14- Cardiac Output & Contractility Flashcards by Staci Thomas

To understand Cardiac Output (CO), we need to consider…

Heart Rate (HR)
Contractility
Preload
Afterload

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Compared to Cardiac muscle contraction, Skeletal muscle contraction has more influence of _________ receptor inputs and relies more heavily on SR ________ levels and release.

Adrenergic

Calcium

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Cardiac _________ are used to treat heart failure.

Glycosides

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Briefly describe the mode of action for Cardiac Glycosides to treat heart failure.

1) Inhibition of Na+/K+ ATPase binding K+ binding site
2) Increases Na+ concentration
3) Decreases Ca2+ efflux through Ca2+/Na+ exchanger
4) Increase Ca2+ intracellular (more into SERCA)
5) Positive inotropic effect

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What is the formula for CO?

CO = HR x SV

***Stroke volume (SV) relates partially to myocardial contractility, but also to coupling factors

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Changes in CO related to length-tension relationship include a _________ inotropic or _________ inotropic effect. This modifies the speed or force of contraction, and is generally proportional to the amount of _________ that is available to Troponin on Actin filaments of the contractile apparatus.

Positive
Negative
Calcium

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This is the term for how much blood is ready to be pumped at the end of diastole before it contracts (Left Ventricular End-Diastolic Volume).

Preload

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Preload is the wall tension in the _______ ________ just before contraction is initiated. Think of this as fiber ________ at the end of diastole.

Left Ventricle
Length

***Can apply to Right Ventricle too!

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Preload is related to _______ _______ (i.e., more blood returning, greater preload).

Venous Return

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Volume at EDV also relates to venous return, so ________ _________ (or Q) = Venous Return (steady state).

Cardiac Output (CO)

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What is the Frank-Starling Relationship?

Volume of blood ejected by the ventricle depends on the volume present in the ventricle at the end of diastole.

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This term means the force opposing contraction, and is thought of as the pressure required to eject blood (open the Aortic Valve). For the Left Ventricle, it’s related to Aortic Pressure.

Afterload

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What is Afterload equal or greater than?

Aortic or Pulmonary Artery pressure

***Aortic for Left Ventricle and Pulmonary for Right Ventricle!

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Velocity of shortening (aka contraction) (INCREASES/DECREASES) as Afterload (INCREASES/DECREASES).

Decreases
Increases

***If Afterload is high and making the ventricle have a higher pressure and force to contract, then the velocity of the contraction will be slower.

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Where are Preload and Afterload both located on the Left Ventricular Pressure and Ventricular Volume graphs?

At the end of Isovolumetric Contraction

***Afterload = Aortic valve opens

***Preload = Aortic valve opens, causing sudden drop in volume

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This is the term for the volume of blood ejected by the ventricle with each beat.

Stroke Volume (SV)

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What is the equation for SV involving systole and diastole?

SV = EDV - ESV

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What is the average SV?

70 mL

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This is the term for the fraction of the EDV ejected in each SV. It is a measure of efficiency and contractility.

Ejection Fraction (EF%)

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What is the equation for the EF%?

EF% = SV / EDV

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What is the average EF%?

55%

***Reduced in heart failure

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This is the term for the total volume of blood ejected by ventricle per minute.

Cardiac Output (CO)

***Also called Q

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What is the average CO?

5 L/min

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What are the coupling factors involved with CO that relate to contractility?

Preload

Afterload

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If there is an increase in Preload, what happens?

Increases CO and contractility (in a healthy heart)

If there is an increase in Afterload, what happens?

Decreases CO ***To overcome, the heart must increase contractility OR increase HR

Increase HR (positive ________ effect) will increase contractility (positive ________ effect).

Chronotropic | Inotropic

Increased HR causing increased contractility is also called the Positive _________ Effect or ________ ________. This means more _________ is entering the cell and is taken up by the SR. It can potentially cause Post-extrasystolic potentiation (arrhythmia, extra beat).

