Contractility and Cardiac Output

Question 1

what physiological aspect of contractions does Cardiac Muscle rely on more than Skeletal muscle

Answer 1

Cardiac Muscle: More influence of adrenergic receptor inputs

and also relies more heavily on Sarcoplasmic Reticulum Calcium and its release

Question 2

What are the functions of Cardiac Glycosides and what are their modes of action

Answer 2

they inhibit the Na/K+ ATPase binding site for K+

this then prevents the release of Na+ and increases its concentration

this then decreases the Ca+ efflux out of the cell through the Ca+/Na+ exchanger

then increases the Ca+ intracellular

leads to a positive inotropic effect

Question 3

what is the equation for Cardiac output and its factors

Answer 3

CO= HR x SV

heart rate times stroke volume equals the cardiac output

Question 4

What is the Length tension relationship and Cardiac output

Answer 4

Changes in cardiac output related to length-tension relationship

a positive ionotropic effect leads to an increase in Cardiac output

a negative ionotropic effect leads to a decrease in cardiac output

Generally proportional to the amount of calcium that is available to troponin on actin filaments of contractile apparatus

Question 5

What is preload and what is it related too

Answer 5

Left Ventricle End Diastolic Volume (amount of blood ready to be pumped when diastole is over)

-wall tension in Left ventricle just before contraction
(fiber length at end of diastole from where it will contract)

it is related to the venous return (more venous return greater preload)

Question 6

Frank-Starling Relationship

Answer 6

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

therefore, more blood in ventricle means more stretch means more contraction

this relates length tension to functionality

Question 7

what is afterload

Answer 7

Force opposing contraction or as the pressure required to eject the blood (open the aortic valve)

-essentially equal to the aortic or pulmonary pressure

Question 8

Where is preload and afterload within the Cardiac cycle

Answer 8

Preload: Left ventricular End Diastolic volume
-end diastolic fiber length from where the muscle will begin its contraction

Afterload:
-for the left ventricle the aortic pressure (pressure needed to open the Aortic valve

Question 9

What is the stroke Volume, Ejection fraction, and Cardiac output numerically

Answer 9

Stroke volume: volume of blood ejected by ventricle with each beat
SV= EDV-ESV (usually about 70 mL)

Ejection Fraction: Fraction of the EDV ejected in each stroke volume

• measure of efficiency and contractility
• EF% = SV/EDV (usually about 55%)

Cardiac Output: total volume of blood ejected by ventricle per minute
-CO=SVxHR (usually about 5 L/min)

Question 10

if preload changes what happens to Cardiac Output

Answer 10

Preload increases = increase cardiac output and contractillity

Preload decreases = decrease in cardiac ouput and contractillity

Question 11

if afterload changes what happens to Cardiac Output

Answer 11

Afterload increases = decrease in cardiac output

therefore body must increase contractillity or increase HR to overcome the afterload

Question 12

How does Heart Rate effect Contractillity

Answer 12

Increased Heart Rate (positive chronotropic effect) increases contractillity (positive inotropic effect)

Positive staircase effect (bowditich staircase)

• more Ca+ enters cells and taken up into SR
• post-extrasystolic potention (arrythmia and extra beat)

Question 13

What is the physiological effect sympathetics have on Cardiac output and mechanism

Answer 13

Positive inotropic effect: B-AR activation

• Phosphorylate the sarcolemmal Ca channels (increase intracellular ca+
• Phosphorylate of phospholamban (pump more Ca from SR)
• Phosphorylate to inhibit Troponin I (an inhibitor of troponin C

Question 14

what is the physiological effect parasympathetics have on Cardiac output and its mechanism

Answer 14

Negative inotropic effect in Atria only!

• Muscarinic receptor activation
• decrease inward Ca+ current during pateau (phase 4 of SA)
• ACh increases outward K+ current via K+ ACh channel

Question 15

in an Ventricular Pressure- Ventricular Volume Loop what is happening from 1 to 2?

