What are the functions of the circulatory system?
transport of
 nutrition, O_{2}, CO_{2}, metabolites
 thermoregulation (= transport of heat)
 hormones (= endocrinological function)
 cells of immune system (= immunological function)
What is the twopump system?
Explain.
simplified model for cardiovascular system
 2 pumps in series: right, left ventricle
 2 vascular beds in series: systemic, pulmonary vasculature
→ flow pumped in both systems virtually equal to each other
Elaborate on the following parameters of the aorta:
 diameter, thickness of wall
 amount of elastic tissue
 amount of smooth mm.
 number
 cross sectional area [cm^{2}]
 percentage of blood volume
Elaborate on the following parameters of arteries:
 diameter, thickness of wall
 amount of elastic tissue
 amount of smooth mm.
 number
 cross sectional area [cm^{2}]
 percentage of blood volume
Elaborate on the following parameters of arterioles:
 diameter, thickness of wall
 amount of elastic tissue
 amount of smooth mm.
 number
 cross sectional area [cm^{2}]
 percentage of blood volume
Elaborate on the following parameters of capillaries:
 diameter, thickness of wall
 amount of elastic tissue
 amount of smooth mm.
 number
 cross sectional area [cm^{2}]
 percentage of blood volume
Elaborate on the following parameters of venules:
 diameter, thickness of wall
 amount of elastic tissue
 amount of smooth mm.
 number
 cross sectional area [cm^{2}]
 percentage of blood volume
Elaborate on the following parameters of veins:
 diameter, thickness of wall
 amount of elastic tissue
 amount of smooth mm.
 number
 cross sectional area [cm^{2}]
 percentage of blood volume
Elaborate on the following parameters of the vv. cavae:
 diameter, thickness of wall
 amount of elastic tissue
 amount of smooth mm.
 number
 cross sectional area [cm^{2}]
 percentage of blood volume
Elaborate on the following parameters of the vessels of the pulmonary circulation:
 amount of elastic tissue
 amount of smooth mm.
 percentage of blood volume
What percentage of blood volume can be found in the heart?
7%
→ approx. 350  450 ml
Although hemodynamics are a powerful tool to describe physics of blood/fluid flow through the circulatory system, they are not 100% exact.
Why is that?
bc in vessels
 flow is pulsatile: pressure P, flow Q are not constant
 wall is not rigid due to el. tissue: radius r, cross sectional area A can be changed
 blood is a nonnewtonian fluid: velocity v is not always constant
Explain the relationship btw velocity and the crosssectional area.
equation of continuity
conservation of mass causes fluid flow to be constant in every 2 sections of a tube
→ velocity inversely proportional to crosssectional area
Q = A * v
A * v = constant
BUT: same applies if A_{2} is spread among many vessels
Relate the velocitycrosssectional area relationship in a graph.
 velocity decreases in arterial system
 minimal value in capillaries
 velocity increases in venous system
What does the lowest point of the velocity graph indicate?
Value?
lowest v (= 0.3 mm/s) in capillaries
→ longest time (1  3s) for diffusion btw circulatory system and peripheral tissues
What are the types of pressure in a tube?

static pressure P_{stat}: pressure if fluid is not moving or if object is moving w/ the fluid dynamic pressure P_{dyn}: pressure of a fluid that results from its motion
→ P_{stat} + P_{dyn} = P_{total}
lecture guy referred to static pressure as side pressure
How can dynamic pressure be calculated?
dynamic pressure is directly proportional to density and velocity
P_{dyn} = 1/2 ⍴ v^{2}
 ⍴ = density
 v = velocity
BUT: usually negligible in most arterial locations
Describe the effect of velocity on static pressure in a tube.
Which law describes this relationship?
Bernoulli's law states that if the v is increased a decreased P_{stat }can be measured
↑v → ↓P_{stat}
because:
 ↑v → ↑P_{dyn}
 P_{stat} + P_{dyn} = P_{total}
 conservation of E
Which relationship is described by HagenPoiseuille's law?
Formula.
describes flow of fluid in terms of
 ΔP (P_{i}  P_{o}) = pressure gradient btw inlet and outlet
 r = radius of the tube
 ƞ = viscosity of the fluid
 l = length of the tube
NOTE: radius is the critical factor
(raised to the 4th power)
Give the formula for hydraulic resistance in fluid mechanics.
ability of vessels to fluid flow
R = ΔP/Q
 ΔP = pressure gradient btw inlet and outlet of tube
 Q = flow
⇒ resistance is inversely proportional to fluid flow
How can the resistance of vessels be calculated using HagenPoiseuille's law?
Formula + unit.
Hagen's Poiseuille's law can be plugged in to formula for hydraulic resistance to substitute fluid flow, pressure gradient can be cancelled out
in [R unit] (instead of mmHg*sec/ml)
 ƞ = viscosity of fluid
 l = length of tube
 r = radius of tube
NOTE: radius is the critical factor
(raised to the 4th power)
What is the consequence of HagenPoiseuille's law w/r/t the resistance in various blood vessels?
depends mainly on vessel diameter
 highest resistance in capillaries
 diminishes as vessels incr. in diameter on art./ven. sides of capillaries
Name 2 mechanisms that can change the diameter of a vessel.

