Intro to Cardiac Physiology

Question 1

the myocardium has 2 jobs:
to contract. This phase is called ____.

to relax. This phase is called ___.

Answer 1

the myocardium has 2 jobs:
to contract. This phase is called systole.

to relax. This phase is called diastole.

Question 2

electrical stimulation:

1. ____ node generates electerical impulse
2. Impulse is conducted to ___, ___node, and ventricles
3. Impulse enters cell membranes and induces changes to ion channels

Answer 2

Sino-atrial node generates electerical impulse
Impulse is conducted to atria, AV node, and ventricles
Impulse enters cell membranes and induces changes to ion channels

Question 3

outlinethe biochemical events that occur so that cardiac muscle can contract

Answer 3

• voltage gated ion channels change shape with a change in voltage or arrival of action potential
• Ca++ channels open with depolarization
• Ca++ enters cell and stimulates ryanodine receptors on the sarcoplasmic reticulum (SR)
• the SR also releases stored up Ca++ cytoplasmic
• Ca++ in greatly increased
  Afterwards, troponin binds Ca2+ and moves the tropomyosin that covers up the active sites on the actin. It allows myosin head to bind onto activ filament and undergo contraction.

Question 4

outline the different types of troponins

Answer 4

Question 5

Actin and Myosin Mechanics

1. Ca++ binds troponin, which moves tropomyosin, and exposes the binding site on action.
2. myosin head, bound to ATP, binds actin
3. ATP is hydrolyzed, power stroke occurs
4. ADP and Pi are released
5. myosin __ ___ ___ and releases from actin and resets myosin to starting position

Answer 5

1. Ca++ binds troponin, which moves tropomyosin, and exposes the binding site on action.
2. myosin head, bound to ATP, binds actin
3. ATP is hydrolyzed, power stroke occurs
4. ADP and Pi are released
5. myosin binds new ATP and releases from actin and resets myosin to starting position

Question 6

how is troponin a marker for MI?

Answer 6

When cardiac cells die, they break open. Troponin levels in the blood increase when there is cardiac cell death

Question 7

How does Ca2+ affect cardiac relaxation?

Answer 7

it is pumped back into the sarcoplasmic reticulum via SERCA (sarco/endoplasmic reticulum calcium ATPase)
SERCA is regulated by phospholamban (PLB)

Question 8

Valves open and close according to ___ __

Answer 8

Valves open and close according to pressure differences

Question 9

When will valve 1 open?

Answer 9

when A>B. the pressure will force fluid into B chamber.

Question 10

when does isovolumetric contraction occur?

Answer 10

• when there is no change in volume between chambers. occurs when both the in and out valves are closed. can occur with contraction and can occur with relaxation.

it would occur when B>A and C>B

Question 11

is the mitral valve bi or tri cuspid

Answer 11

Mitral valve – located between the left atrium and the left ventricle (left atrioventricular orifice). It is also known as the bicuspid valve

Question 12

Remember – in diastole:
mitral valve is __
aortic valve is __

when does systole start?

Answer 12

Remember – in diastole:
mitral valve is open
aortic valve is closed. The ventricle is filling.

systole starts when the mitral valave closes. Both valves are now closed. This occurs in early ventricular contraction (raising pressure)–this is isovolumetric contarction, until the aortic valve opens.

Ejection phase occurs when the aortic valve is open.

systole ends when the aortic valve closes. Both valves are now closed. Soon the mitral valve will open again for the next cycle of ventricular filling.

Question 13

note:

Question 14

preload and when does it occur

Answer 14

ventricular filling up the haert prior to contraction. (VENOUS RETURN) this stretches the muscle because of the more fluid. occurs in diastole.

Question 15

afterload and when does it occur

Answer 15

Preload is the initial stretching of the cardiac myocytes (muscle cells) prior to contraction. It is related to ventricular filling. Afterload is the force or load against which the heart has to contract to eject the blood. … Afterload is the ‘load’ to which the heart must pump against. It opposed contraction

Question 16

preload is the volume of blood inside the ventricle right before the ventricle contract.s this is often called the ___ ___ volume

Answer 16

end diastolic volume. (LVEDV)

Question 18

explain how “myocardium as a spring” is related to the frank-starling curve

Answer 18

• the heart is somewhat of a spring if it is filled to optimum volume, this puts a little stretch to the myocardium
• when the heart then contracts, there is extra contraction that occurs
  this relationship between force of contraction and preload is described by the Frank-Starling curve

Question 19

JVP estimates the filling pressure of the ___ ___

Answer 19

estimates the filling pressure directly of the right atrium (pulmonary tract side of the heart)

*a CVP also measures right atrium. Tells us the pressure directly of the right atrium. We would do this in patients with hemodynamic instability (CAD, trauma),

Question 20

note on preload:

Question 21

2 definitions of afterload

Answer 21

1. resistance to ventricular ejection; it’s the pressure that the heart must overcome in order to contract and send blood to aorta
2. wall tension of the ventricle.

