Unit 18 Hemodynamics :: Ultrasound Physics with Sononerds

About this video

• Video Title: Unit 18 Hemodynamics :: Ultrasound Physics with Sononerds
• Channel: Sononerds
• Speakers: M (from Sononerds)
• Duration: 01:14:55

Overview

This video provides a comprehensive explanation of hemodynamics, the study of blood flow through the circulatory system. It covers fundamental concepts like volume flow rate and velocity, fluid dynamics principles including viscosity, pressure, and resistance, and introduces the Poiseuille and Bernoulli equations. The video also details different types of blood flow (laminar and turbulent), the impact of vessel considerations like anatomy and respiration on flow, and the role of hydrostatic pressure. Finally, it discusses energy loss, stenosis, and the physiological significance of these hemodynamic principles in ultrasound physics.

Key takeaways

• Volume Flow Rate and Velocity: Understanding how much blood is moving (flow rate) and how fast it's moving (velocity) are crucial for comprehending Doppler ultrasound.
• Fluid Dynamics Principles: Concepts like viscosity (resistance to flow), pressure (driving force), and resistance (opposition to flow) are fundamental to blood flow.
• Poiseuille Equation: This equation relates flow rate to pressure gradient, resistance, vessel length, viscosity, and radius, highlighting how changes in these factors affect blood flow.
• Types of Flow: Blood flow can be laminar (smooth, parallel streamlines) or turbulent (chaotic, swirling flow), with Reynolds' number predicting which type is likely to occur. Turbulent flow is often associated with stenotic areas and can be heard as a bruit or felt as a thrill.
• Energy and Stenosis: The law of conservation of energy applies to blood flow, with energy losses occurring through viscous, frictional, and inertial mechanisms. Stenosis (narrowing of a vessel) leads to increased velocity, turbulent flow, pressure gradients, and loss of pulsatility, all of which can be detected with ultrasound.
• Hydrostatic Pressure: Gravity influences blood pressure, with pressure increasing below heart level and decreasing above it. This concept is vital for accurate blood pressure measurements.
• Vessel Anatomy and Respiration: The muscular walls of arteries (allowing vasoconstriction/vasodilation) and the flexibility of veins, along with respiratory changes in thoracic and abdominal pressure, significantly influence blood flow patterns, particularly in the venous system.