Download Venous return

Applied physiology II.
Circulation, haemodynamic
support
Rudas László
University of Szeged
Department of Anaesthesiology and Intensive Care
Medical ICU
The cardiovascular system provides appropriate
oxygen and energy supply, via appropriate local
circulation to the tissues.
Circulation consists
microcirculation
of
macrocirculation
and
Normal circulation requires:
a pump, blood vessels, and normal blood
volume
The „Pump”
Say kids!
What does the
heart generate?
Flow
?
Pressure
?
Both !
Contractility
Pressure
contractility
Stroke volume
The role of contractility
Arterial pressure
contraktility
Stroke volume
elastance
Arterial pressure
Arterial elastance
elastance
Stroke volume
Arterial pressure
Heart - circulation coupling
contractility
elastance
Stroke volume
Coupling Systems
Circulation
Heart
A different view,
(a different representation)
of the „Pump”
Left ventricular pressure
End-systolic
Pressure-volume relationship
End-diastolic
Pressure-volume relationship
Ejection
Isometric
contraction
Isometric
relaxation
Ventricular filling
Left ventricular volume
Sympathetic activation
Left ventricular pressure
End-systolic
Pressure-volume relationship
End-diastolic
Pressure-volume relationship
Ejection
Isometric
contraction
Isometric
relaxation
Ventricular filling
Left ventricular volume
Dyastolic function is dependent on both
normal active relaxation, and passive
distensibility.
Left ventricular pressure
End-systolic
Pressure-volume relationship
Systolic dysfunction
End-diastolic
Pressure-volume relationship
Ejection
Isometric
contraction
Isometric
relaxation
Ventricular filling
Left ventricular volume
Left ventricular pressure
End-systolic
Pressure-volume relationship
Diastolic dysfunction
Ejection
Isometric
contraction
End-diastolic
Pressure-volume
relationship
Isometric
relaxation
Ventricular filling
Left ventricular volume
The „Pump” and the
concept of „preload”
The role of the end-diastolic volume
contractility
Arterial pressure
elastance
Stroke volume
Cardiac function curve
Cardiac outpul (l/min)
20
15
10
5
the good old Starling curve
0
4
8
Right atrial pressure (mmHg)
12
The preload of a muscle strip
Active tension (g)
8
4
0
0
2
Length increase (mm)
4
LaPlace formula
For thick walled spheres
=PR/2w
w=wall thickness
P=pressure
R=radius
The preload is the wall stress of the
ventricle prior to ejection.
Clinically it is characterized by the
ventricular end-diastolic volume, and/or
ventricular end-diastolic pressure.
Left ventricular pressure
The role of the end-diastolic volume
End-systolic
Pressure-volume
relationship
Ejection
Isometric
contraction
Isometric
relaxation
End-diastolic
Pressure-volume
relationship
Ventricular filling
Left ventricular volume
Left ventricular pressure
The markers of the preload
End-diastolic
pressures
End-diastolic
volume
The markers of the preload
Left ventricular pressure
Which marker is more reliable ??
End-diastolic
pressures
End-diastolic
volume
Factors to be considered:
1. The end-diastolic pressure-volume relationship is curvilinear.
above a certain point monimal volum cshange is mirrored by considerable
pressure elevation. The slope of the relatiomship changes from subject to subject
2. The left vantricular diastolic function is very sensitive to ischemia, and injury.
Thus end-diastolic pressure may rise without volume change.
End-diastolic
pressures
End-diastolic
volume
Lichtwarck-Aschoff et al. Intensive Care Med1992; 18:142-147
Factors to be considered:
1. The end-diastolic pressure-volume relationship is curvilinear.
above a certain point monimal volum cshange is mirrored by considerable
pressure elevation. The slope of the relatiomship changes from subject to subject
2. The left vantricular diastolic function is very sensitive to ischemia, and injury.
Thus end-diastolic pressure may rise without volume change.
3. End-diastolic pressure may be influenced by the fact, that left and right heart share
location within the pericardial space. Dilation of the right ventricle, or pericardial fluid
accumulation may also increases EDP.
End-diastolic
pressures
End-diastolic
volume
Watch out for that kitty !!!
The vasculature
Vascular compliance
Volume


V
P
pressure
Compliance
Relatíve volume
4
3
2
1
AORTA
VENA CAVA
0
0
80
160
240
320
0
8
16
pressure (cm water)
24
Intravascular
pressures
Factors to be considered:
1. Vessels could be considered as conduits, connecting the heart
to the periphery.
2 Vessels, however are also elastic „containers”, and their capacity
to blood is determined by their distending pressure.