contraction of circular smooth mm. in the vessel wall

transmural pressure = pressure difference btw int./ext. pressure, hence ↑P_{int} w/o incr. P_{ext} → dilation of vessel
How can resistances in series and parallel be calculated?
in series: R_{T} = R_{1} + R_{2} + R_{3} + ...
in parallel: 1/R_{T} = 1/R_{1} + 1/R_{2} + 1/R_{3} + ...
⇒ total resistance = less than individual resistances bc additional pathways for fluid flow are provided
NOTE: R_{T} = total peripheral resistance
Although capillaries are usually arranged in parallel with one another, there are 2 exceptions.
Which ones?

renal vasculature: peritubular capillaries are in series w/ glomerular capillaries

splanchnic vasculature: intestinal are in series w/ hepatic capillaries
What is total peripheral resistance?
Formula and unit.
What is the consequence?
ratio of arteriovenous pressure difference to cardiac output (according to ΔP = Q * R), reciprocal of 1/R_{T}
TPR = P_{atrial}/cardiac output
→ if CO constant, change in TPR can modify P_{atrial}
What does the Reynold's number describe?
Formula.
describes the tendency of flow to be laminar or turbulent
 N_{R} > 2000 → laminar
 N_{R} > 3000 → turbulent
N_{R} = ⍴dv/ƞ
 ⍴ = density of fluid
 d = diameter of vessel
 v = mean velocity of fluid
 ƞ = viscosity
Describe how the velocity of laminar flow behaves.
most central layer moves most rapidly (double mean velocity of flow across entire cross section)
bc thin layer of fluid adhering to wall/slower layer → shear force, slowing down next, more central layer
What is the significance of turbulent flow?
How can it be caused?
greater pressure required to force a given flow through same tube (higher workload on heart)
+ causes sounds
 anemia → ↓ƞ → ↑N_{R}
 stenosis → ↓A → ↑v → ↑N_{R}
 BP measurement → ↓A → ↑v → ↑N_{R}
AND: thrombi are more likely to develop in turbulent flow
What is shear stress?
Formula.
blood flow through a vessel causes a force on the wall parallel to the wall = shear stress
τ = 4ƞQ/πr^{3}
 ƞ = viscosity of the fluid
 Q = fluid flow
 r = radius of the vessel
NOTE: radius is the critical factor
(raised to the 3th power)
Which properties of the vasculature are described by the YoungLaplace equation?
Why is it clinically relevant?
relates the wall tension to the shape of the surface
T = P*r/2x
 P = internal pressure
 r = radius of the vessel
 x = wall thickness
in case of aneurysm: incr. r → ↑T → ↑r → ↓x
→ ↑↑T → vessel eventually bursts
What does the distensibility of a vessel describe?
Formula.
ability of a vessel to change its volume under transmural pressure → elastic properties
D = (ΔV/V_{0})/P in [%]
 ΔV/V_{0} = ratio of volume change and initial volume
 P = transmural pressure
What is the difference btw compliance and distensibility of a vessel?
Formula.
Compare the compliance of veins and arteries.
 distensibility refers to volume change as a ratio to its initial volume
 compliance only describes the relative volume change (= slope of PV diagram)
C = ΔV/ΔP
 ΔV = volume change
 ΔP = pressure difference
Compare compliance and distensibility of systemic, pulmonary veins and arteries in a graph.
Explain.
compliance = slope of PV diagram
 D_{veins} = 8x D_{arteries}
 C_{veins} = 25x C_{arteries}
 C_{pulm} > C_{syst}
although arteries have much greater amount of elastic tissue than veins, veins are usually not fully distended
→ can alter shape from ellipsoid to circular
BUT: only in physiological range
("true" D, C_{veins} < D, C_{arteries})
What are standard physiological pressure and volume changes in the venous and arterial system?
venous system:
 ΔP = 15 mmHg
 ΔV = 2500 ml
arterial system:
 ΔP = 100 mmHg
 ΔV = 500 ml
List and briefly explain different ways to measure the blood flow.

