Cardiac Cycle Flashcards
Systole
Contraction
Blood is ejecting
Diastole
Relaxation
Filling
How much does systole do and in what time?
ejects 2/3 of blood
total time = 1/3
How much does diastole do and in what time?
Coronary blood flow filling
total time = 2/3
As you increase heart rate, what is compromised?
Filling - diastole
Movement of blood depends on
Pressure Gradient
What generates the pressure
The heart - by contracting
Purpose of isovolumetric contraction
btw r and s - beginning of systole
causes increase in ventricular pressure
we need to exceed aortic pressure so blood can go from LV to body
End Systolic Volume
What is left in the heart after contracting
End Diastolic Volume
What we filled the heart/ventricle with
EDV - ESV
120-50 = 70
70mL is now in the aorta - this is stroke volume - how much we ejected from the heart
Isovolumetric relaxation purpose
drop pressure
we want to refill heart again so need gradient
need to lower ventricular pressure so its lower than atrial
As filling heart, which will be higher ventricular or atrial
atrial will always be higher during filling
When ventricular is higher than atrial, where will flow go? if valve open
back into atrium
Need to close valve so close AV valves
S1
Closure of mitral and tricuspid valves
lub
S2
closure of aortic and pulmonary valves
dub
S3
rapid ventricular filling
not typically audible in adults
Might indicate congestive heart in adults
S4
active ventricular filling
not typically audible in adults
Stroke volume
How much work the heart is doing
About 70mL
Cardiac Output
Flow out of the heart
HR * SV
Ejection Fraction
SV/EDV
of what you filled the heart with, how much are you actually ejected
Normally about 55%, 30% in heart failure
EF is an index for what
How hard the heart is working
or its contractility
Heart Rate - how regulated
Para and Sym
Can also be intrinsic on its own 100 bpm
Heart rate impacts CO - inc heart rate, compensating so can inc CO
Stroke Volume - how regulated
Sympathetic Nerves
Contractile Strength
EDV - fill heart more
Regulation of Heart Rate - nerves
None needed!
Regulation of Heart Rate with nerves - Symp
F/F - Increases HR via cardiac accelerator nerves (innervate SA node) and then NE binds to B1 adrenergic receptors and inc HR
Regulation of HR with nerves - Para
Dec HR via vagus nerve, Ach binds to muscarinic cholinergic receptors in SA node
Inspiration does what to HR
Increases HR
Exhalation does what to HR
Decreases HR
Atropine
Muscarinic Antagonist - Parasympathetic tone
Propanolol
Beta Blocker - Sympathetic
Preventing inc in HR
At rest, we rely more on sym or para
more on sympathetic then parasympathetic
End Diastolic Volume - Regulation of SV
Preload
Length tension relation and amount of filling
Changing the length by how much you are filling it with
Aortic Pressure/Mean Arterial Pressure - Regulation of SV
Afterload
Pressure the heart pumps against to eject blood
Aortic pressure that heart is fighting against to get flow out
Inc in afterload will… (SV)
SV will decrease
Inc in preload will… (SV)
SV will increase
Strength of Ventricular contraction - Regulation of SV
Contractility
How forcefully the heart contracts
What is the major factor controlling Q
The amount of blood returning to the heart
The heart can do no more than pump out what it receives
Inc contractility does what to SV
Increase SV
Frank Starling Mechanism
EDV - Preload
Greater preload results in stretch of ventricles
Inc in stretch optimizes # of CB formation
And this leads to more force and more CO and more SV
As you stretch the heart you will…
Fill it and optimize CB formation
Ca affinity for TnC is greater with
sarcomere length
The skeletal muscle pump
Milking action of muscle
Rhythmic muscle contractions force blood toward the heart
Decreased venous pressure sucking more blood through muscle
Generally what does skeletal muscle pump do
Increase venous return back to the heart
Increase blood flow to muscle
What prevents backflow of blood
One way valves
EVD is also affected by
Venoconstriction
Respiratory pump - breathe in you are dec pressure and this facilitates bringing flow into the heart
Mean Arterial Pressure
Afterload
Force opposing the ejection of blood from ventricles
Increasing the afterload increases the force required by the heart to eject blood into aorta
You are dec pressure gradient - making heart work harder
Ventricular Contractility
Intrinsic ability of cardiac muscle to generate force at given fiber length
Independet of pre and after load
Usually associated with change in intracellular Ca
Ventricular Contractility is induced by
Circulating EPI and NE
Direct sympathetic stimulation of heart
B1 effects on tissues
Inc heart rate and glycogenolysis and lipolysis and contractility
B2 effects on tissues
Inc bronchodilation and vasoconstriction
A1 effects on tissue
Inc vasoconstriction
A2 effects on tissue
Opposes B1 and B2 receptors
CO =
HR x SV
HR - intrinsic and syp and para
SV - preload (EDV), afterload (MAP), contractility
SV =
EDV - ESV
Ways to evaluate contractility
Ejection Fraction
End Systolic Pressure Volume Relation
Change in pressure over change in time
Ejection Fraction
SV/EDV
Used as index for evaluating heart failure
less than 30%
End Systolic Pressure Volume Relation
Slope of a line connecting aortic valve closing to max isovolumetric pressure (max pressure achieved during systole)
Change in Pressure over Change in Time
Contractility alters rate of pressure developed
Increased Contractility does what to SV
Increases it
ESV Decreased
Increased Preload (filling) does what with SV
Increases it
EDV increased
Increased afterload (aortic pressure) does what to SV
Decreases it
ESV increased
Greater SV = what for the heart
greater work for the heart, makes it more efficient - is a good thing
What does efficiency of the heart mean
Work over expenditure
Expenditure = energy cost, or what you have to invest in it
Wall tension and energy expenditure
Wall tension is where most of the energy from the heart is going - this puts more stress (bad) on the heart
What are smaller fractions that are associated with energy expenditure
Kinetic energy and external work
Stress on heart is determined by what
- Afterload (greater wall tension required)
- HR (more time in systole)
- Rate Pressure Product
Rate Pressure Product
SBP x HR
How much investment you are making; the stress load (decreases with exercise)
Ideal stress on heart
Low wall tension and less time in systole
Heart Rate is affected by
Symp and Para NS (ANS)
Contractility is affected by
Symp NS
MI - dec contractility
Heart Failure - dec contractility
Preload is affected by
Venous return and EDV Blood volume Postural change Skeletal muscle contraction Respiration
Afterload is affected by
Hypertension
Arterial stiffness
Inc in TPR
At a given velocity of shortening, muscle exerts….
more tension if we stretch it with more preload
At a given afterload, shortening ____ if we stretch the muscle with more preload
Increases
Input into RA =
Output from LV
As you dec Rigth Atrial Pressure you will do what to venous return (flow)
Increase it
Y intercept of Vascular Function Curve
RAP of zero - no more venous return
X intercept of Vascular FUnction Curve
Pressure when CO is 0
Mean circulatory pressure
Slope of Vascular Function Curve depends on
Venous Compliance
If you dec RAP…
you inc gradient for filling inc venous return increase preload Inc SV inc CO
