Blood flow

Blood flow is the volume of blood passing through a vessel or tissue per unit of time. It transports oxygen, nutrients, hormones, and heat while carrying away waste products.

Perfusion pressure: The pressure difference that drives blood through an organ or vascular bed. The pressure gradient between arterial and venous sides drives tissue blood flow.
Cardiac output: The volume of blood pumped by the heart per minute. It is the total flow through the systemic or pulmonary circulation per unit time.
Doppler ultrasound: An imaging method that uses frequency shifts in reflected sound to assess motion, including blood flow. It estimates flow direction and velocity without inserting a probe into the vessel.
Tissue perfusion: The passage of blood through a tissue's microvascular network. Perfusion describes blood delivery at the tissue level rather than flow in a single vessel.
Volumetric flow rate: The volume of fluid passing through a surface per unit time. Blood flow is a biological instance of this general physical quantity.
Vascular resistance: The opposition to blood movement through a vessel or vascular network. Resistance determines how much flow a given pressure gradient produces.
Blood pressure: The force blood exerts on the walls of blood vessels. Pressure supplies the gradient that drives blood through the circulation.
Laser Doppler flowmetry: A technique that estimates microvascular blood flow from Doppler shifts in laser light scattered by moving blood cells. It measures local perfusion in small tissue regions, especially in skin.
Blood flow velocity: The distance blood travels through a vessel per unit time. Velocity and volumetric flow are related but differ because vessel cross-sectional area matters.
Transit-time flow measurement: A technique that estimates vessel flow from the travel-time difference of ultrasound waves moving with and against flow. It provides a direct intraoperative estimate of flow in an accessible vessel.

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