pump 2 Flashcards
Frank Starling Law of the heart
- Heart always functions on the ascending limb of the ventricular function (Starling) curve.
- Heart responds to an increase in end diastolic volume (EDV) by increasing the force of contraction
- What comes in, must go out.
Molecular basis for Starling’s law
- Cardiac titin isoform is very stiff – resists stretch past a certain point.
- Ca2+ sensitivity of myofilaments increases at longer sarcomere lengths
- Longer sarcomere lengths change “lattice spacing” between actin and myosin, allows each cross bridge to generate more force.
Titin is
- Titin is a gigantic protein that spans Z-line to M-line in sarcomeres .
- “Molecular spring” that determines passive elasticity of muscle.
Skeletal muscle is more compliant due to
more elasticity in skeletal muscle titin isoform – can function on descending limb of length-tension relationship.
measures of cardiac performance
- blood pressure
- stroke volume
- ejection fraction
- stroke work
SV =
volume per beat
SV = EDV - ESV
typically 120-50 = 70 ml
ejection fraction (EF) =
proportion ejected at each beat
EF = SV/EDV EF = (EDV - ESV) / EDV = 70/120 =58%
stroke work =
energy per beat (in joules)
= area under curve
How do changes in Preload, Afterload, and Contractility independently affect cardiac performance?
Look at effects of stroke volume on next beat…
determinants of cardiac output?
- preload
- afterload
- inotropy
preload is the load/length to which a muscle is subjected before
shortening
factors that affect preload
- blood volume
- filling pressure & time
- resistance to filling
resistance to filling:
- right atrial pressure, AV valve stenosis
2. Ventricular compliance
what is the major determinant of preload
ventricular compliance
slope of EDPR is the inverse of
compliance
hypertrophy effect on compliance
reduces compliance
the steeper the slope, the harder it is for the ventricles to fill and the lower the EDV at any given EDP
dilation effect on compliance
dilation increases compliance
decreased compliance is
hypertrophy
increased compliance is
dilation
increased preload will cause
increase in SV on the next beat (via Starling’s law)
afterload is the load against which a muscle
contracts
factors that affect afterload
- Aortic pressure: hypertension increases afterload
- wall thickness
- radius
- Aortic stenosis
Afterload is strictly defined as
wall stress
major determinant of afterload is
aortic pressure
increased afterload causes a
decreased stroke volume in the next beat
inotrophy (contractility) is the
force of contraction independent of fiber length
inotropy describes the
systolic function of heart
what is the biggest affecting factor of inotropy
sympathetic tone
changes in inotropy describe
new ventricular function (starling) curves
increased inotropy will cause
increased in stroke volume on the next AND SUBSEQUENT beats
