Hemodynamics study guide- Witwer Flashcards
Potential Energy of blood is a combination of intravascular pressure of blood and _______
gravitational potential energy of blood
Intravascular pressure is secondary to (list 4 things)
- Cardiac contraction
- The Hydrostatic (water) Pressure of the blood
- Static filling pressure of blood
- Friction
Pressure arising from cardiac contraction produces CO and _______
vascular resistance
Hydrostatic (water) pressure of the blood =
pressure exerted by blood in closed circulatory system
Hydrostatic pressure Equation
= (minus) specific gravity of blood x acceleration due to gravity x height above specific reference point
- *specific gravity of blood is it’s weight compared to the weight of water
- *Acceleration= acceleration of blood due to gravity
Static filling pressure of blood is the pressure that exists because of the amount of blood in the ______
vessel, and the elasticity of the blood vessel wall
Gravitational Potential Energy of Blood=
capacity of blood to do work based on its position above a reference point
Gravitational Potential Energy (equation)
=plus specific gravity x acceleration due to gravity x height above specific reference point.
______ and ______ are added together to get the total potential energy of blood.
Gravitational Potential Energy and Hydrostatic Pressure of Blood
**Often cancel one another out
Fluid Energy of blood is equal to=
the sum of the Kinetic Energy and Potential Energy.
Blood Flow is a function of the total _____ energy in the vascular system
fluid
Energy in the Blood Stream is in three interchangeable forms:
1) Pressure secondary to cardiac output, elasticity of the vessel walls, and peripheral vascular resistance – this is perpendicular (lateral) pressure on vessel walls, called the transmural (across the wall) pressure
2) Hydrostatic Pressure from gravitational forces
3) Kinetic Energy of Blood Flow – remember this is largely related to the velocity of the blood, ie greatest in the ascending aorta
When are gravitational forces important regarding a Patient?
only in the standing person (orthostatic hypotension, Coldstream Guards, passing out when standing).
They are not important in the horizontal patient.
In clinical practice the Pt is assumed to be ____
supine (negating the gravitational component of pressure) and at rest (kinetic energy is negligible compared to blood pressure at normal cardiac output).
–>Eliminating these and simplifying the equation allows you to estimate pressure gradients by determining velocities above and below an obstruction
Blood flow is also a function of a pressure gradient and ______
resistance
Blood flows from an area of ______ pressure to one of _____ pressure
higher to lower
– I.E. (From the Left Ventricle to the Right Atrium)
Blood Flow is described by measuring the:
total volume of blood pumped by the ventricle per minute, ie the Cardiac Output.
CO equation
CO= SV x HR
Stroke volume=
volume of blood ejected from the left ventricle in one cardiac cycle
Cardiac Index corrects for?
Patient size.
-Cardiac index= CO/patient’s Body Surface Area
Describe Blood Flow:
In a closed hydraulic system
the blood flow at any given point (aorta, arteries, arterioles, capillaries, venules, veins, vena cavae) will be equal to the flow at any other point
The volume of blood moving past a reference point in a specified unit of time
is equal to the..
Pressure Gradient divided by Resistance
MAP - Central venous pressure (CVP)=
CO x Systemic Vascular Resistance (SVR)
MAP can be estimated by using MAP=
=[1/3 x Aortic Systolic Pressure] + [2/3] xAortic Diastolic Pressure]
Septic shock has high CO but low ____
SVR
Cardiogenic shock has a low CO but high____
SVR
Continuity Equation
States that the blood flow past any given point (see above) is proportional to the velocity of flow times the cross sectional area. Also, from above, the blood flow at any given point will be equal to the flow at any other point, therefore:
Q(Flow) = Area1 x Velocity1 = Area2 x Velocity2 = Area3 x Velocity3
CO is equal to =
SV (volume of blood ejected from the left ventricle in one cardiac cycle – ml ejected per contraction) times the HR (beats per minute).
Thus, this is the total volume of blood pumped by the ventricle in one minute (Liters/minute).
Blood composes _% of body weight
7%
-Amount of blood depends on age, gender, weight, and height.
-Generally, men have 4.5 to 6.0 quarts and women have 3.5 to 4.0 quarts.
A quart is .95 Liters, therefore, men have about 4.3-5.7L and women about 3.3 – 3.8L
A “unit of blood” is roughly
1 pint, ie 473 ml
Arterial vascular resistance=
Resistance to blood flow in the cardiovascular system
**Takes place primarily in the arterioles
Changes in ______ are the most important quantitatively for regulating blood flow
vessel diameter (Poiseuilles’s Law)
Pulsatile blood flow in the arteries occurs secondary to ____
cardiac contractions
Describe laminar blood flow in arteries
Blood flows in layers (lamina) within the arterial lumen (channel, opening of hollow tube). Friction between the layers results in a parabolic flow profile.
The flow resistance in laminar flow is due to_______
viscous resistance, ie, the viscosity of blood.
Doppler flow meters measure?
parabolic flow velocity but calculate an average velocity of a cross section of the vessel, NOT the maximum velocity
Blood flow in the arteries is blunted by turbulence secondary to:
narrowing and tortuosity of vessels
Describe elasticity of arterial walls
Is the stretchability of arterial walls determined by the elastic fibers in the Tunica Media. Force causing the stretch called stress.
