Cardiovascular Performance Flashcards
What is preload in the normal heart?
Preload is the end-diastolic volume of the heart
What is the preload force?
The force applied to a muscle before the onset of contraction
What is the driving force of ventricular contraction?
It is the preload
What is the Frank Starling curve?
A graph that plots end-diastolic volume against ventricular pressure.
It has one convex curve on top representing peak systolic pressure and a concave sort of curve on the bottom representing end diastolic pressure. The area between the two is the strength of ventricular contraction which increases with volume
What principle is behind the preload being the driving force of ventricular contraction?
The length-tension relationship of muscle which shows that with an increase in length there is an increase in tension due to the increase of cross-bridges formed between the contractile muscle elements
What is CVP?
It is the pressure in the superior vena cava and is equivalent to the right atrial pressure and (in the absence of tricuspid valve disease) it is also equal to right ventricular end diastolic pressure
What is pulmonary artery wedge pressure?
It is equivalent to left atrial pressure and left ventricular end diastolic pressure in the absence of mitral valve disease
What is the equation for ventricular compliance?
Change in EDV/Change in EDP
How does compliance influence EDV?
If there is a decrease in compliance, the EDP will be overestimated
What is the change in EDP in diastolic heart failure?
Higher
What is the change in EDP in systolic heart failure?
High
What is the EDV in systolic heart failure?
High
What is the EDV in diastolic heart failure?
Low EDV (can’t distend to fill)
What is the EF in systolic heart failure?
Low
What is the EF is diastolic heart failure?
Normal
Where should the transducer be for an accurate CVP reading?
At the level of the right atrium (mid axillary line and fourth intercostal space supine)
Where is the level of the right atrium when a person is sitting up to 60 degrees?
5 cm below the sternal angle
When should CVP and wedge pressure be measured?
At the end of expiration
Why should CVP and wedge pressure be measured at the end of expiration?
Because that is when the intrathoracic pressure equals zero, so the measure of transmural pressure will be accurate since it is the difference between the intra vascular pressure and the intrathoracic pressure
What is the influence of intrathoracic pressure on CVP.
May cause a change in the measured pressure of the veins with respiratory variations but not in ventricular filling.
Take CVP at lowest point of tracing during ventilation
Take CVP at highest point with normal breathing
What does peep do to the cardiac filling pressures at end expiration?
Falsely elevates them because the intrathoracic pressure does not equal zero at the end of expiration
What is afterload?
The force applied to muscle after the onset of contraction
What is afterload in the normal heart?
The peak tension developed across the walls of the ventricles during systole
What is the law of Laplace?
Wall tension = pressure X radius / 2 X wall thickness
What are the components of afterload?
Preload
Pleural pressure
Vascular impedance
Peripheral vascular resistance