Staircase Bowditch Staircase Calcium ***As HR increases, there is not enough time to clear the Calcium, which causes the leftover to go into the SR and cause the following beats to pump harder.

Sympathetics cause a (POSITIVE/NEGATIVE) inotropic effect on CO.

Positive ***Increases contractility

What receptors are used by the Sympathetics to activate the positive the inotropic effect on the heart?

Beta-Adrenergic ***NT is Norepinephrine

For Sympathetics, once the Beta-Adrenergic receptors are activated, there is ___________ of Sarcolemmal Ca2+ channels which allows it to enter the cell.

Phosphorylation

For Sympathetics, once the Ca2+ enters the cell it goes to the SR via SERCA. There is an inhibitory protein that will inhibit SERCA and affect the Ca2+ from being utilized correctly. However, when phosphorylated this protein is inhibited and this allows SERCA to do its job. This protein is...

Phospholamban

For Sympathetics, the phosphorylation of _________ is inhibitory and will lead to relaxation. Normally, Ca2+ will bind with Troponin C and create a complex to cause muscle contraction. This is what is being inhibited.

Troponin I

T/F. Parasympathetics have a negative inotropic effect in the ventricles only, it has no influence on atrial myocytes.

False. Parasympathetics have a negative inotropic effect in the atria only, it has no influence on ventricular myocytes.

What type of receptors are used for Parasympathetics for the heart?

Muscarinic ***NT is ACh

For Parasympathetics, the activation of the Muscarinic receptors will cause a decrease of inward ________ current during plateau and ACh will increase an outward ________ current via the _______ channel.

Ca2+ K+ K+/ACh

For the Ventricular Pressure-Volume Loop (slide 25, etc) what is the orange dotted line representing?

End-Systolic Pressure-Volume Relation (ESPVR)

For the Ventricular Pressure-Volume Loop (slide 25, etc) what does the #1 indicate?

Preload ***Marks end of diastole (pressure is low)

For the Ventricular Pressure-Volume Loop (slide 25, etc) what does the #2 indicate?

Afterload ***Aortic valve opens

For the Ventricular Pressure-Volume Loop (slide 25, etc) what is happening from #1 to #2?

Isovolumetric Contraction

For the Ventricular Pressure-Volume Loop (slide 25, etc) what is happening from #2 to #3?

Ventricular ejection (contraction) ***Pressure reaches a maximum between 2 and 3

For the Ventricular Pressure-Volume Loop (slide 25, etc) what is happening from #3 to #4?

Isovolumetric Relaxation * **Systole ends at 3 * **Tricuspid/Bicuspid Valves open at 4

For the Ventricular Pressure-Volume Loop (slide 25, etc) what is happening from #4 to #1?

Ventricular filling

What happens to the Ventricular Pressure-Volume Loop if there is increased Preload?

-- Means there is increased Left ventricular volume (so line from 4 to 1 is longer) -- Greater volume means more blood is going to be ejected out, so there is increased SV (width of pressure-volume loop is bigger) -- More blood is being pumped out, so there is greater venous return and an overall increased blood volume

What happens to the Ventricular Pressure-Volume Loop if there is increased Afterload?

-- Increased Afterload means the Aortic or Pulmonary A. pressure is higher (so line from 1 to 2 is longer) -- This makes it harder to eject blood (so line from 2 to 3 is higher) -- Due to the increased pressure and difficulty for blood to be ejected, there is a decreased amount of blood being pumped making the SV smaller (width of pressure-volume loop is smaller -- increased ESV, which is #4)

What happens to the Ventricular Pressure-Volume Loop if there is increased contractility?

-- Increased contractility means more blood is being pumped, so an increased SV (width of pressure-volume loop is bigger -- decreased ESV, which is #4) -- There is an increase in Aortic pressure as well, so the ventricle must eject blood against a higher pressure (so line from 2 to 3 is higher)

Volume Work = ________ _______

Cardiac Output

Pressure Work = ________ ________ (this is bad!)

