Hemodynamics & Instrumentation - Video Notes (Vocabulary flashcards)

Key terms and concepts from the video lecture on vascular hemodynamics, arterial/venous flow, Doppler instrumentation, and common artifacts.

Hemodynamics

The study of the movements of blood and the forces involved in regulating blood flow.

Flow (Q)

Volume of blood moving through a vessel per unit time; Q = velocity × cross-sectional area; driven by pressure gradient.

Pressure gradient

Difference in pressure between two points that drives flow; flow goes from high to low pressure; larger gradient increases flow.

Energy (in hemodynamics)

The capacity to do work; energy is conserved and can take forms such as potential energy (pressure) and kinetic energy (velocity).

Potential energy (Pressure)

Energy stored in blood due to pressure within vessels.

Kinetic energy (Velocity)

Energy due to the motion of blood, related to its velocity.

Energy Conservation

Net energy in the vascular system remains constant; energy is transformed, mainly dissipated as heat due to friction.

Flow equation (Continuity)

Q = V × A; flow is the product of velocity and cross-sectional area; the vascular system tends to maintain flow.

Bernoulli Principle

Relationship among energy, velocity, and pressure; as pressure decreases, velocity increases (and vice versa); assumes flow with minimal friction.

Pressure vs Velocity (Bernoulli)

Pressure is potential energy; velocity is kinetic energy; their relationship helps explain how changes affect flow.

Poiseuille’s Law

Q = (ΔP) π r^4 / (8 μ L); describes laminar flow in cylindrical vessels; depends on pressure difference, radius^4, viscosity, and length.

Radius and flow (r^4)

Flow is proportional to the fourth power of the vessel radius; small changes in radius cause large changes in flow.

Viscosity (μ)

Internal friction of blood; part of Poiseuille’s law; affects resistance to flow.

Resistance

Opposition to flow; increases with length and viscosity and decreases with radius (R ∝ L μ / r^4).

Length

Longer vessel length increases friction and resistance, reducing flow.

Reynolds number (Re)

Dimensionless number predicting flow regime; Re < ~2000 is laminar, Re > ~2000 tends to become turbulent.

Laminar flow

Smooth, orderly flow with a parabolic velocity profile and a thin boundary layer at the walls.

Plug flow

A velocity profile common in large arteries where layers accelerate together, producing a flattened (plug-like) profile.

Turbulent flow

Swirling, chaotic flow often occurring distal to a stenosis; associated with a large pressure drop; typically Re > 2000.

Post-stenotic turbulence

Turbulent flow just distal to a significant stenosis; may be accompanied by elevated velocity.

Arterial mean pressure (MAP)

Average arterial pressure around 70–100 mmHg; a driving force for tissue perfusion.

Flow patterns (arterial)

Laminar, Plug, and Turbulent flow patterns describing how blood moves in arteries.

High resistance waveform

Multiphasic Doppler waveform with flow reversals due to reflections; seen in peripheral vessels.

Low resistance waveform

Monophasic Doppler waveform with flow in one direction throughout the cardiac cycle; example: internal carotid artery.

Dampened (Tardus-Parvus) waveform

Distal to severe stenosis: delayed upstroke and reduced peak velocity.

Post-stenotic turbulence (cardio)

Turbulent flow downstream of a stenosis, contributing to a velocity drop and energy loss.

Venous hemodynamics

Low-pressure venous system (mean ~5–15 mmHg) influenced by hydrostatic pressure, valves, chest pressure changes, and calf pump.

Hydrostatic pressure

Pressure due to the weight of blood; HP = ρ g h; affects arteries and veins and increases when standing.

Transmural pressure

Transmural = intraluminal pressure − interstitial pressure; governs vessel caliber and wall tension.

Respiratory effects on venous return

Inspiration lowers intrathoracic pressure, can reduce venous return from legs; expiration increases abdominal pressure and venous return.

Calf muscle pump

Contraction of calf muscles that propels venous blood toward the heart, aiding return.

Venous valves

Valves within the veins that prevent backflow and help maintain venous return.

Venous waveforms

Phasic waveforms that are influenced by respiration; pulsatile near the heart; lack of phasicity suggests proximal obstruction.

Circulatory system

Closed loop including heart, aorta, arteries, arterioles, capillaries, venules, veins, and vena cava.

Doppler shift

Change in frequency due to moving reflectors (RBCs); positive toward the transducer, negative away; strongest at 0°; 60° max recommended.

Pulse-wave Doppler (PW Doppler)

Doppler technique using pulses to sample at a depth; allows depth selection; can exhibit aliasing if Doppler shift exceeds half PRF.

PRF (Pulse Repetition Frequency)

Number of ultrasound pulses transmitted per second; sets Nyquist limit for Doppler sampling.

Aliasing

Artifactual wrap-around of Doppler spectrum when Doppler shift exceeds ½ PRF; corrected by increasing PRF or lowering Doppler shift.

Doppler controls (PW)

PRF/Scale, Gate, Sample volume, Spectral gain, Baseline, Angle correction.

Color Doppler

PW Doppler technique that displays velocity as color; blue/red indicate flow direction relative to transducer; aliasing possible near stenosis.

Color Doppler controls

PRF/Scale, Gate/Sample volume, Color gain, Packet size, Priority, Persistence.

Doppler artifacts

Reverberation, Shadowing, Partial volume artifact, Wall clutter/motion, Color bleeding/blooming, Mirror image.

Reverberation

Echoes caused by multiple reflections, creating artificial, evenly spaced echoes.

Partial volume artifact

Signal from structures partly within the ultrasound slice thickness, causing misleading echoes in Doppler.

Mirror image artifact

Duplicated signal across a strong reflector, creating a phantom image.

Wall clutter & motion

Low-frequency artifacts at vessel walls caused by tissue motion or persistent echoes.