Doppler waveform of the brachial vein with and without a tourniquet

Longitudinal ultrasound images of the right arm with color and spectral Doppler show normal venous waveforms in the brachial vein. The artery (deep to the vein) is the same color as the vein due to arterial pulsatility and the portion of the cardiac cycle captured. A) Without tourniquet, there is mild pulsality in the venous waveform reflecting right atrial pressures, but no sharp upstroke. B) When a tourniquet is applied, the waveform becomes flat.