Download (Microsoft PowerPoint - Dom_cir2_2016 [Kompatibilit\341si m\363d])

2016.12.01.
Cardiovascular Physiology II.
43. Hemodynamics: the functional categorization
of blood vessels.
44. The function of the aorta and the arteries.
Ferenc Domoki, November 28, 2016.
Blood vessels: elastic and
branching tubes
According to Hagen-Poiseuille’s law, length and
especially radius of vessels affect hydraulic
resistance greatly. In contrast to the criteria of the
law, the circulatory system consist of elastic,
branching, and not always cylindrical tubes= blood
vessels.
Because of vessel elasticity, increases in distending
blood pressure result also in increases in vessel
radius (reducing resistance), cross sectional area,
and volume.
Important concepts related to vascular elasticity:
transmural pressure, vascular compliance, critical
closing pressure, wall tension (Laplace’s law)
1
2016.12.01.
Transmural pressure: the
pressure distending the blood
vessel: Ptm=Pblood-Pinst
„transmural” : across the wall
The difference between the blood pressure
and the pressure outside the vessel wall
(interstitial pressure)
The interstitial pressure normally doesn’ t
play a significant role in determining
transmural pressure in the systemic arteries
(except in contracting muscle), but very
important in the low pressure system (venous
circulation)
VASCULAR COMPLIANCE: INCREASE IN VESSEL VOLUME IN RESPONSE TO UNIT
INCREASE IN PRESSURE. DEPENDS ON VESSEL DISTENSIBILITY AND SIZE.
Compliance: The slope of the vessel volume (V)transmural pressure (P) curve.
V
tgα=
∆V
∆P
Venous system
Arterial system
α
∆P
∆V
P
Transmural Pressure (mmHg)
VENOUS COMPLIANCE IS 20-24 TIMES LARGER THAN
ARTERIAL COMPLIANCE!!!
2
2016.12.01.
Blood vessels collapse, if the transmural
pressure falls below the critical closing pressure
value
Symp. inhibition
Critical closing pressure in
arteries is higher than the
mean vascular filling
pressure that develops after
Resting state
death (~7 mmHg).
Therefore, arteries collapse
after death, then fill up with
air once the dissection
begins. This misled scientists
Symp. stimulation for a thousand years
believing the arteries to
transport air (reflected in
their greek name, arteria
means windpipe) .
Laplace’s law
Wall tension = Transmural pressure x
r
T= Px h
T
P
Radius
Wall thickness
Tension of vessels: the tangential force in response to the distending
pressure. Wall tension is a force that would tear the vessel wall
Laplace’s law helps to identify which vessels are at risk
- veins – low (large radius -low blood pressure)
- capillaries – low (low blood pressure – small radius)
- arterioles – low (high pressure – small radius + thick wall)
- muscular arteries – low (high pressure – moderate radius +thick
wall)
-aorta/ large elastic arteries –high (high pressure – large radius –
relatively thin wall)
High blood pressure induced wall rupture is thus most likely in the aorta,
wall weakening causes aneurysm formation that sets off a vicious
circle. See next slide
3
2016.12.01.
Laplace’s law and Bernouilli’s law
explain the progression of aortic
aneurysms
TE = PE + KE + heat loss
Total energy of the blood =
potential energy (PE) + kinetic
energy (KE) + frictional heat
loss
Since Q=A·v, in the aneurysm
flow velocity decreases, so is
the kinetic energy component
decreased and the potential
(distending) component
increases.
As distension makes the
aneurysm grow, the decreasing
flow velocity increases the
distending pressure, that
increases the wall tension, that
increases diameter, that
decreases flow velocity, until…
Daniel Bernoulli (1700-1782)
8 great
mathematicians and
physicisists came
from this family
Daniel’s most
important finding:
when velocity
increases, pressure
decreases
4
2016.12.01.
Some good home experiments
to experience Bernouilli’s law
Ping-pong
balls
Air flow
How can the vascular resistance
be described in the branching
vasculature?
Vessels are connected to each other either in
series or in parallel.
The different organs in the systemic
circulation are connected in parallel
The vessels of the same class are also
connected in parallel (etc arteries, arterioles,
capillaries, veins)
Vessel classes are connected to each other in
series (arteries to arterioles, arterioles to
capillaries, capillaries to venules etc)
5
2016.12.01.