Question 22

____ pressure = increased afterload

Answer 22

increased pressure = increased afterload.

• if there’s lots of resistnace/pressure in the ventricle, then the ventricle must contract hard enough to offset the resistance. there is a lot of pressure that is resisting contraction. this would cause high blood pressure.

Question 24

examples of high afterload.

Answer 24

1. aortic valve does not fully open/it’s sticky (aortic stenosis), making it dificult to eject blood.
2. high pressure in the aorta (hypertension)– normally, blood flows from higher pressure ventricle to lower pressure aorta through pressure gradients. but if there is hypertension and the aorta already has high pressure, the ventricle must generate very high pressure to eject blood. this high blood pressure might be due to blockage/plaquee.

Question 25

note: overall, afterload is not good - it requires the heart to generate excessive work - difficult to eject blood to the aorta, resulting in a smaller stroke volume. - results in changes in cardiac muscle (remodeling) - can burn out the heart and cause heart failure

Question 26

T/f contractility is independent of ventricular filling

Answer 26

true. the heart can contract better when it is optimally filled, but filling the heart does not increase contractility. - if you limit blood supply, contractility decreases. Contractility is independent of preload. - however, giving someon ean injection of adrenaline would increase force of contraction = high contractility. - myocardial ischemia can reduce contractility.

Question 27

how does Ca2+ channel blocker affect contractiltity?

Answer 27

if CA2+ is blocked, it decreases intracellular Ca2+, resulting in decreased actin and myosin interaction, resulting in decreased contractilty

Question 28

stroke volume equation

Answer 28

diastolic volume - systolic volume.

Question 29

3 determinants of stroke vol

Answer 29

1. preload (higher usually produces larger SV) 2. contractility (higher produces large SV) 3. afterload (higher produces LOWER SV)-- because higher afterload means that it's hardwork for the heart to eject blood.

Question 30

cardiac output equaiton

Answer 30

CO= SV x HR therefore CO = (EDV-ESV) x HR - this is he volume of blood pumped by the heart into the aorta in one minute.

Question 31

if your heart is weak and the stroke volume is low, it is possible that circulation will be inadequate unless the ___ \_\_\_ is very high

Answer 31

if your heart is weak and the stroke volume is low, it is possible that circulation will be inadequate unless the **heart rate** is very high

Question 32

BP equation

Answer 32

blood pressure = CO x SVR CO- more filling = higher pressure SVR = more squeeze = more resistance = higher pressure.

Question 33

explain the proportionality of blood pressure to cardiac output and blood vessel resistance

Answer 33

BP = COxSVR = directly proportional. - the more fluid you put into the arteries, the higher the pressure will be. - thus, BP is proportional to cardiac output - the more the arteries squeeze (constrict), the smaller the radius, the higher the resistance and the higher the pressure - thus, BP is proportional to resistance

Question 34

outline the relationship between vessel resistance and radius

Answer 34

as radius becomes smaller (vasoconstriction), resistance to flow is increased

Question 35

note: **vasodilation with hypotension** is always pathological _Systemic Vascular Resistance_ vasodilation = bigger diameter bigger diameter = lower resistance (SVR) lower resistance = more blood flow blood is warm and red, therefore: extremities will be warm and pink

Question 37

how can you measure SVR?

Answer 37

PA catheter on PE: high SVR: cool, pale, weak pulses low SVR: warm, pink, bounding pulses. lots of blood going to extremities because of vasodilation

Question 38

flow is proportional to ____ but inversely proportional to \_\_\_

Answer 38

flow is proportional to PRESSURE but inversely proportional to RESISTANCE

Question 39

Mean Arterial Pressure is the average, or area under the curve between \_\_\_and ___ pressures. The MAP is estimated to be about \_\_\_\_\_(fraction) the value from the diastolic to the systolic.

Answer 39

as you know there is systolic and diastolic pressure the “mean” or average or area under the curve is what is referred to as the MAP. - The MAP is estimated to be about 1/3 (fraction) the value from the diastolic to the systolic.

Question 40

a patients blood pressure is 89/56, calculate the MAP

Answer 40

MAP = DBP + (1/3(sys-dia)) = 56+ (0.33(89-56)) = 67

Question 41

what is an ejection fraction

Answer 41

**Describes how much (%) of the blood that is inside the ventricle gets ejected with one contraction.** Typical values are: 55-65% is normal 15-30% is very reduced (heart failure) \<10% is incompatible with life

Question 42

equation of ejection fraction

Answer 42

EF = stroke volume/ diastolic volume EF = (EDV-ESV)/ (diastolic vol)