Hemodynamics and Ultrasound Physics Flashcards

This set explores hemodynamic principles including blood flow patterns, energy forms/losses, stenosis effects, hydrostatic pressure, and the influence of respiration on venous flow.

Pulsatile Flow

Blood flow that moves with a variable velocity, accelerating and decelerating specifically as a result of cardiac contraction, commonly appearing in the arterial circulation.

Phasic Flow

Blood flow that moves with a variable velocity, accelerating and decelerating specifically as a result of respiration, often appearing in the venous circulation.

Steady Flow

Fluid moving at a constant speed or velocity, such as water in a garden hose or blood in the venous circulation when an individual stops breathing briefly.

Laminar Flow

A flow pattern where streamlines are aligned and parallel, characterized by layers of blood traveling at individual speeds, typically found in normal physiologic states.

Plug Flow

A form of laminar flow that occurs when all of the layers and blood cells travel at the same velocity.

Parabolic Flow

A laminar flow pattern with a bullet-shaped profile where velocity is highest in the center of the lumen and decreases to a minimum at the vessel wall.

Reynolds Number

A value used to predict whether flow is laminar or turbulent; it is less than $1,500$ for laminar flow and greater than $2,000$ for turbulent flow.

Turbulent Flow

Chaotic flow patterns in many directions and speeds, often characterized by obliterated streamlines and associated with cardiovascular pathology or significant stenosis.

Eddy Current (Vortex)

Small, hurricane-like, swirling, rotational patterns that appear in turbulent flow.

Bruit or Murmur

The sound associated with turbulent flow, created by the conversion of flow energy into sound.

Thrill

Known as a palpable murmur, this is a tissue vibration associated with turbulence that can be felt with the fingertips.

Energy Gradient

The difference that causes blood to move from regions of higher energy to regions of lower energy.

Kinetic Energy

Energy associated with a moving object, determined by an object's mass and the speed at which it moves.

Pressure Energy

A form of stored or potential energy that has the ability to perform work, acting as a major form of energy for circulating blood to overcome resistance.

Gravitational Energy

A form of stored or potential energy associated with any elevated object.

Viscosity

A measurement of the thickness of a fluid, determined in blood by the hematocrit and measured in units of Poise.

Hematocrit

The percentage of blood made up of red blood cells, with a normal value of approximately $45\%$, determining the viscous energy loss in blood.

Frictional Energy Loss

Energy loss that occurs when flow energy is converted to heat as blood slides across vessel walls.

Inertial Energy Loss

Energy loss relating to the tendency of a fluid to resist changes in its velocity, occurring during pulsatile flow, phasic flow, and velocity changes at a stenosis.

Stenosis

A narrowing in the lumen of a vessel that causes changes in flow direction, increased velocity, turbulence downstream, and a pressure gradient.

Bernoulli's Principle

Derived from the principle of conservation of energy, it states that with steady flow, the sum of kinetic energy and pressure energy remains constant, meaning pressure is lowest where kinetic energy (velocity) is highest.

Pressure-Flow Relationship Equation

$$\text{pressure gradient} = \text{flow} \times \text{resistance}$$

Ohm's Law

An electrical relationship equivalent to fluid hemodynamics, defined as $\text{voltage} = \text{current} \times \text{resistance}$.

Arterioles

The specific vessels in the circulatory system known as resistance vessels.

Hydrostatic Pressure

Pressure related to the weight of blood pressing on a vessel measured at a height above or below heart level, reported in units of $mmHg$.

Supine

Describes an individual lying flat on their back, where hydrostatic pressure is $0\,mmHg$ everywhere in the body because all parts are at heart level.

Standing Hydrostatic Pressure (Ankle)

In an upright individual, the hydrostatic pressure at this site far below heart level is approximately $100\,mmHg$.

Standing Hydrostatic Pressure (Head)

In an upright individual, the hydrostatic pressure at this site above the level of the heart is approximately $-30\,mmHg$.

Inspiration

The phase of breathing where the diaphragm moves downward, thoracic pressure decreases (increasing venous return to the heart), and abdominal pressure increases (decreasing leg venous flow).

Expiration

The phase of breathing where the diaphragm moves upward, thoracic pressure increases (decreasing venous return to the heart), and abdominal pressure decreases (increasing leg venous flow).