Unit 4 - The heart as a pump Flashcards
What is this diagram representative of?
The cardiac cycle
What interval is the atrial kick phase?
P-Q
What happens during the atrial kick phase?
S4 ‘atrial gallop’ sound, increase in left ventricular volume, increase in left atrial and left ventricular pressure, AP slowly decreasing
What is happing to the atrium during the atrial kick phase?
It is depolarizing and then begins contraction
Why is the atrial kick phase important?
because it gives the ventricle the final volume it needs before it contracts
Is the atrial kick phase during diastole or systole?
It is the end of diastole and the beginning of systole
What is occuring during the R peak of the QRS complex?
it is the beginning of the S1 sound, left ventricular volume is at peak, left arterial pressure is at peak, it is the moment right before the pressure in the left ventricle increases, and action potential is decreasing
What is the R-S interval also known as?
isovolumic contraction
What is happening across the heart during isovolumic contraction?
S1 sound, left ventroicular volume is steady, left atrial pressure decreases, left ventricular pressure increases dramatically, action potential is at the lowest
Why does left ventricular volume remain steady during isovolumic contraction?
Because the aortic valve is closed
What events are occuring to the left ventricle during isovolumic contraction?
the ventricle is depolarizing and then begins to contract
Is isovolumic contraction considered a systolic phase or diastolic?
systolic
What is the S-T interval also known as?
the ejection phase
What is happening during the ejection phase?
Left ventricular volume decreases, Left arterial pressure increases slightly, left ventricular pressure reaches its peak and slowly declines, action potential hits peak and then begins to decline
Physiologically, what is the ejection phase also known as?
physiological diastole
Why does left ventricular volume decrease during the ejection phase?
because the semilunar valves open and the stroke volume enters the arteries
What event happens at the end of the t-wave?
isovolumic relaxation
What happens during isovolumic relaxation?
S2 ‘dub’ sound, Left ventricular volume remains steady, Left atrial and left ventricular pressure increases to peak, action potential is back to repolarized state
What phase happens after the t-wave, but before the T-P interval?
rapid filling
What happens during the rapid filling phase?
S3 sound, left ventricular volume increases, left atrial and ventricular volume is low, action potential is decreasing
Why does left ventricular volume increase during the rapid filling phase?
The atrioventricular valves have opened allowing blood to rapidly fill into the ventricle
What phase happens during the T-P interval?
diastasis
What is happening during diastasis?
left ventricular volume is steady, left atrial pressure and left ventricular pressure remain steady and equal, action potential is decreasing
What is cardiac output?
the volume of blood being pumped by the heart per unit time
How do you calculate cardiac output?
CO=SV x HR
How does increased heart rate affect cardiac output?
it increases it
How does increased contractility affect cardiac output?
it increases stroke volume which increases cardiac output
How does increased preload affect cardiac output?
it increases stroke volume, which increases ventricular filling which increases cardiac output
How does increased afterload affect cardiac output?
it increases left ventricular pressure so the ventricle is not able to eject as much blood which decreases stroke volume therefore decreases cardiac output
What are some methods for estimating contractility?
Ejection fraction, fractional shortening, dp/dt max
What is the ejection fraction?
relates SV to SVE is an index of the extent of LV fiber shortening
What is fractional shortening?
% change from diastolic to systolic left ventricle diameter
How is fractional shortening obtained?
by echocardiography
What is this?
A normal pressure volume loop for left ventricular pressure
What is happening in phase 1 of this diagram?
the left ventricle is filling
What is happening in phase 2 of this diagram?
the mitral valve closes, pressure rises in the left ventricle
What is happening between phase 2 and phase 3?
isovolumic contraction
What is happening in phase 3 of this diagram?
The aortic valve opens,
What is happening in phase 4 of this diagram?
Peak pressure of the ventricle is reached
What is happening between phase 4 and 5 of this diagram?
ejection from the ventricles
What happens in phase 5 of this diagram?
the aortic valve closes, the end of the ejection phase, the beginning of ventricular relaxation
What is happening between phase 5 and phase 6 of this diagram?
isovolumiv relaxation
What happens at phase 6 of this diagram?
the mitral valve opens and the ventricle begins filling
How does increased contractility affect the normal pressure loop?
the end systilic pressure shifts to a lower ventricular volume (to the left), peak pressure increases
How does increased preload affect the normal pressure loop?
The ventricular phase is longer due to increased preload, contraction is the same, but peak pressure is higher
How does increasing afterload affect the pressure volume loop?
ventricular pressure is higher, the period between phase 2 and 3 extends, the peak increases, the ejection phase is shorter because it will not get back to end systolic volume
How is the law of LaPlace calculated?
Wall stress = (P x radius)/wall thickness
The bigger the left ventricle, the ______ the all stress.
greater
The greater the systolic pressure, the _______ the wall stress.
greater
How does an increase in wall stress relate to O2 intake?
it increases
What is eccentric hypertrophy?
chronic increase in volume load
How does volume overload lead to eccentric hypertrophy?
volume overload leads to increased diastolic wall stress which leads to increased sarcomere in series
What is concentric hypertrophy?
chronic increases in systolic pressure
How does pressure overload lead to chronic hypertrophy?
pressure overload leads to increased systolic wall stress, which leads to increased sarcomeres in parallel which leads to CH
What are the five determinants of ventricular filling?
Active relaxation of the myocardium, Ventricular compliance, Venous return, Duration of diastole, Atrial contraction
How does active relaxation affect normal vetricular filling?
When the AV valves open, the ventricle is still actively relaxing causing it to aspirate some blood from the atrium
How does reduced ventricular compliance affect diastolic function?
there is higher filling pressure which leads to smaller end diastolic volume
What does ventricular compliance depend on?
Ventricular dimensions, Wall thickness, Muscle activity (active relaxation), Wall composition, External compression
What is dp/dt max?
the slope of isovolumic contraction
What does a steep slope of dp/dt max indicate?
higher contraction
Where is the sympathetic innervation of the heart?
the entire heart
What are the effects of sympathetic stimulation?
increase contractility, increases rate of relaxation by reducing rate of affinity for Ca for troponin and by accelerating uptake of Ca into SR by phosphorylating PL, increase heart rate, increase AV conduction
Where does the parasympathetic system innervate?
SA and AV nodes
What is the affect of parasympathetic innervation?
Heart rate decreases, AV conduction decreases, Contractility decreases
