Cardio 2 and 3 Flashcards
What is a simple definition of volume?
How much blood there is and where it is
What is the total blood volume (on average)
5L
What is 1 blood unit?
450 mL
What is one stroke volume and how much is it?
The blood pumped with each beat
70 mL
What is the percentage of blood in the arterial system?
18% (about 0.9L)
What is the percentage of blood in the veinous system?
61% (about 3L)
What is the percentage of blood in the heart and pulmonary circulation?
9%
12%
What is cardiac output? what is the formula?
the amount of blood the heart pumps in one minute
CO = SR X SV
What is the venous return? what is the formula?
the flow of blood back to the atrium, and must be equal to cardiac output
VR = CO
What is the average CO?
CO = 5000 mL/min
Explain the series-parallel circuit organization of the body.
The blood flow is the same in the pulmonary and systemic circulation. However, in the systemic circulation, the blood flow is divided to organs depending on how much blood they need
How is flow measured?
Flow = V/T
What is the flow formula with velocity?
we are looking at a single vessel
Flow = Area X mean velocity
Why do we measure flow with mean velocity instead of velocity?
Flow velocity is not constant within a blood vessel; it is bigger in the middle and slower in the surround
List the vessel types in size order
Aorta
Arteries
Arterioles
Capillaries
Venules
Veins
Vena cava
Because we have a branching network, how does the total area vary? How does this affect velocity?
It increases dramatically in the smaller branches
Since velocity = F/A, velocity drops significantly at the capillaries
What are the advantages of having a branching network? (3)
- All cells are close to the capillary
- High total surface area for the capillary network increases the rate of diffusion
- Low velocity gives more time for diffusive exchange
What is normal arterial blood pressure, and what does each number represent?
120/80
Systole pressure / diastole pressure
What is the equation for pressure? and what are the SI and practical units?
P = force /area
Pa, mmHg
How can pressure create movement?
With a pressure gradient
Which blood vessels have major pressure drops?
The small arteries and arterioles
Which system has the greatest pressure?
pulmonary < systemic
Why does pressure oscillate?
It is caused by cardiac contractions
What is the formula for mean arterial pressure?
MAP = DP + 1/3PP
*PP = (SP-DP)
What is the definition of hydrostatic pressure?
The pressure exerted by a fluid at equilibrium at a given point within the fluid due to gravity
What is the formula for hydrostatic pressure?
P = p X g X h
What variable is not important for calculating hydrostatic pressure?
the area is not important in determining a vessel’s blood hydrostatic pressure. It only depends on the density of the fluid and height (water jet example)
What is an indirect measurement of pressure? what does it measure?
Using the sound (pressure waves) detected in the arm as the cuff deflates is a non invasive way we found of measuring SYSTEMIC blood pressure
What is a direct measurement of pressure? what does it measure?
Veinous blood pressure can only be measured with a cannula connected to a manometer in the SVC
What is the definition of perfusion pressure?
It is the pressure gradient we can find in blood vessels
What is the formula of perfusion pressure?
ΔP = Pin - Pout
Why isn’t blood always accelerating?
Because there is a lot of resistance within all blood vessels
How will perfusion pressure affect flow? Are the pressure values important here?
The flow is proportional to perfusion pressure (F= ΔP/R)
Meaning that an increased pressure gradient will increase flow. The pressure GRADIENT is important, not the values (flow is the same if Pin = 100 Pout=10 and if Pin=500 and Pout =410 since ΔP is the same in both cases)
What is the systemic circulation approximation?
In the body, Perfusion pressure would be the difference between arterial pressure and venous pressure. However, Venous pressure is so much lower that we can approximate that perfusion pressure is equal to arterial pressure:
ΔP = (Pa - Pv) ≈ Pa because Pa»_space;Pv
What is the pulmonary circulation approximation?
We can’t make an approximation about pulmonary pressure because the arterial and venous pressures have a smaller difference. It would bring to much error to make an approximation
What is the definition of resistance?
The force that counters flow
What is the formula of resistance?
R = ΔP / F
What are the 3 characteristics of laminar flow?
- All fluid flows in one direction
- Fluid near the wall moves slowly, highest flow is in the centre
- Flow is countered by friction, energy is dissipated as heat
What is Poisseuille’s law? what does it indicate?
R = (8 π v L) / A^2 = (8 π v L) / ( π r^4)
A slight change in the diameter of a blood vessel has a great impact on the resistance
What variable of the Poiseuille’s law can be changed?
Not length: a vessel length can’t be changed throughout life
Not Blood viscosity: Can be changed but is bad for the body
Radius: The radius varies in different vessels, causing changes in resistance
Resistance _______ when in series and _______ when in parallel. Why?
increases
drops
Having a parallel circuit allows for blood to have “more space” to circulate: it’s like adding a lane on a highway to reduce traffic
What are the two important factors that can make resistance in a blood vessel vary?
The radius of the blood vessels and the organization of the blood vessels
What is the definition of compliance?
How vessels change under pressure
What is the formula for compliance?
C =ΔV / ΔP
What will happen if blood is forced through a vein? why?
Think of the compliance equation, talk about all variables involved
The blood vessels will expand, having little change in the pressure (increased ΔV / same-ish ΔP) indicating high compliance. This is because veins have thin walls, easy to move
What will happen if blood is forced through an artery? why?
The blood vessels will not expand, which will dramatically increase the pressure (increased ΔV, increased ΔP) indicating low compliance. This is because arteries have thick walls that can’t adjust easily yo high volumes.
Show the process of getting a Mean Average Pressure using the concepts of hemodynamics
(1) R = ΔP / F –> ΔP = F x R
(2) ΔP = (Pa - Pv) ≈ Pa because Pa > Pv
(3) ΔP = Pa = MAP –> MAP = F x R (see (1) and (2))
(4) F = CO = SV x HR
(5) R = Total peripheral resistance (TRP)
(3) + (4) + (5): MAP = SV x HR x TRP