3 Pressure could be generated by blood flowing through the tubes.
4 Certain amount of pressure could be also generated by
„overstretching” the vessels,
5 The distensibility and the resistance characteristics of the
vessels differ tremendously at different sites of the circulation
Arterial pressure
generation
The „Ohmic” resistance
Cardiac output
Cardiac output 2
Cardiac output 1
300
P1
P2
Arterial pressure
Generated flow
= cardial output (CO)
Generated pressure = mean art. pressure (MAP)– right atrial pressure (RAP)
Systemic Vascular
Resistance (SVR
= (MAP-RAP)/CO
dimension: Hgmm/l/min
SVR index (SVRI)
=
dimension: Hgmm/l/min/m2
(MAP-RAP)/CI
The „overstretching” of the
vessels:
I. With „arrested circulation”
During circulatory arrest theblood volume
distrbute according to the distensibility of
the various vascular compartments, and
will exert a steady pressure on the walls.
That pressure is the mean vascular filling
pressure
Venous Capacity
100
Blood
Volume
% of control
 3.5 l (50 ml/kg) „unstressed volume”
0
0
5
10
15
20
Pms
Rothe et al. Arch Intern Med 146:977-82, 1986
Venous Capacity
Sympathetic blockade
100
Blood
Volume
% of control
Noradrenalin
0
0
5
10
15
20
Pms
Rothe et al. Arch Intern Med 146:977-82, 1986
Venous Capacity
Sympathetic blockad
Noradrenalin
100
Blood
Volume
% of control
Reflex compensation range:
15-20 ml/kg  1-1.5 l blood
0
0
5
10
15
20
Pms
Rothe et al. Arch Intern Med 146:977-82, 1986
Mean systemic filling pressure
During circulatory arrest theblood volume
distrbute according to the distensibility of
the various vascular compartments, and
will exert a steady pressure on the walls.
That pressure is the mean vascular filling
pressure
Circulatory arrest
Intact circulation
During circulatory arrest the heart itself will distend as well.
(The heart ismuch more compliant, than the arterial system).
The distension of the heart however is not proportional,
(The right heart is much more complient than the left)
Changes in ventricular volumes following arrest
Cardiac arrest: MRI series
Chamberlain D et al. Resuscitation 2008;77:10-15
Mean systemic filling pressure is the
prevailing
capillary
pressure
end,
in
at
the
normal
conditions it is around 8 mmHg.
venus
basline
The „overstretching” of the
vessels:
II. With increasing cardiac
output
„compliant ér”
„noncompliant ér”
How this applies
to the total circulation ?
Circulatory arrest
Increasing CO
When generating cardiac output, the heart
Translocate blood from the venous compartment
To the arterial compartment
Circulatory arrest
Increasing CO
Questions of venous return
- Peripheral passive regulation
Effect of Sympathetic Tone on AutoTransfusion from Splanchnic Region
Splanc ni Blood Flow (m /min)
Arterial Outflow Restriction
VenousOutflow
300
200
Arterial Inflow
45 ml
100
0
10
20
Time (seconds)
Questions of venous return
- Peripheral active regulation
Effect of Sympathetic Tone on AutoTransfusion from Splanchnic Region
Splanc ni Blood Flow (m /min)
Arterial Outflow Restriction
Splanchnic Nerve Stimulation
Venous Outflow
300
200
Arterial Inflow
45 ml
100
0
10
71 ml
20
0
Time (seconds)
10
Questions of venous return
- Return to the heart
Venous return
Venous return curve
0
10
Right atrial pressure
Influence of negative intrathoracic pressure
on right atrial
and systemic venous drainage
DSA image
normal inspiration
DSA image
„Müller manoeuvre”
-40 Hgmm
Virolainen J. Eur Heart J 1995;16:1293-1299.
Cardiac output (L/min)
Venous return (l/min)
Right atrial pressure (mmHg)
Right atrial pressure (mmHg)
Apart from temporary fluctuations,
cardiac output and
venous return should be equal.
Venous return (l/min)
/Cardiac output (L/min)
The Guyton diagram
Right atrial pressure (mmHg)
Venous return (l/min)
/Cardiac output (L/min)
The Guyton diagram
Right atrial pressure (mmHg)
Cardiac function
- systolic function
contractility
preaload
afterload
heart rate
- diastolic function
structure of the myocardium
Questions of venous return
-Does the pump function
Influence venous return?
Cardiac output and right atrial pressure in pacemaker dependent dogs
Sheriff DD és Mendoza JR. Exerc Sport Sci Rev 2004;32:31-35
Pacemaker dependens alanyok perctérfogat és RAP összefüggései
Sheriff DD és Mendoza JR. Exerc Sport Sci Rev 2004;32:31-35
Pacemaker dependens alanyok perctérfogat és RAP összefüggései
Sheriff DD és Mendoza JR. Exerc Sport Sci Rev 2004;32:31-35
Circulatory arrest
Increasing CO
Questions
of the „afterload”
The afterload is the wall stress of the
ejecting ventricle.