Answer 15

1 is the preload
2 is the afterload

1 to 2: Isovolumetric contraction

• end of diastole and pressure is low
• must increase pressure to past afterload to eject blood and decrease volume

Question 16

in an Ventricular Pressure- Ventricular Volume Loop what is happening from 2 to 3

Answer 16

2 to 3 is Ventricular ejection
pressure will reach a maximum point in middle

-if take starting volume and subtract to end volume will give you the stroke volume

aortic valve is open, AV valve closed

Question 17

in an Ventricular Pressure- Ventricular Volume Loop what is happening from 3 to 4

Answer 17

Isovolumetric relaxation

• point 3 is systole ends and ventricle begins to relax (all valves are closed)
• Ventricular pressure falls quickly but volume remains the same
• pressure must fall below atria to allow for bicuspid valve to open (point 4)

Question 18

in an Ventricular Pressure- Ventricular Volume Loop what is happening from 4 to 1

Answer 18

Ventricular filling

Aorta valve close, AV valve open

Question 19

what is a dotted line on a Ventricular Pressure vs Volume loop

Answer 19

End-systolic pressure volume relation (ESPVR)

has to do with contractillity

Question 20

what happens to Pressure volume loop of the ventricle as there is an increase of Preload

Answer 20

More venous return, and more blood volume, meaning greater EDV

Therefore, afterload stays the same and contractillity but there is an increase in stroke volume

Question 21

what happens to Pressure volume loop of the ventricle as there is an increase in afterload

Answer 21

the increase afterload can be aortic stenosis, or hypertension

greater pressure needed to compensate

therefore a reduce in stroke volume and a reduced Ejection fraction %

Question 22

what happens to Pressure volume loop of the ventricle as there is an increase in cpontractillity

Answer 22

may be caused by a adrenergic stimulation

increased stroke volume and increased Ejection fraction percentage

less blood left in the heart

Question 23

what is Volume work, pressure work, minute work, stroke work

Answer 23

Volume work: cardiac output

Pressure work: aortic pressure

Minute work: Cardiac output x aortic pressure (volume work x pressure work)

Stroke work: (performed by the left ventricle) = stroke volume x aortic pressuure
-area within the pressure volume loop

Question 24

where does the largest percentage of oxygen consumption go in the heart

Answer 24

goes to pressure work rather than volume work

this is because the left ventricle has to work harder than the right ventricle due to the fact the systemic pressure is greater than the pulmonary pressure

Question 25

The fick Principle

Answer 25

Measurement of cardiac output

Cardiac output = O2 consumption/([O2] pulmonary vein- [O2]pulmonary artery)

Question 26

what is the relationship between the CO and Venous return in the cardiac function and vascular function curve

Answer 26

x axis: Right atrial pressure
y axis: Cardiac output and venous return

Cardiac function curve: venous return increases and right atrial pressure increases
also end diastolic volume and end diastolic fiber length increases

Vascular function curve: gives the cardiac output in regards to the pressure of the right atrium
the mean systematic pressure will always be +7 or +8 when there is no cardiac output due to the vascular compliance and blood volume

Question 27

what does it mean at the equilibrium of the Cardiac output and Venous return vs Right atrial pressure graph

Answer 27

at equilibrium the Cardiac output= the venous return and can only occur at specific preload

normal: CO 5L/min and PRA = +2mmhg

this is the point where the cardiac function and vascular function graph intersect

Question 28

How is the cardiac function enhanced and depressed

Answer 28

enhanced:
increase in inotropy
increase in Heart rate
decrease in afterload

depressed:
decreasde in inotrophy
decrease in heart rate
increase in afterload

Question 29

How does changes in Total peripheral resistance effect the CO and Venous return graph

Answer 29

increased TPR: decrease the equillibrium of cardiac output but not change the right atrial pressure

decreased TPR: will increase the equillibrium of cardiac output but not affect the right atrial pressure

Question 30

how does changes in blood volume affect the CO and venous return graph

Answer 30

increase in Venous return graph in L/min and a increase in right atrial pressure

Question 31

what occurs in the CO and venous return graph when there is cardiac failure

Answer 31

Decrease in intotropy
Decrease in vascular compliance
increase in blood volume
increase in SVR/TPR