How to describe LV Function? From fiber shortening to ... · Cardiac Function Cardiac...
Transcript of How to describe LV Function? From fiber shortening to ... · Cardiac Function Cardiac...
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EAE Teaching Course
How to describe LV Function?
From fiber shortening to ejection –
The physiology behind.
Sofia, Bulgaria, 5-7 April 2012
F.E. Rademakers
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Content
• Definition
• Anatomy
• Physiology
– Myofilaments
– Ventricle
– Stress - strain
– Pressure – volume
– Passive properties
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Cardiac Function
Cardiac ‘function’ is defined qualitatively:
The ability to work (pump) and keep on
working sufficiently.
=
Cardiac performance
Primary goal:
Maintain Cardiac Output
And Perfusion Pressure
by developing force in the wall to generate cavity pressure
and by deforming the wall to displace cavity volume
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J Am Coll Cardiol 2006;48:1988 –2001
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Fiber Architecture
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Fiber Architecture
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Am J Physiol Heart Circ Physiol 289: H1898–H1907, 2005;
Diastole Systole
DTMRI
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Transmural Fiber Distribution
Greenbaum et al. Br Heart J 1981
subendocardial
fibers
subepicardial
fibers
midwall
fibers
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Diffusion Tractography
Sosnovik , Circ CV Imaging 2009
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Fiber Architecture
•Laminar sheets
•Packed from base to
apex
•Branching
•4 cells thick
•Cleavage planes
•Tight coupling inside
sheets
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The myosin filament
Myofilaments
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Cardiac physiology
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Frank - Starling
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Cardiac Pump
W F and/or
Shortening Force
Fiber Ventricle
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Sarcomere Shortening
Epicardial
Ant
Post
AVO
Guccione et al 1997
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FILLING EMPTYING
ED volume x EF effective = stroke volume
distensibility/ contractility
compliance
active relaxation afterload x
atrial function preload
AV valve structure heart rate
pericardium
diastolic function systolic function
In Out
Ventricular Pump Performance
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LV Pressure and Volume
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Journal of Molecular and Cellular Cardiology 48 (2010) 851–858
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Load Dependence
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Deformation modes: What?
Longitudinal
shortening
Radial
thickening
Circumferential
shortening
+ Endocardial inward motion for ejection
Longitudinal
lengthening
Radial
thinning
Circumferential
lengthening
+ Endocardial outward motion for filling
+ Shearing (twisting,…) optimize
transmission of fiber force/deformation
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e = L – L0
L0
dimensionless
Strain: definition
Strain (e) = the deformation of an object expressed with
respect to its original shape
L
L0
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1D Lagrangian strain
1)()()(
)(00
0
00
L
tL
L
LtL
L
tdLt
L
Le
Lagrangian
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Strain Rate (e)
40% strain
1 s
40% strain
2 s
Average Lagrangian strain rate: 0.4 s-1 vs. 0.2 s-1
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2D strain
For a 2D object: 4 independent strains exist
4 independent strain rates exist
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Local cardiac coordinates
• Radial
• Longitudinal
• Circumferential
[ ] e
eRR eRC eRL
eCR eCC eCL
eLR eLC eLL
Facilitates physical interpretation and mathematics of the strain values (e.g. RR = wall thickening; CC/LL = circumferential/longitudinal shortening)
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Force
Two components to function
Ventricular ‘function’ Intrinsic ‘function’
Fiber mechanics
Regional
Myocardial mechanics
Bo
un
dary
co
nd
itio
ns
Interaction with
cardiovascular system
pressure/volume loading
- Venous return
- Valvular function
- Arterial impedance
- Fiber structure
- Tissue Elasticity
- Geometry
(thickness & shape)
Ventricular wall
- Segment Interaction
Deformation
Global
Pump performance
Wall stress
Wall deformation
shortening/lengthening
thickening/thinning
Ventricular Pressure
Ventricular Volume
Ejection/Filling
Fiber force
development
Myocyte Shortening
MVI/SRI
-Perfusion
-Activation
To understand the mechanics, we need to combine these two components
Stress
Strain
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Heng MK et al, Am Heart J 1985; 110: 84
Radius of curvature greater in septum
From echocardiography and cuff brachial BP in 9 subjects
Non-uniform systolic stress in the LV wall
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Stress-Strain
10
20
30
40
50
60
70
80
Reg
ion
al E
F
0 50 100 150 200 250 300 350 400 450
RCSN/THxSBP
NL
IDC
REF = 83.396 - .139 * RCSN/THxSBP; R^2 = .795 (NL)
REF = 57.377 - .094 * RCSN/THxSBP; R^2 = .606 (IDC)
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Strain Rate Load dependence
• Radial/Circumferential strain rate
Dependent on myocardial contractility
•Radial strain rate
Secondarily dependent on LVMV
-> increased LV mass – decreased radial LV function
=> Strain rate as reliable and valuable surrogate of true
ventricular contractility
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Ventricular performance
PRSW <-> EDP/EDV <-> Ea = ESP/SV
linear index of myocardial measure for preload measure for afterload
contractility
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Circulation 2010;121;2137-2145
Circled P’s indicate phosphorylatible sites.
Titin molecule
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Clinica Chimica Acta 375 (2007) 1–9
Stretching of the sarcomere from slack length (panel B) results in sequential extension of tandem Ig (panel C) and then PEVK and
N2B elements (panel C), each of which is responsible for a segment of the sarcomere length (SL)–passive force relation (right).
Shortening below slack length (panel A) results in reverse extension of titin with development of a restoring force
Stretching Titin
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Circulation 2010;121;2137-2145
Tuning Titin
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Summary
Ejection by
wall deformation
Systemic
resistance
AFTERLOAD
active force
development
within the fibres
1 cavity pressure
development
2
3
FIBRE ORIENTATION Fibre rearrangements
for optimal pressure built-up
(shape change during IVC)
15% FIBRE SHORTENING
TO 60% EJECTION FRACTION
GEOMETRY
shape, wall thickness
Volumes (preload)
TISSUE CHARACTERISTICS
e.g. ELASTICITY
(collagen matrix, titin)
SEGMENT INTERACTION
Glo
bal m
echan
ical bo
un
dary
con
ditio
ns
Reg
ion
al m
ech
anic
al b
ou
nd
ary c
on
dit
ions
Perfusion
Activation
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