Clinically it is characterized by the
ventricular pressure generated during
ejection.
(it
is
certainly
an
oversimplification).
myocardial wall stress during systolic ejection
afterload
ventricular
systolic radius
ventricular
systolic pressure
myocardial
wall thickness
end diastolic radius
output impedance
normal growth, hypertrophy
systemic arterial pressure
diastolic pressure
systolic pressure
blood volume
total peripheral resistance
outflow tract resistance
vascular resistance
obstructive CMP
pulse pressure
stroke volume
arterial compliance
Norton, Advances in Physiology Education 2001;25:53-61
The abnormal distensibility of ther
conductance vessels (i.e. increased
stiffness),
contributes
to
the
increased central arterial pressure
during ejection.
Left ventricular pressure
Left ventricular pressure
„Afterload mismatch”: a relative term
Left ventricular volume
Left ventricular volume
Everybody in the room
who knows 3 ways to increase
Cardiac output raise hand !!
Types of circulatory failure
- a szív csökkent pumpafunkciója - cardiogenic shock
- reduced venous return - hypovolaemic shock
- csökkent artériás tónus a véráramlás abnormális
eloszlásával - distributive shock
- outflow obstruction - obstructive shock
Let’s put the puzzle together
(start with normal parameters)
In order to put the puzzle together, I had to
change
the directions of the axes
of certain traditional diagrams.
Do not panick!
Systemic vascular resistance
Cardiac output
Cardiac output 1
Cardiac output 2
Arterial pressure
300
Venous return
Venous return curve
10
Right atrial pressure
Cardiac output /
Venous return
Systemic vascular resistance
Venous return curve
Cardiac output 1
Cardiac output 2
Arterial pressure
300
Right atrial pressure
10
Apart from temporary fluctuations, cardiac output and
venous return should be equal.
300
Arterial pressure
Arterial compliance curve
Arterial
volume
10
Pressure in the great veins
Venous compliance curve
Venous
volume
Cardiac output /
Venous return
2. Systemic vascular resistance
1. Venous return curve
Cardiac output 2
Cardiac output 1
Arterial pressure
Right atrial pressure
300
10
artériás
Arterial
volume
3. Arterial compliance curve
vénás
Venous
volume
4. Venous compliance curve
Cardiac output /
Venous return
2. Systemic vascular resistance
1. Venous return curve
Cardiac output 2
Cardiac output 1
Arterial pressure
Right atrial pressure
300
10
artériás
Arterial
volume
3. Arterial compliance curve
vénás
Venous
volume
4. Venous compliance curve
Mechanisms of failure
Mechanisms of failure
Low cardiac output
Cardiac output /
Venous return
Systemic vascular resistance
Venous return curve
Cardiac output
Arterial pressure
Right atrial pressure
300
10
artériás
Arterial
volume
Arterial compliance curve
vénás
Venous
volume
Venous compliance curve
Therapy ?
Limitations of the therapy ?
Mechanisms of failure
Decreased venous return
- hypovolemia
Cardiac output /
Venous return
Systemic vascular resistance
Venous return curve
Cardiac output 2
Arterial pressure
Right atrial pressure
300
10
vénás
Arterial
volume
Arterial compliance curve
Venous
volume
Venous compliance curve
Cardiac output /
Venous return
Systemic vascular resistance
Venous return curve
Cardiac output 2
Secunder systolic dysfunction
Arterial pressure
Right atrial pressure
300
10
vénás
Arterial
volume
Arterial compliance curve
Venous
volume
Venous compliance curve
Therapy ?
Limitations of the therapy ?
Mechanisms of failure
Loss of
vascular resistance
Cardiac output /
Venous return
Systemic vascular resistance
Arterial pressure
. Venous return curve
Right atrial pressure
300
10
artériás
Arterial
volume
Arterial compliance curve
vénás
Venous
volume
Venous compliance curve
Therapy ?
Diastolic heart failure is suspected in cases
where clinical signs of decompensation are
present, in spite of preserved systolic
function (EF≥50%).
(The diagnosis could be further confirmed by
echocardiography).
myocardial end-diastolic wall stress
preload
end-diastolic
radius
end-diastolic
filling pressure
compliance of
ventricle and
pericardium
total blood volume
blood volume distribution
venous compliance
venous return
myocardial wall
thickness
normal growth
hypertrophy
Norton, Advances in Physiology Education 2001;25:53-61