Compound resistance in
parallel connected tubes
Note that total resistance is
always smaller than the smallest
individual resistance!
Lung
Left heart
Right heart
coronaries
Brain
Muscle
Liver
GIS
Kidney
Skin
The organs of the
systemic circulation
are connected in
parallel
To describe these systems it
is easier to use conductance
instead of resistance
C = 1/R, Ctotal= 1/TPR
Ctotal=Ccoronaries+Cbrain +
Cmuscle +…
The figure shows the % of
total peripheral conductance
values in the systemic
circulation
The TPR is SMALLER than
ANY of the organ resistances
in the systemic circulation.
For instance, coronary
circulation has 5% of total
conductance that means that
its resistance
Rcoronaries=1/Ccoronaries=
1/0.05 Ctotal=20 TPR
6
2016.12.01.
Compound resistance of parallel
connected vascular segments
Rsegment=
R=1/C !!!
or
(
1
1 1
1
1
+ ....+
+ +
R1 R2 R3
Rn
)
Csegment= C1+C2+C3+C4+ …. Cn
Compound vascular resistance in each segment is
increasing by larger R (individual resistance), and by
smaller n (the number of parallel connected vessels).
Perhaps it is easier to see that segmental
conductance is smaller if individual conductances are
smaller and the number of parallel connected vessels
is smaller. Based on these principles the class of
arterioles possess the greatest resistance (large
individual R, relatively small n values)
Combined resistance of in
series connection
Rtotal= R1+ R2 + R3 + … Rn
TPR= Raorta + Rarteries + Rarterioles +
Rcapillaries + Rveins
Note that the total resistance is always
greater than the largest resistance!
7
2016.12.01.
Blood pressure/ segmental resistance in the circulation
TPR= Raorta + Rarteries + Rarterioles + Rcapillaries + Rveins
Rarterioles =∆Parterioles / Q (Q= cardiac output)
•Rarterioles >> Rcapilláries > Rveins > Rarteries > Raorta
•Blood pressure drop is greatest in the arterioles: this segment has the
largest vascular resistance, essentially determining the total peripheral
resistance (TPR).
• Control of arterial blood pressure and local blood flow is taking place in the
arterioles.
CLASSES OF VESSELS: STRUCTURE AND FUNCTION
Elastic
a.
Muscular Arteriole Capillary
a.
Precapillary
Venule
sphincter
Vein
Vena cava
Endoth.
Elast. t.
Smooth m
Conn. t
diameter
wall
25 mm
2 mm
4 mm
1 mm
30 µm
25 µm
8 µm 20 µm
1 µm
2 µm
5 mm
0.5 mm
30 mm
1.5 mm
Windkessel Distribution Resistance Exchange
Protein
Venous return
function:
&cell traffic
control
Continuous
Blood pressure &
Inflammation Cardiac output
flow
local flow control.
determination
8
2016.12.01.
CROSS SECTIONAL AREA AND VELOCITY OF FLOW
Cross sectional area
Veins
Capillaries
Arterioles
Elastic art.
cm² cm/s
Aorta
4 22.5
Arteries
20
Arterioles
40
Capillaries 2500 0.03
Venules
250
Veins
80
Vv. cavae
8 11.0
Muscular art.
Velocity
Q= A·v
DISTRIBUTION OF BLOOD VOLUME
Veins
Capillaries
Arterioles
Muscular art.
Heart
Aorta
Arteries
Arterioles
Capillaries
Veins
Pulmonary
circulation
%
7
6
6
2
6
64
9
Elastic art.
Depends on pressure and compliance,
most blood is in the venous system
9
2016.12.01.
Harvey’s book on the circulation, the
beginning of modern medicine
William Harvey
(1578 – 1657)
Exercitatio Anatomica de
Motu Cordis et Sanguinis (in Animalibus)
(1628)
THE ARTERIAL SYSTEM
Starling’
Heart-lung
preparation
TPR
Venous reserve
LUNG
aorta pressure
Ventricular volume
Atrial pressure
10
2016.12.01.
THE WINDKESSEL FUNCTION
FLOW
PRESSURE
push
No windkessel
Push-Pull
pull
Push-Pull
Airtank = Windkessel
push
With windkessel
pull
Push-Pull
Push-Pull
Windkessel function of elastic
arteries
During ventricular ejection,
the distended aorta store
blood and energy of the
contraction.