–>Stretched walls return to the original state
BP is dependent on:
stroke volume, compliance and elastic rebound of aorta (dicrotic notch), and resistance to blood flow (primarily in the arterioles)
Pulse pressure=
Systolic Pressure minus Diastolic Pressure
Blood pressure can get a slight “boost” from
elastic rebound of blood vessel
The Dicrotic notch=
a dip in the aortic waveform. The aorta then has an elastic rebound and a brief reversal of blood flow. See slides.
BP control: there are both _____ and _____ regulatory mechanisms
intrinsic and extrinsic
Intrinsic mechanisms
Blood flow in most tissues is proportional to metabolic needs
Extrinsic mechanisms
- Nervous system
- Hormonal Control
Intrinsic Regulation of Blood Flow (autoregulation)
-Vasodilatation leads to increased flow when tissue senses:
Chemical changes, decreased Oxygen, decreased pH or increased Carbon Dioxide or lactic acid or Nitrous Oxide.
-Vasoconstriction occurs when tissue senses:
Chemical changes, increased Oxygen, increased Sympathetic stimulation, vasopressin, angiotensin II, and cold
Provide specific examples of Extrinsic regulation of blood flow
- Sympathoadrenal stimulation increases cardiac output and increases total peripheral resistance.
- Baroreceptor and chemoreceptor responses
- Renin Angiotensin Aldosterone System
- Atrial Natriuretic Peptide mechanism
Baroreceptor reflex adjusts not only the HR, but the _____
mean arterial pressure (MAP) by altering the force and speed of heart contractions and total peripheral resistance
Renin-Angiotensin-Aldosterone System is activated when there is..
decreased blood flow, blood volume, and/or blood pressure to the kidneys.
-Renin and angiotensin work to stimulate increased peripheral resistance by vasoconstriction creating an increase in blood pressure. Aldosterone stimulates kidneys to retain water via sodium retention and potassium excretion (water follows sodium) causing increased blood volume and increased blood pressure.
Where are baroreceptors located?
in low pressure receptor zones (atria, vena cavae, and pulmonary veins)
Baroreceptors regulate?
secretion of antidiuretic hormone, renin, and aldosterone causing increase in blood volume and increased blood pressure.
Epinephrine and Norepinephrine from the Sympathetic Nervous system stimulate:
cardiac contraction and peripheral vascular smooth muscle to increase blood pressure
Blood volume is decreased by____
diuretics
RAAS is treated by:
Angiotensin Converting Enzyme (ACE) Inhibitors and Angiotensin II Receptor antagonists
Spironolactone is an aldosterone ______
inhibitor
Beta Blockers (Sympatholytics) block?
epinephrine receptors
Describe the distribution of Vascular Resistance
50-60% of resistance to blood flow is in small arteries and arterioles
25% of resistance is in capillaries
20% of resistance is in large arteries
5% of resistance is in veins
Where will the largest drop in BP occur?
in the arterioles–> where there is also the most dramatic increase in cross sectional diameter
Small arteries and arterioles have ______ which makes their vascular beds most responsive to active resistance to blood flow.
smooth muscle
Resistance to blood flow is greatest at the ______ level
arteriolar level (50-60%)
Other causes of resistance to blood flow include friction and _________
Viscosity–> Thickness of the blood, from sticky. More energy is required to pump thick blood than thin blood.
Thick blood is found when _____ is high
hematocrit is high (Polycythemia)
-and/or there is an increased concentration of protein molecules in the blood (Multiple Myeloma)
What is the most significant component of resistance?
vessel radius
Turbulence is another cause of resistance secondary to ________
irregular vessel walls, and/or tortuous and/or narrow (stenotic) vessels
Turbulent flow causes a loss of energy—> thus a drop in ____
BP distal to the stenosis
In order to maintain perfusion in the face of turbulence, greater _____ is required.
pressure
The sounds of turbulence include:
- heart murmurs
- the Korotkoff sounds when measuring BP
Resistance to Blood Flow is estimated by Poiseuille’s Law:
Pressure Gradient = 8 Q L V/π r4
Q is the flow through the segment
L is the length of the segment
V is the viscosity of blood, generally the viscosity of blood is 3 to 4 times greater than the viscosity of water, and is a function of hematocrit
Π is pi
r is the radius of the vessel. The 4th power makes the radius the greatest effect on resistance.
Poiseuille’s Law: as length and viscosity increase–> ______ increases
resistance
Smaller vessels have increased resistance. Therefore, the ateriolar bed is where _____
most resistance actively occurs as the arteriole has constricting smooth muscle that makes the radius smaller (there are no muscles in the capillary walls)
Atherosclerosis _____ the vessel radius therefore ________ resistance
- narrows
- increasing
-When the diameter of the vessel is 50% or more, it becomes hemodynamically significant.
Collateral vessels have greater length and thus ____ resistance.
greater
Interestingly, the Brain and Kidneys are ___ resistance systems. For their size, they thus receive a disproportionately large amount of blood.
low
