SCT II - Circulation Flashcards
Equation of Mean Arterial Pressure
Mean Arterial Pressure = Cardiac Output x Total Peripheral Resistance
CO = HR x SV
What other way could we calculate Mean Arterial Pressure?
MAP (Mean Arterial Pressure) = DP (Diastolic Pressure) + 1/3 PP (Pulse Pressure)
PP (Pulse Pressure) = SP (Systolic Pressure) - DP (Diastolic Pressure)
How do you calculate TPR?
Resistance = 8/π * Lƞ/r^4
L - Length of vascular system
ƞ - Viscosity of blood
r - Radius of vessel
How different is the viscosity of blood in vivo and in vitro?
In vivo, blood is 1.25x more viscous than water
In vitro, blood is 2.5x more viscous than water
RBC tend to be in the center of the flow, in tubes there is no flow
How can the equation of MAP be converted to adapt to a single organ?
ΔP (Pressure of Organ) = Φ (Flow of Organ) x R (Resistance of Organ)
Poiseuille Law
ΔP = (8 x L x ƞ x Φ) / π x r^4
ΔP - Pressure Gradient
L - Length of Vascular System
ƞ - Viscosity of Blood
Φ - Flow of Blood
r - Radius of Vessel
Reynold’s Number
Re = (v x D x ρ) / ƞ
v - Velocity of Flow
D - Diameter of Vessel
ρ - Density of Blood
ƞ - Viscosity of Blood
What is special about the diameter in the equation of Reynold’s Number?
Diameter has a negative correlation with Reynold’s Number due to its effect on Velocity (4-fold)
Think of pressing onto the exit of a hose to increase water velocity
What are Korotkoff Sounds?
Sounds heard during the measurement of blood pressure; compressing the vessel to decrease the diameter, increasing the velocity, increasing Reynold’s number, and hence making the flow turbulent and easy to listen to
What are the two types of turbulent flow that can be helpful in diagnostics?
- Korotkoff Sounds
- Murmurs (heart, valves, etc.)
What is compliance?
Ability to stretch
How do you calculate compliance?
C =ΔV / ΔP
C - Compliance
V - Volume
P - Pressure
Explain compliance vs Distensibility
Compliance = Distensibility x Volume
How much more compliance do veins have? And why?
Veins have 24x compliance than arteries
8x more Distensible
3x more Volume (capacity)
In the central pulse wave, what is the name and cause of the little notch after systolic pressure?
Incisura
Closure of aortic valve
What type of wave is the central pulse wave? Why is it like that?
Dicrotic wave
1. Anacrotic limb (ascending pressure)
2. Catacrotic limb (descending pressure)
What qualities should you check for a pulse?
Rhythm
- Rhythmic or arhythmic?
Frequency
- Frequent or rare?
Amplitude
- Low or high?
Rate of Rise
- Slow or fast rise?
Compressibility
- Hard or soft?
Equality
- Equal or unequal on both arms
What happens during aortic stenosis?
SV DECREASES
SP DECREASES
DP UNCHANGED
PP DECREASES
Ejection becomes turbulent, resulting in a SYSTOLIC MURMUR
What is aortic regurgitation (insufficiency)?
The aortic valve fails to close and therefore there is backflow of blood
What happens during aortic insufficiency?
DP DECREASES
EDV INCREASES
SV INCREASES
SP INCREASES
PP INCREASES
Rate of Ejection INCREASES
Backflow is turbulent, resulting in a DIASTOLIC MURMUR
What happens during atherosclerosis?
Hardening of artery
COMPLIANCE DECREASES
DP INCREASES
SP SUPER-INCREASES
PP INCREASES
Rate of Rise INCREASES
Similar to aortic insufficiency
Describe the relationship between velocity and surface area
Velocity ~ 1/Surface Area
Explain continuous, fenestrated, and discontinuous capillaries
Continuous: Tight cells, rigid basement membrane
Fenestrated: Spaced cells, rigid basement membrane
Discontinuous: Spaced cells, spaced basement membrane
How do large amounts of material move in bulk flow?
