Cardiac Output Flashcards
what measures the maximum tension (pressure) that can develop from a given LVEDV
- active curve
what measures the passive stretch (pressure or tension) on the ventricular myocytes as the heart is filled with blood
- passive curve
ventricular performance curves show the relationship between
- the EDV and SV
what would the heart being stimulated by epinephrine do to the cardiac performance curve?
- increase it
- move up
the amount of passive TENSION or stretch on the myocardial cells in the ventricles by the volume of blood in the ventricle just prior to contraction
- preload
what is preload proportional to
- LVEDV/P
- also proportional to the radius
- sarcomere length
relationship of preload to stroke volume
- increasing preload increases stroke volume
- can be seen in a graph
Central venous pressure determines
why?
- pressure in the right atrium and left atrium
- since they are in series
relationship of CVP to preload
- increasing CVP
- increases atrial pressure
- increases EDV/P or preload
main factors that influence CVP
- venous tone
- blood volume
- body position - gravity
- increased arteriolar dilation
the force or pressure the ventricle is working against after the onset of contraction
- measured by SVR
- afterload
- wall stress
relationship of afterload on SV
- increasing afterload decreases SV
what is afterload on the pressure/volume graph?
- the top sloped portion because it represents ejection
determinants of afterload
- systolic blood pressure
- aortic compliance
- aortic valve resistance
relationship between aortic compliance and afterload
example
- decreasing compliance increases afterload
- getting old
relationship between after load and pressure
- afterload is proportional to pressure
the contractile force that is developed by the ventricle at any given preload and afterload
- contractility (inotropy)
contractility proportional to
- how many actin-myosin cross bridges are made
- how much Ca2+ available per beat
relationship between contractility and SV
- increasing contractility increases SV
what happens if ventricular heart muscle increases the level of intracellular calcium per beat
- the myocytes contract more forcefully and with higher velocity
contractility on the pressure volume loop
- the slope of the active curve
what happens to active curve if we increase contractility
- moves up and to the left
effect of increasing contractility with same preload on SV
- increases SV
effect of decreasing preload with increased contractility on SV
- SV stays about the same
determinants of contractility
- intracellular Ca2+
- myosin ATPase activity
- ATP levels
- number of sarcomeres
40-90 bpm, decreasing HR affect on preload
- increases preload
90-170 bpm, effect on CO
- increases CO proportionately
180 bpm effect on CO
- decreases due to decreased filling time
preload determined by
- ventricular end diastolic tension
relationship between force and load
- load increases force
gravity affect on preload
- preload decreases when you stand up
sympathetic activity on preload
- increases tension of walls of veins and venules
myocardial oxygen demand proportional to
- stroke volume
- preload
afterload proportional to
- blood pressure and vascular stiffness
- SVR
cellular basis of afterload
- increasing afterload decreases velocity of myofibril shortening
- decreases velocity of systolic ejection
- decreases stroke volume
formula for afterload
P x r/ 2h
P = ventricular pressure r = ventricular radius h = ventricular wall thickness
effect of increasing afterload on oxygen demand
- increasing afterload will increase oxygen demand
effect of preload and afterload on contractility
- do not affect contractility
effect of calcium on slope of ventricular pressure
- more calcium available for contraction, the steeper the rise in ventricular pressure
formula for cardiac output
- stroke volume x heart rate
SVR (TPR) during exercise
affect on afterload
- decreases due to vasodilatation
- decreases afterload