bloody method: collecting venous outflow, timing the collection w/ a stopwatch

electromagnetic flow meter: most frequently used, based on electromagnetic induction principle

Doppler flow meter: measuring linear velocity
⇒ invasive
 Fick's method: X added to blood, rate at which X passes a checkpoint measured + calculated
 dilution method: dyes used to measure organ's circulation
⇒ noninvasive
List the 2 types of vessels w/r/t their conducted blood flow in response to changes in pressure.
Compare their characteristics in a graph.

elastic vessels (= lungtype vessels) = "normal" vessel type

autoregulated vessels (= kidneytype vessels) = able to adapt their behavior
Explain the behavior of elastic vessels referring to the graph below.
↑P → ↑r (dilation) → ↓R
⇒ exponential curve, tangent of each point would show decreased R
Explain the behavior of autoregulated vessels referring to the graph below.
Where can we find such vessels?
vascular smooth m. cells contract autonomously in response to mechanoreceptors to maintain local blood flow within a narrow range → active process
(in physiological P range, 50  150 mmHg)

↑P → ↓r (contraction) → ↑R
avoids waste of perfusion into organs in which flow is already sufficient 
↓P → ↑r (relaxation) → ↓R
maintains capillary flow + capillary pressure
⇒ can be found in organs sensitive to ischemia, hypoxia (brain, kidney, heart)
How is the radius of arterioles regulated?

myogenic resting tone: caused by autoregulation

sympathetic tone: caused by symp. innervation via α_{1} and β_{2} receptors
BUT: tissue dependent
Compare the hematocrit dependence of the relative viscosity of blood in vivo and in vitro.
Values for rel. viscosity of plasma at 0 and physiological Ht.
relative viscosity increases with increasing Ht level,
BUT: in vivo lower viscosity due to moving RBCs
(RBCs move faster than blood, hence lower proportion)
 blood plasma at 0% Ht, ƞ = 1.2ƞ_{water}
 blood plasma at 45% Ht, ƞ = 3ƞ_{water}
_{REMEMBER: bridge analogy}
What is shear thinning?
Explain its effect on RBCs.
the greater the flow, the greater shear stress
(cf. shear stress)
→ RBCs accumulate in most central lamina, hence greatest velocity (only in vessels < 300μm)
⇒ enhances deformability of RBCs, able to fit through 3μm capillaries although 7μm in size
_{↑ [fibrinogen] incr. deformability of RBCs}
How does the viscosity in the different types of vessels behave?
shear thinning in vessels (cf. own card)
→ lowest viscosity in smallest vessels
What is the function of the aorta and other large arteries?
Explain.
convert intermittent pulsatile cardiac output to a steady flow = Windkessel effect
 distend when the blood pressure rises during systole
 recoil when the blood pressure falls during diastole
since Q_{entering} > Q_{leaving} (due to the TPR)
⇒ net storage of blood during systole (40ml) which discharges during diastole
Draw and explain the pressure curve of the aortic system.
average heart rate = 75/min → heart beat = 0.8s
 systole = 0.27s (ends w/ incisura), phase of isometric contraction, rising P (80 → 120 mmHg)
 diastole = 0.53s, dropping P back to 80 mmHg
 incisura = small pressure drop due to closure of aortic valve
List the different types of blood pressure and explain.
Values.

