ICL 1.5: Principles of Cardiac Physiology I: The Cardiac Cycle & Normal Heart Sounds

Question 1

what is the normal heart rate for adults?

Answer 1

60-100

Question 2

what is a hypertensive crisis?

Answer 2

180/120 and above

elevated BP is 120-129

HTN stage 1 is 130-139

HTN stage 2 140+

Question 3

what are the normal intracardiac pressures in the atria?

Answer 3

RA = 2-8 but usually around 4

LA = 2-10 but usually around 8

LA pressure is almost always higher than the RA pressure to protect against right-left shunting and possible stroke

Question 4

what are the normal intracardiac pressures in the ventricles?

Answer 4

RV = 15-30 systole/2-8 diastole

LV = 100-140 systole/3-12 diastole

so if the RA pressure is 4 then the RV pressure MUST be lower than it because blood goes from high to low pressure

Question 5

what are the normal intracardiac pressures in the pulmonary artery?

Answer 5

15-30 systolic

4-12 diastolic

it needs to be around 10 diastolic so that it’s higher than the right ventricle diastolic pressure

Question 6

what is wedge pressure?

Answer 6

the pressure in the left atrium

Question 7

why is it so important that the left atrium has higher pressure than the right?

Answer 7

clots!

you constantly throw clots to your lungs and your lungs usually have no problem handling that – what doesn’t handle it fine is your brain!!

so it’s really important that all the clots coming from the IVC have to go to the RV and out the pulmonary artery – if they shunt to the left atrium from the right atrium like if you have a PFO then you are at a huge risk of a paradoxical stroke so it’s important that the LA pressure is higher to keep that blood from the right side from entering

so right to left shunting or higher pressure on the right side puts you at risk for having a stroke

Question 8

what is compliance?

Answer 8

LV has higher pressure than RV because what determines atrial pressure is compliance

compliance is the ability for the ventricle to relax; how well can it relax to accommodate blood?

the LV is a thicker ventricle so it doesn’t relax as well and isn’t as compliant

Question 9

what determines systolic blood pressure?

Answer 9

the systolic BP in the left ventricle!!

Question 10

what determines the diastolic blood pressure?

Answer 10

the elasticity of the arteries, specifically the aorta

you stretch it out during systole and it wants to go back to its normal shape during diastole so the pressure of the artery trying to go back to its normal shape is the diastolic pressure

Question 11

what’s the oxygen saturation of the blood in the IVC and SVC?

Answer 11

75%

so 25% of your oxygen is extracted if you have normal cardiac output

if you have 60% saturation in the SVC that tells you that the cardiac output is low because the blood is going slower through the body and there’s been more time to extract more oxygen (provided your lungs are working well and there’s no shunts)

so there should only be a 25% discrepancy between the left and right side in oxygen saturation

Question 12

SVC = 68%
IVC = 74%
RA = 86%
RV = 86%
LV = 95%

what’s the likely diagnosis?

Answer 12

left to right atrial level shunt

LV is 95% and SVC is 68% so there’s a 27% discrepancy which is fine

but the RA has much higher saturation than it should; it’s 86% when the SVC and IVC are 68% and 74% so that means there has to be a significant left to right atrial shunt!

Question 13

what’s the formula for pulse pressure?

Answer 13

SBP-DBP

Question 14

what is the formula for mean arterial pressure?

Answer 14

MAP = 1/3SBP + 2/3DBP

this is the normal amount of time you spend during the cardiac cycle in each phase if you have a normal heart rate

diastole shortens if you increase your heart rate

Question 15

what is the formula for stroke volume?

Answer 15

end diastolic volume (EDV) - end systolic volume (ESV)

Question 16

what is the formula for ejection fraction?

Answer 16

[end diastolic volume (EDV) - end systolic volume (ESV)]/EDV x 100

= (EDV-ESV)/EDV x 100

should get about 55% of your blood out of the ventricles with each squeeze

Question 17

what is the formula for cardiac output?

