Hemodynamics Flashcards
Bernoulli’s principle says that energy can be changed but not ____
Destroyed
Per Bernoulli’s principle, as ____ of fluid flow increases, there is a coexisting reduction in ____
velocity; pressure
Bernoulli’s principle states there will be an ____ in kinetic energy with a ____ in pressure at the site of an obstruction to flow
increase; decrease
Based on the conservation of energy principle: If ____ or ____ changes, there will be a change in the other energy to maintain the same level of total energy
pressure or kinetic energy
According to Bernoulli’s equation, ____ and ____ are inversely related
Velocity and pressure
If a vessel has plaque causing a narrowing, the flow velocity will ____ at the site of a stenosis so the pressure must ____
increase; decrease
What do we use Bernoulli’s principle to predict?
- The pressure drop (gradient) between two chambers
What does Bernoulli’s principle determine?
- Max and mean pressure gradients across stenotic valves
- Max pressure gradients across regurgitant valve lesions and abnormal shunt communications
What does Bernoulli’s principle estimate?
Intracardiac pressure
What is the modified Bernoulli’s equation?
∆P = 4 (v2^2 - V1^2)
What is the simplified Bernoulli’s equation?
∆P = 4(V2^2)
What does ‘P1’ stand for?
Pressure at location 1
What does ‘P2’ stand for?
Pressure at location 2
What does ‘ρ’ stand for?
Density of the blood (1.06 x 10^3 kg/m^3)
What does ‘V1’ stand for?
Velocity of location 1
What does ‘V2’ stand for?
Velocity of location 2
When is modified Bernoulli’s equation used?
Typically used with aortic stenosis when V1 is > 1.2 m/s
When is simplified Bernoulli’s equation used?
When V1 is </= 1.2 m/s
What does P1 - P2 = ?
∆P; or Q
What is the pressure in the left ventricle?
120 mmHg
What is the pressure in the aorta?
100 mmHg
What is the pressure in the arterioles?
45 mmHg
What is the pressure in the capillaries?
10 mmHg
What does ‘Q’ stand for?
Flow volume
Arterial Blood Pressure is determined by ____ and ____
Volume of blood and resistance
Equation for pressure
Pressure = flow (vol/min) x resistance
What is resistance?
The amount of pressure exerted against flow
What is distensibility?
Stretching of arteries or veins to accommodate more blood (systole)
What is elasticity?
The ability of a vessel to bounce back after being stretched
What is stroke volume (SV)? (definition)
The amount of blood pumped out of the heart per beat
What is the equation for stroke volume?
LVOTd^2 x .785 x LVOT⌄TVI
What is the normal range for stroke volume?
70-100 cc
What is cardiac output (CO)? (definition)
The amount of blood pumped by heart per minute
What is the equation for cardiac output?
SV (cc) x heart rate (HR) / 1000
What is the normal range for cardiac output?
4-8 L/min
What is cardiac index (CI)? (definition)
The cardiac output adjusted for Body Surface Area (BSA)
What is the equation for cardiac index?
Cardiac Output (CO) / BSA
What is the normal range for cardiac index?
2.4 - 4.2 L/m/m^2
What are the three resistance factors?
Viscosity, friction, and inertia (acceleration and deceleration)
What is viscosity?
The thickness of blood
What is friction?
Movement of blood against the vessels will change some pressure energy to heat
- there is some loss of the pressure energy to friction
longer, narrower vessels cause ____ friction
more
What is inertia?
property of all matter; an object at rest tends to stay at rest, an object in motion tends to stay in motion
- there is some loss of the energy pressure as inertial losses
What causes inertial losses
acceleration and deceleration
What is Poiseuille’s Law?
States that flow volume (Q) varies directly with the pressure gradient (Pi-Po) and the fourth power of the radius of the tube (r). Flow (Q) varies inversely with the length (L) of the tube and the viscosity (n) of a fluid.