Aortic Pressure

Minute Work = _______ _______ x ________ ________

``` Cardiac Output (CO) Aortic Pressure ``` ***Volume Work (CO) and Pressure Work (Aortic Pressure)

Stroke Work = _______ _______ x _______ _______

``` Stroke Volume (SV) Aortic Pressure ``` * **Stroke Work is performed by the Left Ventricle * **This is the area within the pressure-volume loop

When the heart is constantly working against pressure (i.e., hypertension), what will happen to the heart?

Hypertrophy ***Mainly the left ventricle will hypertrophy because it's the one having to pump the blood to the rest of the body

Pressure Work (Aortic Pressure) is costlier than Volume Work (CO). The largest percentage of ________ consumption is for Pressure Work (internal work or heat) rather than CO.

Oxygen

The (RIGHT/LEFT) Ventricle must proportionally work harder than the (RIGHT/LEFT) Ventricle despite CO being similar because systemic pressure is greater than pulmonary pressure.

Left | Right

What are conditions that increase Left Ventricular pressure work?

Aortic Stenosis | Systemic Hypertension

What is the Fick Principle for the measurement of CO?

CO = Oxygen Consumption / (Oxygen, pulmonary vein - Oxygen, pulmonary artery)

The Cardiac Function Curve will (INCREASE/DECREASE) if the venous return increases, and EDV and End-Diastolic fiber length will (INCREASE/DECREASE).

Increase | Increase

T/F. At steady state, the volume of blood as CO ejected by the Left Ventricle equals or matches the volume it receives in venous return.

True

At Equilibrium, CO = Venous Return and can only occur at a specific ________. This equilibrium point will vary depending on the state of the CV system.

Preload

What is a normal CO and P(RA)?

``` CO = 5 L/min P(RA) = +2 mmHg ```

What happens to the Cardiac Function Curve if there is increased inotropy (contractility), which leads to increased HR and decreased Afterload?

The curve is enhanced and the slope goes up.

What happens to the Cardiac Function Curve if there is decreased inotropy (contractility), which leads to decreased HR and increased Afterload?

The curve is depressed and the slope goes down.

Pmc = ______ or ______ mmHg (mean circulatory filling pressure or mean systemic pressure). When there is no CO and depends entirely on vascular compliance and blood volume.

+7 | +8

As the P(RA) starts to fall below zero, the increase in CO begins to plateau because the ______ ______ collapses, thus limiting venous return to the heart.

Vena Cava

If there is a Positive Inotropic effect, what happens to the CO curve and the Venous Return curve?

CO Curve will increase its slope (move higher). | Venous Return Curve does not move.

If there is a Negative Inotropic effect, what happens to the CO curve and the Venous Return curve?

CO Curve will decrease its slope (move lower). | Venous Return Curve does not move.

If there is an increased TPR, what happens to the CO curve and the Venous Return curve?

CO Curve will decrease its slope (move lower). | Venous Return Curve will decrease its slope (move lower).

If there is a decreased TPR, what happens to the CO curve and the Venous Return curve?

CO Curve will increase its slope (move higher). | Venous Return Curve will increase its slope (move higher).

If there is an increased Blood Volume, what happens to the CO curve and the Venous Return curve?

CO Curve will not move. Venous Return Curve does not change slope but it moves higher.

If there is a decreased Blood Volume, what happens to the CO curve and the Venous Return curve?

CO curve will not move. Venous Return Curve does not change slope but it moves lower.

In cardiac failure, what things would you expect to see on the CO and Venous Return graph?

Decreased Inotropy (CO curve and slope is lower) Decreased vascular compliance Increased blood volume (Venous Return curve is lower) Increased SVR/TPR (Both curves and their meeting point is lower)

14- Cardiac Output & Contractility Flashcards

(70 cards)