Lecture 2: Cardiac and Vascular Function: Flashcards
Wiggers Diagram
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What happens to ventricular volume at the VE/IVR time period and why?
Ventricular volume becomes negative as their is negative flow (backwards) because E aorta is less than E ventricle. (some back flow)
How can the phases filling and ejection be divided in the wiggers diagram?
Into rapid and reduced time periods.
What does an echocardiogram show in terms of ventricular wall thickness during the cardiac cycle?
Ventricular wall thickness varies between systole and diastole.
What sort of motion do the atrioventricular valves reform during ejection?
A ripple like effect as blood is ejected.
What is the general difference between left and right ventricles in terms of pressures and valve sequences?
Pressure is lower in the right ventricle therefore timing is slightly different.
What does the RV pump blood through?
The low resistance lungs
What does the LV pump blood through?
The entire system circuit
Describe the timing of the mitral and tricuspid valves
The tricuspid valve opens before the mitral
The mitral valve closes just before the mitral valve
i.e LV has less filling time
Describe the timing of the aortic and pulmonary valve
The pulmonary valve opens before the aortic valve
Aortic closes before the pulmonary valve
i.e LV has less ejection time
Why do the AV and semilunar valves have different timings between the left and right sides of the heart?
RV valves open sooner and close later because:
- Differences in electrical activation and pressures (takes less time to generate pressure in the RV.)
Describe the pressure of the RA
~3mmHg
Describe RV pressures
(s) 18mmHg
d) 0mmHg (i.v.r
Describe PA pressures
(s) 18mmHg
(d) 12mmHg
Describe PA wedge pressures (cap)
8mmHg average
Describe LA pressures
8 mmHg average
Describe LV pressures
(s) 130 mmHg
(d) 0 mmHg
Describe the systemic aortic pressure
(s) 130 mmHg
(d) 75 mmHg
Whats the components of CO?
CO = HR x SV
What are the determinants of SV?
- Preload
- Afterload
- Ionotropy
How does HR affect CO?
HR directly influences CO and also indirectly acts via the determinants of SV particularly preload and inotropic state.
Describe the main factors of CO;
CO = SV x HR
SV = EDV - ESV
EDV influenced by Preload
ESV influenced by Afterload and Inotropic state
HR influences preload and Inotropic state
How does HR influence preload?
Reduced preload by reducing the time of ventricular filling therefore redoing SV
How does HR influence inotropic star?
HR relates to the force frequency relationship that plays a minor role in ionotropy.
What are the relaxants graphs for ventricular performance?
PV loop Ejection Fraction Peak dP/dT Ventricular function curve CO/VR MRAP curve a.k.a guyton VP graph
What does the linear line on the P-V graph represent?
Potential pressure of the chamber
This is never achieved as the valves open once threshold pressure is reached
Potential pressure increases linearly with and represents what relationship?
EDV
This clearly reflects the force-sarcomere length relationship.
When is the length tension relationship for sarcomeres exhibited?
During isometric or fixed length muscle contraction
Why can sarcomeres generate varying levels of tension at a fixed resting length?
Inotropic state accounts for this and means that sarcomeres can generate more force from an unchanged resting length
What can be obtained from a P-V loop?
The ventricular work performed each cardiac cycle (stroke work)
SW = SV x TPR (P xV)
What are the four determinants of cardiac performance?
Preload
Afterload
Inotropic state
Chronotropic state
What is preload?
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
What is Afterload?
The pressure of which the ventricle must pump against
Increased in hypertension.
What is inotropic state?
The degree of activation of contractile proteins by Ca in the myocyte sarcomere.
What influences ionotropy?
- 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
How does chonrotropic state influence CO?
- HR increases, CO increases
- Force frequency relationship
- High HR reduces SV, decreasing CO
What does the equilibrium between CO and VR represent on the venous return/ CO curve?
This is the steady state equilibrium at which the heart works with some transient deviations.
The MRAP at this point = mean systemic filling pressure
What are normal values for Ejection Fraction?
Rest = ~50% Exercise = ~85%
What are the two types of ventricular function curves?
Stroke volume vs preload
Stroke Work vs preload
Why is stroke volume vs preload not used?
Stroke volume is difficult to measure and not independent of afterload
Why is stroke work vs preload good?
Not susceptible to changes in after load
If MAP increases, SV decreases keeping SW constant.
What does a ventricular function curve represent?
Summery of the P-V and frank-starling relations
A family of curves on the ventricular function curve represents?
Different inotropic states
What does a ventricular function curve account for?
Preload
After load
Inotropic state
Describe how LA pressure is obtained?
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.
What are two methods of CO measurement?
Ficks Method
Thermodilution
What is Ficks method?
Based on conservation of mass.
Using a known quantity of bolus i.e O2 injected prior to the heart and over time the concentration is measured down stream. The rate of dilution is representative of CO
What are the prerequisite of ficks method?
1) Mixed venous blood (whole body average of O2 concentration
2) All the measured substance must be collected, none lost
3) Steady state must exist, Ventilation and CO
What is thermodilution?
Using this indicator dilution technique.
- Cold saline is used as indicator
- Measured downstream temperature change to indicate the rate of dilution and thus CO
What are the advantages of thermodilution?
- No arterial puncture needed
- No toxicity
- Recirculation is negligible / ignored
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