What does (Pi - Po) stand for?
Pressure gradient
What does ‘n’ stand for?
Viscosity
What is Poiseuille’s law equation?
Q = (Pi-Po) πr^4 / 8nL or
∆P = Q8nL / πr^4
What is Poiseuille’s Law simplified?
- As pressure gradient ↑ flow volume ↑
- As the tube diameter ↑, flow volume ↑
- As the length of the tube ↑, flow volume ↓
- As fluid viscosity ↑, flow volume ↓
Of all of the factors that effect blood flow, the ____ of the blood vessel is the most significant!
radius
What is velocity? (definition)
distance moved over a period of time
What is the equation for velocity?
velocity = distance x time (V=DxT)
What is the unit for velocity?
cm/min or M/min
What is flow? (definition)
amount of blood over time
What is the equation for flow?
flow = volume/time (F=V/T) or
flow = pressure ÷ resistance
What is the unit for flow?
mL/min or L/min
The less resistance blood meets, the ____ the flow
greater
Slow flow is important in ____ for the exchange of nutrients and wastes
Capillaries
Due to reduction in total cross-sectional area (diameter/radius), pressure ____ in the veins until blood reaches the right atrium
Decreases
Pressure in the venules is ____ than it is in the larger veins
Higher
____ of veins from capillary bed to IVC/SVC continues to become larger, helping create the energy gradient needed to move flow toward the heart
Diameter
What is the contraction of the heart during systole, causing blood to surge and strike the arterial walls called?
Pulsatile flow
The more dramatic the rise and fall of velocity during systole and diastole, the greater the ____
Pulsatility
This surge can be palpated at points where an artery is close to surface of the skin. As the surge of blood passes and diastole occurs, arteries contract and return to pre-systolic shape/area.
Pulsatile flow
____ flow occurs further from the heart, especially in the capillaries
Steady
Steady flow is essential for proper exchange of ____ and ____
Nutrients and waste
____ do not normally pulsate
Veins
____ flow (no change with respirations) in a vein may indicate deep vein thrombosis
Steady
How is blood flow affected by a stenosis?
Blood becomes turbulent which reduces the velocity
Conservation of energy theory
Energy can be changed, not destroyed
At stenotic lesion (decrease in diameter) what happens to velocity and pressure? What type of flow pattern is it?
- Velocity is increased
- Pressure is decreased
- Disturbed flow pattern
At the exit of a stenotic lesion (increase in diameter) what happens to velocity and pressure? What type of flow pattern is it?
- Velocity decreases
- Pressure increases
- Turbulent flow pattern
In order for a stenosis to be hemodynamically significant (patient has signs and symptoms) , it must be ___% reduced in diameter and ___% reduced in area.
50% reduced in diameter
75% reduced in area
What is energy?
The capacity to do work
What is potential?
The ability to do work
The faster blood moves, the more ____ energy (pressure) is turned into ____ energy
Potential; kinetic
As blood enters a stenosis (dramatically reducing size of vessel), two things occur:
- Blood changes direction to enter
- Blood changes direction to exit
Usually found at entrance of a great vessel (aorta)
Inlet/Plug flow
During what flow is the velocity of cells at wall similar to velocities in center of vessel
Inlet/Plug flow
As vessel size decreases and changes direction, cells at the wall slow in comparison to velocities in center of vessel
Parabolic flow
Exists when cells move in a forward direction but not in organized layers, as in movement over small amounts of wall plaque
Disturbed flow
Occurs when the fluid particles move in multiple directions at different velocities. Vortices (whirling blood flow) or Eddies (small circular currents) may develop at turbulent sites.
Turbulent flow
Reynold’s number (Re)
Predicts the onset of turbulence by using the following four factors
velocity (v), density (p), radius (r), and viscosity (n)
In cardiovascular imaging, ____ and ____ are constant
Fluid density and viscosity
What is the equation for Reynold’s number (Re)?
