Hemodynamics Flashcards
What 4 variables influence hemodynamics?
pressure
compliance
velocity of blood flow
resistance
Poisuelle’s Law
How does the LV generate pressure?
pressure is generated to move blood through tubes through arterial side and back to the RA
How does the RV generate pressure?
RV generates pressure that circulates blood through pulmonary circulation through lungs
What happens to transmural pressure (T.P.) when standing?
T.P. above the heart is lower
T.P. above the heart is higher
What is an outside influence on B.P.?
Gravity
Define: Blood Pressure
pressure produced when LV contracts
pressure in vasculature
Define: Transmural Pressure (TP)
pressure across the wall
What happens to BP and TP at heart level?
they are equal when standing or sitting
What happens to BP and TP while lying down?
they are equal
above heart → both 99 mm Hg
at heart → both 100 mmHg
below heart → both 98 mmHg
What happens to BP and TP while standing?
- Above Heart
- BP → 99 mmHg
- TP → 69 mmHg
- At Heart
- BP → 100 mmHg
- TP → 100 mmHg
- Below Heart
- BP → 98 mmHg
- TP → 198 mmHg
Is compliance higher in veins or arterial system?
veins
Equation: Compliance
Compliance = ΔV/ΔP
Define: Compliance
characteristic of any hollow organ or vessel
lowest when volume in chamber is smallest
as you fill a chamber closer to its max volume, compliance will be reduced
What is the most compliant part of the arterial system?
Thoracic aorta
70/40 = 1.75
What happens when you increase you increase sympathetic stimulation to the veins?
NE is released → NE binds α1 receptor → cause contraction of smooth muscle → decrease in vein compliance
Why is compliance less important to arteries?
B/c they have less blood
it primarily effects shape of aortic pressure pulse
What happens if you increase sympathetic tone to arterial side?
increases resistance
Why is compliance important to veins?
if you decreases compliance of the veins → walls become more rigid → pressure increases → increases venous return to heart → preload increases → SV increases → CO increases
What is the relationship between a cross sectional area and velocity flow?
inverse
area increases → velocity of flow decreases
area decreases → velocity of flow increases
What system has the largest cross sectional area?
capillaries → slowest velocity → helps drive diffusion
What are the 2 components to pressure of flowing blood?
lateral or static
kinetic
what happens to kinetic component at a higher flow velocity?
it is greater
What happens when a patient has atherosclerotic plaque?
Increased velocity flow → lateral pressure (to kidneys) drops → kidneys get less blood flow → can cause HTN
What occurs during narrowing of aortic valve?
contraction is restricted → increased velocity blood flow → reduce lateral blood flow
Equation: Resistance
resistance = ΔP(pressure)/Q(volume flow)
To get resistance in whole circulatory system (systemic circulation), where would you need to measure pressures in order to know ΔP?
Assume pressure in aorta is 120/80 and RA pressure is ~ 2mmHg
System starts in the aorta → need to know mean/avg pressure in aorta (maBP= diastolic + ⅓ PP)
maBP = 80 + ⅓(40) = 93 mmHg
system ends where vena cava enters RA
TPR = ΔP/Q= (93-2)/5 = 91/5
Equation: maBP
maBP = diastolic + ⅓ PP
Equation: Pulse Pressure
Systolic - Diastolic
Equation: TPR
TPR Δ in pressure across the system
TPR = ΔP/Q
What does resistance depend on in the circulatory system?
arterioles (are they constricted or relaxed)
What do you regulate by changing resistance?
pressure and volume flow
What happens if you constrict arterioles?
Pressure in aorta increases
pressure in capillaries decreases
volume flow through arterioles drops
What are the special conditions required for Poiseuille’s Law to apple?
- Flow is non-pulsatile (no flow variations with time)
- Flow is laminar
- The fluid is a newtonian fluid (homogeneous fluid such as water; no a suspension like blood)
What variables does Poiseuille’s Law relate?
pressure
length of tube
radius of tube
viscosity of the liquid
Does the circulatory system meet the criteria for Poiseuille’s Law?
No, but the relationships still influence blood flow
What does flow through a tube depend on?
inflow and outflow pressures
What happens to volume flow if you double the pressure and increase the height of a system?
double the flow
What happens to volume flow if you reduce the difference of a system?
pressure of flow decreases
What happens to volume flow if there is no difference in pressure and hieght of a system?
there is no flow
What is the relationship between flow and ΔP?
they are directly proportional
they greater the ΔP, the greater the flow
What is the relationship between length of the tube and volume flow?
inverse relationship
Increase tube length, decrease flow
What is the relationship between radius of the tube and volume flow?
directly proportional
increase radius, increase flow
What is the relationship between viscosity of the liquid and volume flow?
inversely proportional
increase viscosity, decrease flow
Define: Viscosity
a measure of how difficult it is to separate lamina (relatively constant in circulatory system)
How does liquid flow in a tube?
faster in the center
slower on the periphery
What effect does hematocrit have on viscosity?
Increase hematocrit, increase viscosity
can change viscosity by changing hematocrit
Define: Hematocrit
percent of RBCs present in blood
Equation: Velocity flow
Q = π(Pi-Po)r4/8nl
r = radius
l = length
n = viscosity
Which variable from the volume flow equation varies the most in the circulatory system?
r4
Where does the greatest change in pressure occur?
Arterioles
How are resistors organized in a circulatory system?
in parallel
What would happen if the resistors were organized in series?
total resistance of a series = sum of all resistors
more organs in series → greater resistance → increase work for heart → increase metabolic demands → less efficient
What does the resistors being in parallel allow the circulatory system to do?
It allows varying flow to different organs
adding another resistor reduces heart work
What are the parts of the arterial pulse wave?
Incisura or Dicrotic notch → aortic valve closes, ejection phase ends
Dicrotic wave → Dicrotic notch to diastole
Systolic pressure → highest pressure during 1 cardiac cycle ,increases as you move away from heart
mean pressure → diastolic + ⅓PP
diastolic pressure → lowest pressure
What happens to compliance of the aorta as you move away from the heart?
it decreases
What are peripheral arterial blood pressure and volume flow affected by?
Changes in vascular compliance, total peripheral resistance, and stroke volume
