Muscle Physics & Heart as a Pump (complete) Flashcards
Define cardiac output
Volume of blood pumped per minute by left ventricle
What is the equation used for cardiac output?
CO = HR x SV
HR: heart rate
SV: stroke volume
Describe the changes in pressure through the cardiac cycle as a function of time
- After diastole & passive filling of LA, atrial contraction => increased atrial pressure => increased ventricular pressure (while mitral valve is open)
- When mitral valve closes, ventricular contraction starts => ventricular pressure ^ rapidly until it exceeds that in aorta => aortic valve opens
- Results in slow decrease in ventricular pressure => then faster drop in pressure once it’s below aortic pressure
- Ventricle continues to relax with both valves closed => pressure falls rapidly
Describe the changes in volume through the cardiac cycle as a function of time
- Ventricle passively fills => Atrium contract towards the end of diastole
- During isovolumetric contraction phase no ∆ in volume b/c aortic and mitral valves are closed
- aortic valve opens and blood leaves ventricle => volume decreases
What are the four phase of the cardiac cycle?
1) Filling phase
2) Isovolumetric contraction phase
3) Ejection phase
4) Isovolumetric relaxation phase
Describe the filling phase
- At end of diastole, LA has filled w/ blood from pulm vein
- Contraction triggered by electrical signal originating from SA node
- As LA starts to contract, atrial pressure ^ => no ∆ in volume
Describe the isovolumetric contraction phase
- As wave of depolarization reaches ventricle, it contracts and ventricular pressure ^
- This pushes mitral valve closed b/c pressure exceeds that in atrium
- Ventricular pressure increases rapidly b/c ventricle contracts but blood has no place to go
Describe the ejection phase
- As the ventricle contracts, ventricular pressure exceeds that in aorta => aortic valve opens, blood flow begins
- Decreased ventricular volume
- Increased and then decreases in ventricular pressure
Describe the isovolumetric relaxation phase
- As ventricle relaxes, pressure falls
- when ventricular pressure goes below aortic pressure => aortic valve closes
- Ventricles continues to relax => both valves closed, pressure falls rapidly (slowly at first)
- as ventricle relaxes, pressure eventually falls below that of atrium => mitral valve opens
- cycle begins again
Describe the Frank-Starling Law of the Heart
- Instrinsic mechanism by which the heart adapts to changes in preload
- Heart response to ^ EDV by increasing force of contraction
- Heart always functions on ascending limb ventricular function curve
Describe the PV loop diagram
Just go look at the ppt
Define stroke volume
SV = EDV - ESV
Define ejection fraction
Fraction of EDV ejected during systole
EF = SV/EDV = (EDV - ESV)/EDV
Define stroke work
- energy per beat (Joules)
- corresponds to area inside PV loop diagram
NOT the same for left and right sides of the heart
Define pulse pressure
End diastolic pressure - peak systolic pressure
Where are SV, EF, SW, and PP in the PV loop diagram?
GO LOOK AT THE PPT
Define preload
Pressure stretching the ventricle prior to contraction
Define afterload
resistance the LV must overcome to circulate blood
LV afterload: aortic pressure
Define contractility
- Inotropy
- Force of contraction that’s independent of fiber length
- describes systolic function of heart
- sympathetic tone is biggest factor affecting inotropy
- changes => new ventricular function
Reflects the strength of contraction at any given preload and afterload
Describe how altering preload, afterload, or contractility changes ventricular function
Increase in preload:
- results in ^ SV for next beat
- same ESV, EF ^
Increase in afterload:
- decrease in SV
- ventricle has to work harder against the increased aortic pressure => less blood ejected
- EDV unchanged, EF decreased, ESV increased
∆ in contractility:
- new starling curves
- corresponds to greater systolic pressure development
- Associated with ^ stroke risk
- ^ SV
Describe generally the systolic/diastolic pressure-volume relations and ventricular functions curves
- Pressure and volume changes in LV bound by 2 curves
1) systole pressure-volume relationship
2) end-diastolic pressure-volume relationship
Describe the end-diastolic pressure volume relationship
- Pressure-volume relationship during filling of heart BEFORE contraction
- Corresponds to passive elastic properties of ventricle
- Slope of EDPVR is shallow in normal physiological range
- represents PRELOAD on LV
Describe the systolic pressure volume relationship
- Curve at peak of isometric contraction
- Maximum pressure that can be developed for a given set of circumstances
- Steeper than EDPVR — pressure ^ a lot for small changes in volume
- Includes active plus passive properties