P_{syst} = 120 mmHg, highest point of curve

P_{dias} = 80 mmHg, lowest point of curve

P_{pulse} = 40 mmHg = ΔP_{dias, syst}

P_{mean} = 93 mmHg = mean arterial pressure, in resting conditions P_{syst}/P_{dias} = 1:2,
BUT: heartrate dependent: if ↑HR 1:1
BUT: heartrate dependent: if ↑HR 1:1
List ways to measure the blood pressure.
 transducers
 sphygmomanometry
Explain the blood pressure measurement using a sphygmomanometer.
Another name.
RivaRocci method
inflatable cuff (+ stethoscope)
 wrapped around arm, a. brachialis occluded
 pressure slowly declines
 2 methods:
 palpatory method: pulse of a. radialis can be felt at wrist (= systolic pressure)
 auscultatory method: 2 Korotkoff sounds can be heard (1st = systolic, 2nd = diastolic)
Explain transducer measurements to determine the blood pressure.
catheter connected to a closed chamber w/ a diaphragm, amplifier, recorder
 catheter introduced into vessel
 diaphragm converts mech. strain into an electrical signal
 signal amplified + recorded
Distinguish btw parameters that determine arterial blood pressure.
physiological parameters
 cardiac output (stroke volume * HR)
 TPR
⇒ act through physical parameters
physical parameters
 blood volume
 compliance
What is the reason for the Windkessel effect in the aorta and large arteries?
Show how it changes during life using a graph.
high elastin content → high compliance
BUT: as people age elastin content reduced, replaced by collagen → reduced compliance
⇒ ↑ P_{syst}, ↓ P_{dias}, ↑↑P_{pulse} (cf. own card)
Describe the effect of changed stroke volume on the blood pressure, presumed that HR and arterial compliance remain constant.
Relate it in a graph.
volume that enters art. system exceeds volume that leaves system
 ↑↑ P_{syst}
 ↑ P_{dias}
 ↑ P_{pulse}
 ↑ P_{mean}
Describe the effect of changed TPR on the blood pressure, presumed that arterial compliance remains constant.
However since arterial compliance is only linear in young people, describe its effects in the elderly.
Relate it in a graph.
in young:
 ↑ P_{syst}
 ↑ P_{dias} (proportionally to ↑P_{syst})
 constant P_{pulse}
 ↑ P_{mean}
in elderly: sim. effects to ↑ stroke volume
 ↑↑ P_{syst}
 ↑ P_{dias} (NOT proportional)
 ↑ P_{pulse} (bc improportional incr. of P_{syst} and P_{dias})
 ↑ P_{mean}
_{left graph young, right graph elderly}
Describe the effect of changed arterial compliance on the blood pressure.
When does it happen?
Relate it in a graph.
compliance decreases as people age, hence as elastin is successively replaced by collagen
→ incr. workload on left ventricle
 ↑ P_{syst}
 ↓ P_{dias}
 ↑↑ P_{pulse}
 constant P_{mean}
Describe the effect of changed blood volume on the blood pressure.
↑ blood volume → ↑ stroke volume (cf. own card)
Describe the effect of changed viscosity on the blood pressure.
↑ Ht → ↑ TPR (cf. own card)
Describe the effects of
 gender
 climate
on arterial blood pressure.
List other factors, too.

gender: estrogen → vasodilation → ↓ TPR

climate: heat → thermoregulation → ↓ TPR
 exercise
 sleep
 emotions
Describe the effect of gravity on large arteries, both in recumbent and upright position.
heart = reference level, zero height
95 mmHg in aorta
recumbent: no need to compensate hydrostatic pressure bc everything on heart level
 90 mmHg in head + feet (ΔP drives blood flow)
upright: Δh hearthead = 50 cm, and 130cm (feet)
 185 mmHg in feet (gravity → P added)
 53 mmHg in head (gravity → P substracted)
_{red curves}
Describe the effect of gravity on large veins, both in recumbent and upright position.
heart = reference level, zero height
2 mmHg in right atrium
recumbent: no need to compensate hydrostatic pressure bc everything on heart level
 5 mmHg in head + feet (ΔP drives blood flow)
upright: Δh hearthead = 50 cm, and 130cm (feet)
 100 mmHg in feet (gravity → P added)
 32 mmHg in head (gravity → P substracted)
_{blue curves}
Compare the effect of gravity on vascular beds in head and feet, both in recumbent and upright position.
different absolute pressures in head and feet
BUT: same ΔP driving pressure, 85 mmHg