Lecture 16: Ventricular function

Question 1

What happens to ventricular volume at the VE/IVR time period and why? (wiggers diagram)

Answer 1

Ventricular volume becomes negative as their is negative flow (backwards) because E aorta is less than E ventricle. (some back flow)

Question 2

How can the phases filling and ejection be divided in the wiggers diagram?

Answer 2

Into rapid and reduced time periods.

Question 3

What is the general difference between left and right ventricles in terms of pressures and valve sequences?

Answer 3

Pressure is lower in the right ventricle therefore timing is slightly different.

Question 4

Describe the timing of the mitral and tricuspid valves

Answer 4

The tricuspid valve opens before the mitral

The tricuspid valve closes after the mitral

i.e LV has less filling time

Question 5

Describe the timing of the aortic and pulmonary valve

Answer 5

The pulmonary valve opens before the aortic valve

The pulmonary valve closes after the aortic

i.e LV has less ejection time

Question 6

Why do the AV and semilunar valves have different timings between the left and right sides of the heart?

Answer 6

RV valves open sooner and close later because:

• Differences in electrical activation and pressures (takes less time to generate pressure in the RV.)

Question 7

Describe the pressure of the RA

Answer 7

~3mmHg

Question 8

Describe RV pressures

Answer 8

(s) 18mmHg

d) 0mmHg (i.v.r

Question 9

Describe PA pressures

Answer 9

(s) 18mmHg

(d) 12mmHg

Question 10

Describe PA wedge pressures (cap)

Answer 10

8mmHg average

Question 11

Describe LA pressures

Answer 11

8 mmHg average

Question 12

Describe LV pressures

Answer 12

(s) 130 mmHg

(d) 0 mmHg

Question 13

Describe the systemic aortic pressure

Answer 13

(s) 130 mmHg

(d) 75 mmHg

Question 14

Whats the components of CO?

Answer 14

CO = HR x SV

Question 15

What are the determinants of SV?

Answer 15

• Preload
• Afterload
• Inotropy

Question 16

How does HR affect CO?

Answer 16

HR directly influences CO and also indirectly acts via the determinants of SV particularly preload and inotropic state.

Question 17

Describe the main factors of CO;

Answer 17

CO = SV x HR

SV = EDV - ESV

EDV influenced by Preload
ESV influenced by Afterload and Inotropic state

HR influences preload and Inotropic state

Question 18

How does HR influence preload?

Answer 18

Reduced preload by reducing the time of ventricular filling therefore redoing SV

Question 19

How does HR influence inotropic state?

Answer 19

HR relates to the force frequency relationship that plays a minor role in ionotropy.

Question 20

What are the relavant graphs for ventricular performance?

Answer 20

PV loop
Ejection Fraction
Peak dP/dT
Ventricular function curve
CO/VR MRAP curve a.k.a guyton VP graph

Question 21

What does the linear line on the P-V graph represent?

Answer 21

Potential pressure of the chamber

This is never achieved as the valves open once threshold pressure is reached

Question 22

Potential pressure increases linearly with and represents what relationship?

Answer 22

EDV

This clearly reflects the force-sarcomere length relationship.

Question 23

When is the length tension relationship for sarcomeres exhibited?

Answer 23

During isometric or fixed length muscle contraction

Question 24

Why can sarcomeres generate varying levels of tension at a fixed resting length?

Answer 24

Inotropic state accounts for this and means that sarcomeres can generate more force from an unchanged resting length

Question 25

What can be obtained from a P-V loop?

Answer 25

The ventricular work performed each cardiac cycle (stroke work) SW = SV x TPR (P xV)

Question 26

What are the four determinants of cardiac performance?

Answer 26

Preload Afterload Inotropic state Chronotropic state

Question 27

What is preload?

Answer 27

The tension produced by the degree of stretch of myocyte filaments - L-T relationship - Length dependant activation (a) - Increased stretch increases troponin C sensitivity to Ca (b) - Increased stretch increases the activation of stretch sensitive Ca channels

Question 28

What is Afterload?

Answer 28

The pressure of which the ventricle must pump against Increased in hypertension.

Question 29

What is inotropic state?

Answer 29

The degree of activation of contractile proteins by Ca in the myocyte sarcomere.

Question 30

What influences inotropy?

