Ventricular Pump Function

1
Ventricular Pump Function

• Anatomy
• Ventricular Pump Function
• Resting Myocardial Mechanics
• Constitutive equations for passive myocardium
• Regional Wall Stress and Strain

2
Cardiac Anatomy
Mitral
Aorta
SVC
Pulmonary artery
Pulmonic
Tricuspid valves
Base
LA
RA
LV
RV
Septum
Epicardium
Endocardium
Apex
3
Ventricular Geometry
Prolate Spheroidal Coordinates
Truncated ellipses of revolution
x1 d coshl cosm x2 d sinhl sinm cosq x3 d
sinhl sinm sinq
4
Ventricular Dimensions
5
Ventricular Scaling
Allometric relation between heart mass MH (g) and
body mass, M (kg)
MH kMa
Combined species k 5.8 a 0.98 ? 1.0 ? MH/M ?
5.8 g.kg-1 Mature rabbits and rats MH/M ? 2
g/kg Adult humans MH/M ? 5 g/kg Horses and
dogs MH/M ? 8 g/kg
6
Fiber and Sheet Architecture
x510
7
The Cardiac Cycle
2
1
3
4b
4a
Systole 1. Isovolumic contraction 2. Ejection Di
astole 3. Isovolumic relaxation 4. Filling a)
Early, rapid b) Late, diastasis
4a
4b
1
3
2
8
Conduction System
9
CoronarySystem
10
Pressureand Volume
11
The Pressure-Volume Diagram
End-systole (ES)
2
0
SVEDV-ESV Ejection Fraction EFSV/EDV
Ejection
1
6
AVC
AVO
1
2
Pressure (kPa)
Stroke volume (SV)
Isovolumic contraction
Isovolumic relaxation
8
End-diastole (ED)
4
Filling
MVO
MVC
0

2
0
0

1
5
0

1
0
0

5
0
0

Volume (ml)
12
The Pressure-Volume Diagram
2
0
Ejection
1
6
AVC
AVO
1
2
Pressure (kPa)
Stroke (external) work
Isovolumic contraction
Isovolumic relaxation
8
4
Filling
MVO
MVC
0

2
0
0

1
5
0

1
0
0

5
0
0

Volume (ml)
13
Preload and Afterload
2
0
ESPVR
1
6
control
1
2
Pressure (kPa)
? preload
8
EDPVR
? afterload
4
0

2
0
0

1
5
0

1
0
0

5
0
0

Volume (ml)
14
Starlings Law of the Heart(The Frank-Starling
Mechanism)
increased contractility (e.g. adrenergic agonist)
decreased contractility (e.g. heart failure)
Stroke work
Preload (EDV or EDP)
15
Contractility (Inotropic State)
increased contractility (e.g. adrenergic agonist)
2
0
ESPVR
decreased contractility (e.g. heart failure)
1
6
1
2
Pressure (kPa)
8
EDPVR
4
0

2
0
0

1
5
0

1
0
0

5
0
0

Volume (ml)
16
Time-Varying Elastance
P(t) E(t)V(t) - V0
17
Physiological Basis of Starlings Law
2
0
ESPVR
1
6
1
2
Pressure (kPa)
8
EDPVR
4
0

2
0
0

1
5
0

1
0
0

5
0
0

Volume (ml)
18
Ventricular Function Summary of Key Points

• Ventricular geometry is 3-D and complex
• Ventricular shape is similar across mammalian
  species and prolate spheroidal coordinates
  provide a useful approximation
• Fiber angles vary smoothly across the wall
• Systole consists of isovolumic contraction and
  ejection diastole consists of isovolumic
  relaxation and filling
• Area of the pressure-volume loop is ventricular
  stroke work which increases with filling
  (Starlings Law)
• Ventricles behave like time-varying elastances
• The slope of the end-systolic pressure volume
  relation is a load-independent measure of
  contractility or inotropic state.