Hemodynamics Flashcards
What is the study of blood moving through the circulatory system called?
Hemodynamics
Hemodynamics focuses on the movement and circulation of blood.
What does flow indicate in hemodynamics?
Volume of blood moving during a particular time
Flow measurements answer the question ‘how much?’.
What are the units for measuring flow?
/min (volume/time)
Flow is typically measured in volume per unit time.
What are the three types of flow in hemodynamics?
- Pulsatile Flow
- Phasic Flow
- Steady Flow
These flow types describe how blood moves under different conditions.
What does velocity measure in hemodynamics?
Speed or swiftness of a fluid moving from one location to another
Velocity answers the question ‘how fast?’.
What are the units for measuring velocity?
cm/s (distance/time)
Velocity is measured in distance per time.
What is pulsatile flow?
Blood moves with a variable velocity due to cardiac contraction
Commonly appears in arterial circulation.
What is phasic flow?
Blood moves with a variable velocity due to respiration
Often appears in venous circulation.
What is steady flow?
Fluid moves at a constant speed or velocity
Present in venous circulation when breathing stops briefly.
What characterizes laminar flow?
Flow streamlines are aligned and parallel with layers of blood at individual speeds
It is known as silent flow.
What are the two types of laminar flow?
- Plug flow
- Parabolic flow
These types describe specific profiles of laminar flow.
What is the Reynolds number for laminar flow?
< 1,500
A Reynolds number below this value indicates laminar flow.
What is plug flow?
All layers and blood cells travel at the same velocity
It results in a flat profile across the vessel.
What is parabolic flow?
Velocity is highest in the middle and decreases at the vessel wall
It creates a bullet-shaped profile.
What does the Reynolds number predict?
Whether flow is laminar or turbulent
It is a ratio between viscosity and inertia.
What characterizes turbulent flow?
Chaotic flow patterns with multiple directions and speeds
Associated with cardiovascular pathology.
What is the Reynolds number for turbulent flow?
> 2,000
A Reynolds number above this value indicates turbulent flow.
What is a murmur in hemodynamics?
Sound associated with turbulent flow
It can indicate abnormal blood flow.
What is a thrill in hemodynamics?
Tissue vibration associated with turbulent flow
Also known as a palpable murmur.
What is the energy gradient in hemodynamics?
Blood moves from regions of high energy to low energy
This is driven by the contraction of the heart during systole.
What determines kinetic energy in hemodynamics?
An object’s mass and speed
Kinetic energy is calculated using the formula KE = 1/2 MV².
What is Pressure Potential Energy?
A form of stored energy; has the ability to perform work; a major form of energy for circulating blood and creates flow by overcoming resistance
Potential Energy (PE) = Mass x Gravity x Height
Define Gravitational Energy.
A form of stored or potential energy associated with any elevated object
This energy is dependent on the height of the object above a reference point.
What does Viscosity describe?
The thickness of a fluid
Units: Poise
What is Viscous Energy Loss?
More energy is lost with movement of high viscosity fluids; viscous loss is associated with blood overcoming its internal stickiness; determined by Hematocrit
Higher viscosity leads to greater energy loss.
What does Hematocrit measure?
The percentage of blood made up of RBCs; normal value = 45%
Hematocrit is crucial for understanding blood viscosity.
What is Frictional Energy Loss?
Occurs when flow energy is converted to heat as one object rubs across another, i.e: blood rubbing/sliding against vessel walls
What is Inertial Energy Loss?
Energy is lost when the speed of a fluid changes, regardless of whether the fluid speeds up or slows down; occurs during 3 events:
* Pulsatile flow (arterial)
* Phasic flow (venous)
* Velocity changes at a stenosis
Define Inertia in fluid dynamics.
Relates to the tendency of a fluid to resist changes in its velocity
What is Stenosis?
A narrowing in the lumen of a vessel
What occurs during Post-stenotic turbulence?
Turbulent flow downstream from the stenosis
What does Bernoulli’s Principle describe?
A modified law of conservation of energy; describes the relationship between velocity (kinetic energy) and pressure in a moving fluid (blood)
When velocity is high, pressure is low and vice versa.
Fill in the blank: The pressure gradient is equal to _______.
flow X resistance
What happens to resistance to flow during stenosis?
Resistance to flow increases whenever there is a stenosis; in the circulatory system, the resistance vessels are called arterioles
Describe Veins in the circulatory system.
Thin-walled, collapsible, low-resistance vessels; allows for large volume increases with very small pressure increases by changing shape from an hourglass, to oval, to round as inflow increases.
What is Hydrostatic Pressure?
Pressure related to the weight of blood pressing on a vessel measured at a height above or below heart level; units: mmHG
True or False: Hydrostatic pressure is 0mmHG everywhere in a supine patient.
True
What is the effect of Hydrostatic Pressure on measured pressures in an upright patient?
Hydrostatic pressure is negative at locations above the heart, creating erroneously low measured pressures; positive at locations below the heart, creating erroneously high measured pressures
Measured pressure = circulatory pressure + hydrostatic pressure
What happens to flow direction in a stenosis?
Change in flow direction
Flow direction changes as the vessel narrows.
What occurs to velocity as a vessel narrows due to stenosis?
Increased velocity
Velocity increases as the vessel narrows.
What type of flow is observed downstream from a stenosis?
Turbulence
Turbulence is a common effect following a stenosis.
What is the pressure gradient across a stenosis?
Pressure gradient exists
A pressure gradient is present across the stenosis.
What is lost due to stenosis?
Loss of pulsatility
Pulsatility is diminished in the presence of a stenosis.
According to Ohm’s Law for fluid, what is measured at the ankle?
Pressure
Pressure measurements can be taken at various points, including the ankle.
What is the measurement site for pressure at the knee?
Knee
Pressure is also measured at the knee level.
What is the significance of the measurement at the waist?
Pressure
Waist pressure measurements are relevant for understanding hemodynamics.
What happens to thoracic pressure during inspiration?
Thoracic pressure decreases
Inhalation leads to a decrease in thoracic pressure.
What is the pressure measurement example mentioned?
140 mmHg
140 mmHg is referenced multiple times as a pressure measurement.
What is the relationship between abdominal pressure and venous return?
Abdominal pressure increases, venous return decreases
Increased abdominal pressure can lead to decreased venous return.
What happens to the diaphragm during expiration?
Diaphragm moves upward into thorax
The diaphragm’s movement affects thoracic and abdominal pressures.
Fill in the blank: During systole, flow reversal is seen during _______.
diastole
Flow reversal occurs in diastole due to pressure changes.
What is observed at area B in a stenosis?
Velocity is maximum, pressure is lowest
Area B represents the site of maximum velocity and minimum pressure.
What happens to venous flow in the legs during inspiration?
Venous flow in legs decreases
Inspiration impacts venous return dynamics.
What is the pressure at the top of the head in the context provided?
Pressure is variable
The specific pressure values vary based on the reference point.
What is the measured pressure at the far below heart level?
O mmHg
Pressure measurements can be affected by hydrostatic factors.
True or False: Pressure is higher in Area C than in Area B.
True
Area C has higher pressure compared to Area B.
