Haemodynamics Nov2 M3 Flashcards
Instruments used to measure Central venous pressure (CVP) or right atrial pressure (RAP)
Intravenous bag of saline linked to a tube that connects to a three way valve and manometer (glass/plastic tube) also connected to the three way valve + catheter goes from three way valve and pushed in body to the right atrium
CVP/RAP measurement: What are we measuring if the catheter sits in the superior vena cava
We measure CVP
How CVP and RAP compare
CVP and RAP are very close but CVP > RAP (explained by fact that flow is from higher to lower pressure)
CVP/RAP measurement: First step in method
Fill catheter with fluid and fill manometer to a decently high level
CVP/RAP measurement: Second step of method (after catheter and manometer filled with fluid)
Disconnect saline bag from three-way valve and insert catheter in the body
CVP/RAP measurement: Third step of method (how to read CVP/RAP measurement)
Manometer and catheter fluid are continuous. Manometer fluid will rise (if RAP/CVP is greater) or fall (if lower) until it reaches equilibrium. Read RAP or CVP on manometer
CVP/RAP measurement: Method for reading the RAP/CVP nowadays
The whole setup is connected to a screen so you read the pressure off the screen
Perfusion pressure definition and which values drives the fluid flow
Difference in P between inlet of fluid and outlet of fluid from a tube/vessel. deltaP = Pin - Pout. Perfusion pressure drives flow and not individual Pin or Pout.
Perfusion pressure definition in relation to an organ and assumption made to measure it
Perf. pressure = arterial P - venous P. Pa»_space;»> Pv so deltaP is approx = Pa. (for ex. Pa = 100 mmHg, Pv = 5 mmHg …)
What happens to perfusion pressure and flow if Pin=Pout
Perfusion pressure (deltaP) = 0 and flow = 0
What happens to perfusion pressure and flow if Pin>Pout and we had the same value to Pin and Pout (ex. Pin + 500 > Pout + 500)
Perfusion pressure (delta P) stays the same and flow stays the same
How is atmosepheric pressure taken into account in cardiovascular situations
Considered to be 0 because will have same influence on Pinletand Poutlet. So perfusion pressure is still the same and flow is the same
Two things that influence flow
Flow = Perfusion Pressure/Resistance (Resistance determined by length, area, nature of fluid, ..)
Resistance formula and how to measure it
Resistance = Perfusion/Flow Can’t be measured
What is the use of the notion of laminar flow
Describes internal friction and viscosity of the fluid
Laminar flow explanation
In a vessel, outermost layer of fluid flow slower than innermost layers. Layer closest to/on midline of vessel has fastest flowing fluid (velocity)
How fluid layers in laminar flow interact with each other
Internal friction between the layers causes viscosity of the fluid -> heat generated ->energy lost ->pressure lost
As laminar flow progresses, how does the energy transform
Pressure energy transforms into gradual amounts of energy given to fluid in the form of heat
Other names (2) for laminar flow and why
Parabolic flow. Looking from the side, flow velocity at vessel wall is 0 and greater towards center. Smooth flow. Layers move smoothly against each other
Poiseuille’s law and Poiseuille’s formula for resistance + to which flow it applies
Flow = deltaP/R. R = 8vL/(Pi)r4, v = viscosity (internal friction of fluid - nu).Applies to laminar flow
Why and how resistance decreases in an exercising muscle
Why : Perfusion pressure doesn’t change (Pa and Pv don’t change) but flow must increase . How: Waste products like CO2 + the falling PO2 (local metabolites) in arterioles act on smooth muscle to relax them
Which vessels usually adjust their resistance to change flow and special name for such vessels
Arterioles and small arteries. Adjusting vessels are called Resistance vessels.
What nervous system controls almost all vessels in the body and what happens if you activate it
Autonomic nervous system (SP and PSS system). Activate sympathetic nervous system = smooth muscles contract, vessels decrease
Name of hormones that regulate constriction/dilation of smooth muscle around vessels and example
Vasoactive hormones. ex. epinephrine, norepinephrine, angiotensin, etc.
How pulm resistance compares to systemic resistance and why must be so
10 times lower. Bc 10 times lower pressure gradient across but want to keep the same CO
Formula for MAP (BP) with the three factors influencing it
MAP = HR x SV x TPR
How can get formula for MAP
Assume deltaP in syst circulation is MAP (bc much greater then outlet P, venous). Also, flow is CO which is HR x SV.
What can we say about the cardiovascular system when comparing it to electricity concepts + relationship between the components
Is a series-parallel system. 1) Right heart, lungs and left heart in series 2) Left heart, all organs and right heart are in series 3) Organs are in parallel with each other
What is common and what is different for two organs in series. Things to consider in Poiseuille’s law.
Share same flow but have different perfusion pressures and resistances. R = R1 + R2. deltaP = deltaP1 + deltaP2. (flow = deltaP/R)
Organs in _______ send their blood to each other and organs in _________ don’t send their blood to each other
series send. parallel do not send.
What is common and what is different for two organs in parallel. Things to consider in Poiseuille’s law. + Link with vascular tree/branching system
deltaP1 = deltaP2. 1/R = 1/R1 + 1/R2 (combined resistance is smaller than individual ones). Branching system = lower resistance (manageable for the heart)
Give cause of arterial stenosis
Atherosclerotic plaque
Consequence of arterial stenosis
Lumen size reduced, resistance increases
why have pain in heart when stenosis occurs
flow to heart is insufficient, metabolites accumulate and this gives pain. Angina pectoris.
graph of R as a function of degree of stenosis
Linear until middle degree of stenosis but then resistance increases drastically with more stenosis
Reynold’s number and how to understand it
is density x velocity x diameter divided by viscosity. Greater number = more chance of turbulent flow so factors towards turbulent flow on top.
why turbulent flow in aorta
high velocity and high diameter
problem caused by stenosis (related to turbulent flow)
resistance created by stenosis creates greater drop of flow across stenosis. Not much pressure left to supply blood to vessels even more downstream: problem.
resistance factor in turbulent flow that adds to laminar flow
(1 over area of stenosed vessel minus 1 over area of non stenosed vessel) squared
why turbulent flow problem after stenosis evolves rapidly
As drops, 1 over As increases, and also, it’s squared. The drop of P across stenosis increases a lot.