Re = flow speed x tube radius x fluid density ÷ fluid viscosity
A Reynold’s (Re) value of ____ or greater indicates turbulence
2000
Resistance
Force that exists against layers of moving blood
Peripheral resistance
Walls of blood vessels offer the most resistance to blood flow
The ____ a blood vessel, the more resistance the blood flow meets
Smaller
Important function of the body is to control ____ blood pressure
Arterial
Reflexes in the body change the diameter of ____ to help regulate blood pressure
Arterioles
Arteriole diameter changes either increase or decrease ____ ____
Peripheral resistance
Arteriole diameter changes are controlled by the ____ ____ in the brain
Vasomotor center
Stimuli are transmitted to the smooth muscle of the vessel wall via the ____ nervous system
Sympathetic
Vasodilation
Increase in vessel diameter decreases peripheral resistance and lowers blood pressure
Vasoconstriction
Decrease in vessel diameter increases peripheral resistance and raises blood pressure
Lowers heart rate, controls digestion
Parasympathetic nerves
Increases heart rate, force of heart contraction, controls amount of contractions occurring in arteries and veins
Sympathetic nerves
What is collateral blood flow?
If an artery becomes blocked or occluded, other adjacent vessels may pick up the blood flow
Collateral routes are more ____ to flow
Resistant
What is resistance to flow?
The ratio of the pressure gradient across a vessel segment
What is the equation for resistance of flow?
Rseg = (P1 - P 2) / Q (flow)
The cardiac cycle includes all ____ and ____ events in one heartbeat
Electrical and mechanical
____ events precede ____ events.
Electrical; mechanical
____ events are graphed on the EKG
Electrical
P wave represents ____ ____
Atrial contraction/ atrial systole
QRS represents ____ ____
Ventricular depolarization
ST segment represents ____
Isoelectric period when the heart is refractory to electrical stimulation
T wave represents ____ ____
Ventricular repolarization (recovery phase of ventricle)
What is the definition of Isovolumic Relaxation (IVRT)
The time period between semilunar valve closure and MV and TV opening.
This time period represents early ventricular relaxation.
Isovolumic Relaxation (IVRT)
When does ventricular pressures drop below arterial pressures with no change in ventricular volume.
Isovolumic Relaxation (IVRT)
What are the three components of ventricular diastole?
- Rapid, early diastolic filling-blood enters ventricles passively, yet quickly due to swift ventricular relaxation (E wave)
- Reduced filling –flow is reduced, pressure begins to equalize (Deceleration of E wave)
- Diastasis (Time between E and A waves) Seen in slow heart rates
- Atrial systole
____% of ventricular filling occurs during the rapid, early diastolic filling phase
70%
The period when the ventricles are filling with blood. On the EKG begins with the end of the “T” wave and ends with the onset of the “QRS” complex.
Ventricular diastole
When are the MV and TV are open and the semilunar valves are closed?
Ventricular diastole
Occurs at the end of ventricular diastole with the onset of the “P” wave of the EKG.
Atrial Systole
When are the MV and TV open, and the semilunar valves are close?
Atrial Systole
Atrial systole contributes ____% of ventricular filling
30%
The time period between MV and TV closure and semilunar valve opening.
Isovolumic Contraction
When are all cardiac valves are closes as the ventricles begin to contract.
Isovolumic Contraction
During isovolumic contraction there is an increase in ____ pressure until ____ pressure is exceeded with no change in volume
Ventricular; arterial
When does ventricular systole begin?
Begins with the closure of the AV valves
What corresponds with the onset of the QRS to the T wave on EKG?
Ventricular systole
Events during ventricular systole occur as follows:
- Isovolumic contraction (IVCT)
- Rapid ejection
- Reduced ejection
Rapid ejection
Semilunar valves open, rapid rise in pressure
Reduced ejection
Peak ventricular ejection, pressure begins to drop until it’s below great vessel pressure and then the semilunar valves close
