Cardiac Muscle Mechanics Flashcards
SV can increase put to abut
50%
HR can increase to a max. Of approx. _____ your age
220
Increases in _____ alone decreases the duration of diastole
Heart rate
Decreasing the duration of diastole decreases the
Ventricular filling and thus could decrease SV
SV increases or decreases during exercise
Increases
SV= EDV - ESV
What are the factors that regulate SV?
EDV- preload
ESV- afterload and inotropy
Wall stretch is max. At the
End of diastolic vol. (EDV) or end diastolic pressure (EDP)
Increases in either EDV or EDP _________ the sarcomeres and increases the
EDP stretches the sarcomeres and thus increases the force of the next contraction
Preload (2) meaning
- Initial stretching of the cardiac myocytes prior to contraction
- Average ventricular sarcomeres length at the end of diastole
Length tension curve shows that
Increasing the length (sarcomeres stretch) results in increasing the contractile force
Increases in EDV produced ______ in contractile force
Increases
OTTO frank on experiments on intact hearts was the study
Of the effects of diastolic stretch on contraction
Increased filling pressure leads to ________ EDV or EDP resulting in
Increase in EDV or EDP resulting in an increased SV at a constant aortic pressure
Frank starling law of the heart
The greater the volume of blood entering the heart during diastole the greater the volume of blood ejected during systolic contraction
Increased EDP or EDV results from increasing
Venous return to the heart
Stretching a resting cardiac fiber causes an immediate rise in
Contractile force in the very next contraction
Contractile force is the same as
SV
With ____, the sarcomeres length allow for more optimal cross-bridge formation
Stretch
True or false:
Too much stretch or too much contraction can lead to poor functioning sarcomeres and thus inefficient contraction force
Yep
Stretching the myofibers increases the
Affinity of troop in C for Ca2+
At longer sarcomeres length, Ca2+ activates more or less thin filaments at physiological concentrations
More
Compliance if the ratio of
Volume change to pressure change
All ventricles exhibit increasing stiffness (deceasing compliance) at higher/lower volumes
Higher
Ventricular hypetrophy _________ compliance and ________ volume in ventricle at a given EDP leading to a _________ in sarcomeres stretch
Decreased compliance and decrease in volume leading to a decrease in sarcomere stretch
Preload affected by compliance changes?
Yep
Dilation of ventricle due to chronic volume overload leads to a _______ compliance and allows for a _____ EDV at a lower EDP with stretched sarcomeres
Leads to a increased compliance and allows for a greater EDV
Increase in venous return leads to a increase or decrease in EDV (preload)
Increase which leads to increase SV and increased ventricular stroke work
True or false:
From beat to beat, the heart can adjust its force of contraction to pump the volume of blood that fills it in the previous diastole
True
Heterometric regulations is based on the changes in
Volume
Afterload
The load against which the heart must contract to eject the blood
For the left ventricle, the major component of the afterload is the ________ and for the right ______
Left is the aortic pressure and the right is the pulmonary arterial pressure
Another component of afterload is the
Ventricular wall stress
Afterload increases with increasing pressure during systole and ______ with ventricular hypertrophy
Decreases
With increasing afterload the velocity
Decreases
Increasing aortic pressure represents _____ after load
Increasing
Will the increased afterload reduce SV?
Yep, systole occurs in a finite time
The heart must develop a higher pressure to open the aortic valve thus the shortening velocity will
Decrease
Afterload effects on cardiac performance are not a function of sarcomere length and are termed
Homeometric regulation
What might partically compensate for the reduction in SV due to increased afterload?
The venous return will be added to the increased ESV to give an increased preload (EDV)
An increase in afterload shifts the Frank-sterling curve _______ and to the _______ thus decreasing SV at any preload
Down and to the right
A decreased afterload shifts the F-S curve ___ and to the ____ thus increasing the SV at any preload
Upward and to the left
True or false:
Changes in preload alters Vmax
False, no changes
Increase in preload increases: (2)
- Velocity of shortening at a given afterload
2. Max w/out changing V,ax
Intrinsic measure of cardiac function independent of extrinsic factors like preload and afterload
Inortropy
Inotropic state is increased by
Sympathetic stimulation to the heart and by epinephrine by the adrenal medullary
Contractility is decreased by
Parasympathetic stimulation
Contractility is related to (2)
- To the rate of force development during ejection
2. Related to the ESPVR- end systolic pressure volume relationship
With increased inotropy there is an ______ force. (SV) at any preload
Increased
An increase in inotropy ______ velocity of shortening (SV) at any afterload
Increases
Contractility increases Vmax
Yep
Positive inotropic effects result from (3)
- Increased rate of delivery of Ca2+ to the myofibrils
- Increased binding of Ca2+ to troponin C
- Increased rate of cross-bridge cycling
Inotropic state can be influenced by other factors
Increased heart rate which can increase intracellular Ca2+
Loss of inotropy can lead to
Heart failure, cardiomyopathy and ischemia
What drugs can be used clinically to increase inotropy?
- digoxin
- B- agonist
Because preload affects cardiac function by changing the sarcomere length, this type of regulation is called
Heterometric regulation
The ejected volume will change to give the same ESV (2)
- Increased venous return, the extra blood over and above the normal EDV will be ejected
- If there is decreased venous return, the volume ejected will be decreased