During diastole, the aorta
passively contracts and
pushes blood forward
toward the periphery.
11
2016.12.01.
ARTERIAL BLOOD PRESSURE
(MABP)
MABP ≈ Pd + 1/3(Ps - Pd)
Pulse pressure= Systolic pressure- Diastolic
pressure
AGE-DEPENDENT INCREASE IN ARTERIAL
BLOOD PRESSURE
male female
4y
88/60 88/60
20 y 118/71 118/70
40 y 126/77 131/81
50 y 150/88 156/90
Primarily the systolic pressure increases with age.
12
2016.12.01.
AGING DECREASES AORTIC ELASTICITY
Compliance decreases in the higher blood pressure range.
FACTORS AFFECTING SYSTOLIC AND
DIASTOLIC BLOOD PRESSURE
• Stroke volume
• Elasticity of the aorta
• Total peripheral resistance (TPR)
13
2016.12.01.
EFFECT OF STROKE VOLUME INCREASE ON ARTERIAL
BLOOD PRESSURE
VS2
VD2
VS1
• PS strongly increase.
• PD moderately increases.
•Pulse pressure increases.
VD1
PD1 PS1 PD2
PS2
EFFECT OF REDUCED AORTIC ELASTICITY ON
ARTERIAL BLOOD PRESSURE
Elastic (young) aorta
VS1
Rigid (old) aorta
VD1
PD2 PD1 PS1PS2
• Systolic pressure (PS) increases.
• Diastolic pressure (PD) decreases.
•Pulse pressure greatly increases.
14
2016.12.01.
EFFECT OF TPR ON ARTERIAL BLOOD PRESSURE
increased TPR
increased TPR + decreased
elasticity
VS2
VD2
VS1
VD1
PD1 PS1
PD2 PS2
PD1 PS1
PD2
PS2
• PS significantly increases • PS greatly increases
• PD significantly increases • PD significantly increases
SUMMARY OF ARTERIAL BLOOD PRESSURE CHANGES
baseline
120
80
Stroke volume increased
140 Hgmm
90
reduced compliance
120
80
120
80
120
80
baseline
140 Hgmm
60
increased TPR
150 Hgmm
110
increased TPR +
decreased compliance
180 Hgmm
110
change
15
2016.12.01.
FLOW VELOCITY AND PROPAGATION OF PRESSURE PULSE
DISTANCE OF BALL MOVEMENT= X
DISTANCE OF PRESSURE PULSE MOVEMENT: Y
The propagation velocity of the pressure pulse (Y/t) is much
faster, than the velocity of blood flow (X/t).
PROPAGATION OF PRESSURE PULSE
• Propagation velocity
- in the aorta: 3-5 m/s;
- in little arteries: 15-30 m/s.
• Mean flow velocity is ~20-30 cm/s in the aorta and
decreases toward the periphery.
• Velocity of pulse pressure propagation is increased by:
- decreased wall elasticity
- increasing wall thickness
16
2016.12.01.
PRESSURE PULSE AND FLOW PULSE
Pressure pulse increases toward the periphery.
Flow pulse decreases toward the periphery.
CHANGE IN THE PRESSURE PULSE SHAPE DURING PROPAGATION
Towards the periphery:
• Systolic peak increases
• incisura disappears
• diastolic peak appears
• time lag
Causes of changes
• Damping
• interference with
reflected waves
• pressure-dependent
propagation
17
2016.12.01.
The arterial pulse
The pressure changes in the aorta
during the cardiac cycle are transmitted
along the arteries as a pressure pulse creating a volume pulse that can be
palpated by pressing the arteries
against a flat hard surface
the pulse depends on the function of
BOTH the heart and the transmitting
arteries!
Palpation sites
18
2016.12.01.
Arterial pulse qualities (in
Latin)
pulsus frequens
pulsus altus
pulsus celer
pulsus durus
pulsus regularis
pulsus aequalis
pulsus rarus (rate)
pulsus parvus (amplitude)
pulsus tardus (rate of rise)
pulsus mollis (strength)
pulsus irregularis
(rhythmicity)
pulsus inaequalis (similarity)
Arterial Pulse: examples
Pulsus irregularis et inaequalis =
arrhythmia absoluta
Pulsus celer et altus
Pulsus frequens, parvus et mollis
= pulsus filiformis
19