Blood Flow and Pressure Flashcards
What is the flow rule?
- circulatory system = closed system
- pressure = force exerted by blood
- flow occurs from high pressure to low pressure
Flow =
- ΔP/R
- ΔP is the force pushing blood against various factors resisting the flow of liquid in a pipe
- R is resistance to flow (factors that hinder flow)
The heart creates a _____ for bulk flow of blood.
pressure gradient
A ______ must exist throughout the circulatory system to maintain blood flow.
gradient
What are the 2 pressure gradients in the systemic circuit?
- aortic pressure = mean arterial pressure (MAP)
- pressure in veins in thoracic cavity = central venous pressure (CVP)
What is typical MAP?
85 mm Hg
What is typical CVP?
- 2-8 mm Hg (negligible)
- vena cavae = 0 mm Hg
ΔP (in systemic circuit) =
= MAP - CVP
= 85 - 0 = 85 mm Hg
- because CVP is so small, it is generally ignored; MAP = ΔP
What is the ΔP?
pressure in aorta minus pressure in vena cava just before it empties into right atrium
What are the pressure gradients in the pulmonary circuit?
- pulmonary arterial pressure (PAP) = 15 mm Hg
- pulmonary venous pressure (PVP) = 0 mm Hg
ΔP (in pulmonary circuit) =
= 15-0 = 15 mm Hg
Which one is higher: ΔP in systemic circuit or ΔP in pulmonary circuit?
ΔP in systemic circuit
____ through both circuits is equal
- flow
- flow = ΔP/R
Since flow = ΔP/R and flow through both circuits is equal, this means…
resistance through the pulmonary circuit is much less than resistance though the systemic circuit
Name 3 factors affecting resistance to flow.
- radius of vessel
- length of vessel
- viscosity of fluid
Describe how the radius of vessel could affect resistance.
in arterioles (and small arteries), can regulate radius
Describe how the viscosity of fluid can affect resistance.
- Viscosity of fluid = η
- blood viscosity depends on amount of RBCs and proteins: usually constant
What are the 2 types of regulation of the radius of arterioles (and small arteries)?
- vasoconstriction
- vasodilation
What is vasoconstriction?
decreased radius –> increased resistance
What is vasodilation?
increased radius –> decreased resistance
What is total peripheral resistance (TPR)?
resistance of all blood vessels in systemic circuit
How does flow through network vary with resistance?
- vasoconstriction in network = increased resistance = decreased flow
- vasodilation in network = decreased resistance = increased flow
CO = , since ΔP = ___ and R = _____
= ΔP/R or MAP/TPR, since ΔP = MAP and R = TPR
TPR =
= MAP/CO
= 85/5
= 17 mm Hg per L/min (blood flow)
What lines the inner layer of the wall in all blood vessels?
endothelial cells
Name 3 other components of blood vessel walls.
- smooth muscle
- fibrous connective tissue (collagen)
- elastic connective tissue (elastin)
Name 2 structural features of arteries.
- large diameter
- little resistance
In arteries, walls contain ____ and ____ tissue. Why?
- elastic and fibrous tissue
- under high pressure
Name 3 features of muscular arteries.
- less than 0.1 mm in diameter
- little elastin
- smooth muscle regulates radius
What is compliance?
a measure of the relationship between pressure and volume changes
Low compliance in arteries means:
a small increase in volume = large increase in pressure
Arteries are a _____ reservoir.
pressure
Artery features that enable energy/pressure storage are:
- structure
- response during systole and diastole
How do arteries respond during systole?
expand as blood enters arteries during systole
How do arteries respond during diastole?
recoil during diastole
High compliance in veins means:
a large increase in blood volume is required to produce a large increase in pressure
Pressure in the aorta varies with ____ _____.
cardiac cycle
When is the pressure in the aorta at its maximum? Why?
- systolic blood pressure
- due to ejection of blood into aorta
When is the pressure in the aorta at its minimum? Why is it not 0?
- diastolic blood pressure
- not 0 due to elastic recoil
How is arterial blood pressure measured?
BP = SP/DP
What is average arterial BP?
120/80
Pulse pressure =
SP - DP
MAP =
[SP + (2 x DP)]/3
Why do we multiply DP by 2?
DP is twice as long as SP
What is average MAP?
[120 + (2 x 80)]/3 = 93.3 mm Hg
What is the driving force for blood flow?
MAP
Regulating ___ is critical to normal function.
MAP
MAP < normal means:
- hypotension
- inadequate blood flow to tissues
MAP > normal means:
- hypertension
- stressor for heart and blood vessels
What are the sounds heard for systolic pressure in measuring BP?
beginning of sounds
What are the sounds heard for diastolic pressure in measuring BP?
distinct change in sounds
If cuff pressure is above 110 mm Hg, what would we find?
- no blood flow
- no sound
If cuff pressure is between 70 and 110 mm Hg, what would we find?
- turbulent flow
- audible vibrations (Korotkoff sounds)
If cuff pressure is below 70 mm Hg, what would we find?
- laminar flow
- no sound
Arterioles are ____ vessels
resistant
Arterioles > ___% TPR
60%
What are arterioles?
- part of microcirculation
- connect arteries to capillaries or metarterioles
What structural feature do arterioles have to regulate pressure?
ring of smooth muscle
Arterioles have the largest pressure drop in vasculature, from ___ mm Hg to ___ mm Hg.
90 mm Hg to 40 mm Hg
