4. Muscle Physics and Heart as a Pump Flashcards
What is the average resting CO?
5 L/min
What is the stroke volume?
the amount of blood pumped per beat
What is CO?
cardiac output: heart rate x stroke volume (the volume of blood pumped per minute by the heart)
How is CO controlled?
- heart rate (SA node, ANS and humoral agents)
2. stroke volume (preload, afterload, strength of contraction)
What sets the heart rate?
pacemaker cells in the SA node
What is the preload?
the venous return
What is afterload?
resistance to flow (aortic pressure)
What 2 things change the strength of contraction??
- length dependent regulation (Frank-Starling Law)
2. length independent regulation (via SNS)
What is the first phase of the cardiac cycle?
the filling phase
What occurs during the filling phase?
the mitral valve is open; volume high and pressure low
What is the second phase of the cardiac cycle?
the isovolumetric contraction phase
What happens during the isovolumetric contraction phase?
the aortic valve is closed; volume and pressure greatly increase, closing the mitral valve
What is the third phase in the cardiac cycle?
the ejection phase
What happens during the ejection phase?
blood leaves the ventricle- pressure is highest but volume reaches lowest
What is the fourth phase in the cardiac cycle?
isovolumetric relaxation phase
What happens during the isovolumetric relaxation phase?
the aortic valve closes; mitral valve closed
When does the mitral valve open?
at the beginning of the filling phase
What is the end diastolic curve?
the volumes and corresponding pressures during diastole
What does EDPVR stand for?
end diastolic pressure volume relationship
The EDPVR represents the _____ on the left ventricle.
preload
The EDPVR represents the preload on the _____.
left ventricle
What is the significance of Starling’s Law of the Heart?
what comes into the heart must be pumped out
Name various sources of resistance to filling.
- R atrial pressure
- AV valve stenosis
- ventricular compliance
What are the factors that affect preload?
- blood volume
- filling pressure and time
- resistance to filling
What does SVPR stand for?
Systolic pressure-volume relationship
Which is steeper- the SVPR or the EDPVR?
SVPR by a lot
What is the SVPR?
Maximum pressure that can be developed by the ventricle for a given set of circumstances
Violation of Starling’s law corresponds to?
heart failure
The heart responds to an increase in EDV by ____.
increasing the force of contraction
A healthy heart always functions on the ____ limb of the ventricular function curve.
ascending
Cardiac output MUST equal _____ and cardiac output from left and right ventricles MUST match.
venous return
What is the ESV?
end systolic volume- not zero! usually around 50 mL