Answer 30

- AP plateau phase (excitation contraction coupling) - External ion gradient (NCX and Na/K ATP ase transporters) - Force frequency relationship - ANS - Drugs \ Caffiene, inhibits PDE prevents cAMP breakdown \ Digoxin, cardiac glycoside inhibits Na/K ATPase, NCX reverses \ Verapamil, Ca channel inhibitor - Heart failure

Question 31

How does chonrotropic state influence CO?

Answer 31

- HR increases, CO increases - Force frequency relationship - High HR reduces SV, decreasing CO

Question 32

What does the equilibrium between CO and VR represent on the venous return/ CO curve?

Answer 32

This is the steady state equilibrium at which the heart works with some transient deviations. The MRAP at this point = mean systemic filling pressure

Question 33

What are normal values for Ejection Fraction?

Answer 33

``` Rest = ~50% Exercise = ~85% ```

Question 34

What are the two types of ventricular function curves?

Answer 34

Stroke volume vs preload | Stroke Work vs preload

Question 35

Why is stroke volume vs preload not used?

Answer 35

Stroke volume is difficult to measure and not independent of afterload

Question 36

Why is stroke work vs preload good?

Answer 36

Not susceptible to changes in after load LV EDP is used instead of EDV as it is easier to measure If MAP increases, SV decreases keeping SW constant.

Question 37

What does a ventricular function curve represent?

Answer 37

Summery of the P-V and frank-starling relations

Question 38

A family of curves on the ventricular function curve represents?

Answer 38

Different inotropic states

Question 39

What cardiac factors does a ventricular function curve account for?

Answer 39

Preload After load Inotropic state

Question 40

Describe how LA pressure is obtained?

Answer 40

A fluid filled catheter with a ballon tip is passed through the femoral vein via the heart into the PA. Ballon inflates and measures the pre-capillary pressure which is representative of the LA pressure mostly... This can measure both pulmonary artery pressure and pulmonary wedge pressure.

Question 41

Describe ventricular diastole:

Answer 41

- Begins with closure of the semilunar valves - Followed by isovolumetric relaxation (ends when atrial pressure exceeds that in the ventricle) - AV valves open and rapid ventricular filling occurs - This is followed by a phase of slow filling (Diastasis) - Atrial systole terminates ventricular diastole and the cycle begins again

Question 42

Generically describe the phases of the cardiac cycle:

Answer 42

1) Passive ventricular filling (diastole) 2) Isovolumic contraction (systole) 3) Ejection (Systole) 4) Isovolumic relaxation (diastole)

Question 43

What can be used as a measure of preload?

Answer 43

EDP

Question 44

Whats important regarding the heart when it comes to afterload?

Answer 44

Fibre tension and chamber geometry (law of laplace)

Question 45

Describe the law of laplace:

Answer 45

Wall stress (tension, T) = P*r / 2 x wall thickness

Question 46

Regarding the law of laplace what happens with increased preload?

Answer 46

- Increased preload = Inc. vol = Decreased wall thickness = Increased ventricular radius = Increased wall tension to generate the same pressure

Question 47

Regardin the law of laplace what happens with increased afterload?

Answer 47

Increased pressure needed thus the wall stress needs to be produced.

Question 48

What does increased inotropy do to the PV loop?

Answer 48

Increases the max potential pressure that can be generated thus the steepness increases.

Question 49

Check lecture PV loops

Answer 49

Now and add to this

Question 50

Whats the implication of the frank starling mechanism with two sides of the heart:

Answer 50

System is closed - Both sides must pump same volume over time - Hence changes must effect both L and R - Increased afterload leads to increased preload Arrhythmias impact balance

Question 51

Describe the the P-V relationship of the heart in response to increased afterload over one cardiac cycle;

Answer 51

Increased afterload in Aorta = - Decreased LV SV - The RV has continued pumping into pulmonary circuit, increased stretch of capacitence circuit increases pressure of flow into LV - LV EDV increases (preload) - SV increases Refer to diagram if need be note if EDV increases, the ventricle will not contract down to the same volume even if SV is increased

Question 52

How does dP/dT assess ventricular performance?

Answer 52

Max dP/dT used as indicator of contracility *Negative during relaxation

Question 53

What is stroke work? and its formula

Answer 53

The work done by the heart to eject blood SW = P x dV/dt Estimated by MAPxSV Stroke work is the area inside the PV loop, bottom wedge is the passive filling + Atrial contraction + inertia of ventricular filling (but is negligible)