Preload and Afterload Flashcards
Define cardiac output.
Volume of blood each ventricle pumps per minute
What happens when RV output > LV output?
Pulmonary congestion would occur
What happens when LV output > RV output?
Pulmonary vessels would be emptied
What is preload?
Stretch of ventricular myocytes prior to contraction
What does end-diastolic volume indicate about preload?
Increased stretch increases contractile force so SV increases with increased EDV
What is the energy of contraction of a cardiac muscle fibre proportional to?
Intial fibre length at rest
Where does cardiac muscle normally operate?
Ascending phase of active tension-length relation
What is increased stretch associated with?
Increased Ca2+ sensitivity
Easier crossbridge formation
What is preload determined by?
central venous pressure
What 5 factors affect CVP?
Gravity
Blood volume
Skeletal muscle pump
Sympathetic nerves
Increased cardiac pumping
What does CVP determine?
Right ventricular EDV and SV of left ventricle
What is the effect of extracardiac pressure?
Reduce ventricular filling, SV and CO
What can cause extra cardiac pressure?
Disease of the pericardium
Define afterload.
Arterial pressures against which the ventricles pump
What is afterload influenced by?
Physical properties of arterial tree
Arterial blood volume
Peripheral vascular resistance
