Contractility And Cardiac Output Flashcards by Ann yo

What are the differences b/w skeletal and cardiac muscle?

In cardiac:

More influence of adrenergic receptor input
&
Relies more heavily on SR Ca levels and release

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What are cardiac glycosides used to treat?

Mechanism of Action?

Tx heart failure

inhibits Na/K ATPase binding K binding site
increases Na concentration
decreases Ca efflux thru Ca/Na exchanger
increases Ca intracellular

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What is the formula to calculate

Cardiac Output?

CO = HR x SV

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What is stroke volume?

Relates partially to myocardial contractility but also to coupling factors (preload & afterload)

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How do you exact changes in CO?

Related to length tension relationship

-generally proportional to amount of Ca that is available to Troponin on actin filaments of contractile apparatus

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What is Preload?

Amount of blood ready to be pumped, diastole

Left Ventricle- End Diastolic VOlume

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What is LV EDV?

Wall tension in LV just before contraction is initiated

Aka fiber length at end of diastole

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What does more blood returning to the RV mean?

Greater preload

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What will volume at EDV be related to>?

Related to venous return

CO(Q) = Venous REturn (Steady State)

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What is the Frank Starling Relationship?

More blood that comes back to LV, the more that is going to get pumped

—> greater EDV = i am going to get pumped harder

(Volume of ejected blood depends on volume present in ventricle at end of diastole)

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What is afterload?

Pressure required to eject blood (open aortic valve)

Essentially equal to aortic/pulmonary artery pressure

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How is velocity of shortening affected by afterload?

Decreases as afterload increases

Greatest if afterload = 0

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When is preload measured?

At end of isovolumetric contraction period

Remember = end diastolic fiber length

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How does preload affect contractility?

Increase Preload

—> increases CO and contractility

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How does afterload affect contractilikty?

Increase afterload

—> decreases CO
—> increased HR

-heart must increase contractility to overcome decreased CO

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How do you calculate Stroke volume?

Normal value?

SV = EDV - ESV

~70 mL

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What is the normal value for ESV?

~50 mL

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What is stroke volume?

Volume of blood ejected by ventricle w/ each beat

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How do you calculate Ejection fraction?

Normal value?

EF% = SV / EDV

55%

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What is ejection fraction (EF%)?

Fraction of the EDV ejected in each stroke volume

-measure of efficiency and contractility

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What is cardiac output?

Total volume of blood ejected by ventricle per minute

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What is the normal value of CO?

5 L per minute

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How does HR affect contractility?

Increased HR —> increases contractility (SV)

What is the Positive Staircase Effect (bowditch staircase)?

Auto regulation method by which myocardial tension increases w/ an increase in heart rate

-more stimuli sent to muscle
—> contractions show successive increase in amplitude

What is the positive staircase effect caused by?

More Ca enters cells and is taken up into SR

What is the sympathetic influence on CO?

Positive inotropic (SV) effect -Beta AR activation 1. Phosphorylates sarcolemma Ca channels 2. Phosphorylates phospholamban (stimul.) 3. Phosphorylates Troponin I (inhib.)

What is the parasympathetic influence on CO?

Negative inotropic effect IN ATRIA ONLY - affecting PHASE 4 (RMP) (No influence on ventricular myocytes) Muscarinic receptor activation 1. Decreases inward ca current during plateau 2. ACh increases outward k current

in a ventricular pressure-volume loop, What does the right handed vertical line from point 1 —> point 2 represent?

Isovolumetric contraction

What is point 1 on a Ventricular Pressure-Volume Loop?

End of diastole = EDV = preload - so pressure is low - but volume would be high

What is Point 2 on a Ventricular Pressure-Volume loop?

Point where ejection of blood begins = when aortic valve opens = Afterload So pressure is high (around ~70-80) And volume is same as preload

What is Point 3 in a Ventricular Pressure VOlume Loop?

End of systole - closing of Aortic valve ESV too

What does the line between points 2-3 represent?

Ventricular ejection -pressure will reach a max. B/w these two points

How do you calculate SV using the Ventricular Pressure Volume loop?

SV = EDV - ESV (volume) SV = Point 1/2 - point 3/4

What is point 4 in a Ventricular PRessure-VOlume Loop?

Represents the opening of the Mitral/tricuspid valve

What does the line b/w Points 3 and 4 represent?

Isovolumetric relaxation -ventricular pressure falls quickly but volume (ESV) remains constant

What does the line b/w Points 4 and 1 represent?

Ventricular filling

How will the Ventricular Pressure-volume loop change w/ increased preload?

-more venous return, more blood volume Points 1 and 2 move laterally =greater EDV = GREATER Stroke volume -afterload and contractility remain constant

How will the Ventricular Pressure-volume loop change w/ increased Afterload?

Point 2 moves up, points 3 and 4 move closer (graph becomes taller) - greater pressure needed to open aortic valve - reduced Stroke volume - reduced ejection fraction

How will the Ventricular Pressure-volume loop change w/ increased contractility?

-points 3 and 4 will move laterally, point 2 up just a bit - increased SV - increased EF% - less blood left in heart

What can cause increased afterload?

Due to aortic stenosis or hypertension

What can cause Increased Contractility

Adrenergic stimulation

What is volume work?

Cardiac ouput

What is pressure work?

Aortic pressure

What is Minute work re: Cardiac work?

CO x Aortic pressure Or Volume work X Pressure work

What is Stroke work?

SV x Aortic pressure = area w/in the pressure volume loop

What performs stroke work?

Left ventricle

Is pressure work or volume work more costly?

Pressure work uses the largest percent of O2 consumption

Why does the LV work proportionally harder than the RV despite similar COs?

Bc systemic pressure is greater than pulmonary pressure and can be further accentuated by conditions that increase LV pressure work I.e. aortic stenosis or systemic hypertension

What is the fick principle?

Measure of CO O2 consumption / [(o2-pulm. V.) - (o2-pulm. A.)]

What is the relationship b/w CO adn Venous return?

At steady state, the volume of blood as cardiac output ejected by the LV equals the volume it receives in venous return CO = Venous return

What are the parameters needed for CO to equal VR?

At equilibrium CO = VR RA pressure = ~+2 mmHg CO/VR = 5 L/min.

What does the vascular function curve tell us?

Can figure out the Mean Systemic Pressure (MSP) by where it crosses x-axis (Bc there is no CO there and it completely depends on vascular compliance and blood volume)

How does Cardiac failure affect cardiac and vascular function?

Decreased CO and SV -veins are normal- just heart is failing -increased blood volume But systemic vascular function changes to help restore CO —> Decreased vascular compliance —> Increased SVR/TRP

How does exercise affect cardiac function?

Decreased TPR —> increased CO —> increased VR

How does hemorrhage affect cardiac function?

Increased TPR —> decreased CO —> decreased VR

How does increased Blood volume affect cardiac function?

Increased BV = more for veins to return but heart still pumps out same amt. = no change in CO =increased VR