Move in response to pressure (area of high pressure to low pressure)
Faster than diffusion/osmosis
Important for the regulation of extracellular fluid
Explain oncotic pressure
Pressure due to proteins - proteins pull substances towards them
Explain hydrostatic pressure
Pressure due to fluids - higher intensity of flow, higher the pressure
What’s the primary role of Starling forces?
Forces decide which way the fluid will move (secretion/absorption)
Which starling forces are in favor of filtration?
Interstitial Fluid Colloid (Osmotic Pressure) + Capillary (Pressure)
Which Starling forces are in favor of absorption?
Interstitial Fluid (Pressure) + Plasma Colloid (Osmotic Pressure)
Which path does Pnet take?
Pnet = Pc - Pif
Pnet - Total hydrostatic pressure
Pc - Capillary hydrostatic pressure
Pif - Interstitial fluid pressure
Pnet <3 Pc - Favors FILTRATION
Which path does πnet take?
πnet = πc - πif
πnet - Total oncotic pressure
πc - Capillary oncotic pressure
πif - Interstitial fluid pressure
πnet <3 πif - Favors ABSORPTION
What is the equation of effective filtration pressure?
Peff = Pnet - πnet
Peff - Effective filtration pressure
Pnet - Net hydrostatic pressure
πnet - Net oncotic pressure
If Peff > 0 - Filtration
If Peff < 0 - Absorption
Along the length of a capillary, what happens to Pc and πc?
Pc decreases (> 2/3 – <1/3)
πc stays the same (< 2/3 – >1/3)
Why does πc stay the same throughout the capillary?
Proteins cannot move through the compartments, staying constant throughout the length of the capillary
What can cause edema?
Two things:
1. Either filtration»_space;»» absorption
2. Lymphatic passage problems
What could cause filtration»_space;»> absorption
- Pnet increase
- πnet decrease
What can increase Pnet?
Vasodilation
1. Extremely high temp (arteries dilate to lose heat)
2. Sympathetic tone damage (inhibits vasoconstriction)
3. Vasodilating drugs
4. Beri-Beri (B1-Thiamine Deff.)
What can increase πnet?
Venous end
1. Compression of veins
2. Blockage of veins
3. Right/Left Ventricular Failure, Systemic & Pulmonary (respectively)
What can decrease πnet?
Hypoproteinaemia
1. Bad diet; malnutrition
2. Liver diseases; produces proteins
3. Nephrotic syndrome; proteins are filtered into piss… not good
How can venous tone increase venous return?
Sympathetic tone causes vasoconstriction, blood depots are activated, increasing VR, increasing EDV
What is the physiologic CVP (Central Venous Pressure)?
-2 - 6 mmHg
Reduced CVP risk
Risk of shock and hemorrhage
Increased CVP risk
Risk of right ventricular failure
What regulates the vascular tone?
Resting Vasoconstriction
1. Basal tone (myogenic)
Spontaneous contractility of smooth muscle cells of the vessel
- Resting vasoconstrictor tone (neurogenic)
SNS innervation
What happens during reflex vasoconstriction?
Increase in the action potentials through the sympathetic nerves causes increase in contraction (consitrctions)
What causes vasodilation?
- Base tone DECREASES
- Resting vasoconstrictor tone DECREASES
- Vasodilator nerves are ACTIVATED
What causes vasoconsitrction?
- Base tone INCREASES
- Reflex vasoconstrictor ACTIVATED/INCREASED
What regulates the basal tone?
It’s myogenic, so the smooth muscle regulates itself
At what locations does the SNS provide vasoconstrictor nerves?
- Arteries
- Arterioles
- Most organs
- Veins
At what locations does the SNS provide vasodilation nerves?
- Skeletal muscle
- Certain glands
Explain redistribution of blood during fight-or-flight
Cardiac output is redistributed to mainly supply the muscles:
Kidney: vasoconstrict = less blood
Liver: vasoconstrict = less blood
Skin: vasoconstrict = less blood
Muscles: vasodilate = more blood
Which locations are you able to find PNS vasodilator nerves?
- Erectile tissue
- Pia mater (meninges)
What happens during axon reflex?
Injury triggers axon to release histamine and substance-p, which activate vasodilation to increase blood flow to the wound for quicker repair
