A spectral Doppler waveform is the graphical display produced by pulsed wave or continuous wave Doppler, showing blood flow velocities on the vertical axis plotted against time on the horizontal axis. The waveform shape reflects the pulsatility of flow in the vessel. High-resistance vessels (such as peripheral arteries at rest) show sharp systolic peaks and absent or reversed diastolic flow. Low-resistance vessels (such as the internal carotid artery or renal arteries) show broad systolic peaks with continuous forward diastolic flow.