What type of flow occurs in a vessel when it widens, resulting in a Doppler shift seen above and below the baseline differently?

When a vessel widens, it can create a complex flow pattern known as helical flow. This type of flow is characterized by the movement of blood in a spiral or corkscrew pattern, which often occurs in larger vessels or areas where the geometry changes significantly, such as at bifurcations or in dilated segments of vessels.

The Doppler shift observed in helical flow shows variations above and below the baseline due to the differing angles of the blood cells relative to the ultrasound beam. As the flow spirals, some components of the blood will be moving towards the transducer while others are moving away, leading to these differences in frequency shifts. This phenomenon is indicative of helical flow and is significant in understanding blood flow dynamics and assessing vascular conditions.

In contrast, laminar flow is characterized by smooth and orderly motion, where blood travels in parallel layers with little interaction between them, resulting in a uniform Doppler shift. Turbulent flow, on the other hand, involves chaotic and irregular blood movement, producing a broad spectrum of Doppler frequencies and often a continuous spectral waveform above the baseline. Stagnant flow refers to a non-moving or very low movement of fluid, which would not produce the Doppler shifts seen in helical flow