. This waveform alteration occurs because the increasing arterial narrowing impairs blood flow, reducing the normal reverse flow component seen in triphasic waveforms. The biphasic pattern represents moderate disease severity and is characterized by two phases: forward systolic flow followed by early diastolic flow reversal, but with loss of the late diastolic forward flow component. This change in waveform morphology is detected during vascular ultrasound examinations and serves as an important diagnostic indicator of significant peripheral arterial disease. As stenosis progresses beyond 75%, the waveform often becomes monophasic, indicating critical stenosis. The assessment of arterial waveforms is a standard component of lower extremity arterial evaluation in vascular laboratories worldwide and helps clinicians determine the hemodynamic significance of arterial obstructions when planning interventions.