Answer 17

stroke volume x HR

= (EDV-ESV) X HR

Question 18

what is the formula for cardiac index?

Answer 18

cardiac output/body surface area

Question 19

what is the formula for systemic vascular resistance?

Answer 19

(MAP - mean right atrial pressure)/cardiac output

= [(1/3SBP + 2/3DBP)- mean right atrial pressure]/ [(EDV-ESV) X HR)]

Question 20

what is the formula for pulmonary vascular resistance?

Answer 20

(mean pulmonary artery pressure - mean pulmonary capillary wedge pressure)/cardiac output)

= (mean pulmonary artery pressure - LA pressure)/[(EDV-ESV) X HR)]

Question 21

which substances decrease pulmonary vascular resistance?

Answer 21

1. prostacyclin (prostaglandin I2)
2. NO
3. endothelian antagonist

these are all vasodilators!

the pulmonary vascular system acts the opposite of the systemic resistance

Question 22

what is pulse pressure?

Answer 22

wide pulse pressure = “bounding pulses”

pulse pressure = SBP - DBP

having a high pulse pressure is almost always due to a low DBP, not a high SBP

Question 23

what can cause a wide pulse pressure?

Answer 23

1. arteriosclerosis
2. aortic regurgitation
3. PDA
4. fever
5. anaemia

Question 24

what can cause a narrow pulse pressure?

Answer 24

1. low cardiac output (i.e. cardiogenic shock, ventricular dysfunction)
2. cardiac tamponade
3. aortic valve stenosis
4. pericardial disease

Question 25

seymour butts has a BP of 150-90, HR 60, RR 30, EDV 120 mL, ESV 50 mL

what’s his:

1. pulse pressure
2. MAP
3. cardiac output
4. ejection fraction

Answer 25

PP = SBP-DBP = 60

MAP = 1/3SBP + 2/3DBP = 50 + 60 = 110

CO = (EDV-ESV) x HR = (120-50) x 60 = 4,200

EF = (EDV-ESV)/EDV x 100 = (120-50)/120 x 100 = 58.3%

Question 26

what are the 2 phases of systole?

Answer 26

1. isovolumetric ventricular contraction

AV valves are closed and you start to squeeze your ventricles

2. ventricular ejection

when you squeeze hard enough to get enough pressure to pop open the pulmonary and aortic valves

when you’ve lost enough blood and pressure has dropped lower than the pressure in the semilunar valves, they’ll close

Question 27

what are the phases of diastole?

Answer 27

1. isovolumetric ventricular relaxation

ventricles are done squeezing, semilunar valves are closed and the ventricles are relaxing so that they can lower their pressure lower than the right atria so that the AV valves can open again during diastole

ventricular filing
2. rapid filing phase

3. passive venous filling

accounts for 90% of diastolic filling

4. active venous filling

when the atria squeeze to get that last bit of blood into the ventricle = atrial kick

Question 28

really important slide 18

Answer 28

go look at it

page 287 in first aide

35 minutes into the lecture, seriously go listen

Question 29

what does the P wave represent?

Answer 29

diastole

Question 30

what does the QRS wave represent?

Answer 30

systole

Question 31

what is S1?

Answer 31

closure of the AV valves

mitral and tricuspid valves

Question 32

what is S2?

Answer 32

closure of the semi-lunar valves

aorta and pulmonary valves

Question 33

what is physiological splitting of S2?

Answer 33

when you breath in a decrease your intrathoracic pressure even more, it encourages venous return

so the right side of the blood will get some extra blood and the P2 component will lag behind since the pulmonary valve will take just a little longer to close than the aortic valve since it has to pump out extra blood from the right ventricle

there are other things that cause increased blood flow and will cause a fixed splitting that you hear all the time because it’s a pathological problem – can be from a shunt or leaky valve like pulmonic stenosis, right bundle branch block or atrial septal defect

Question 34

what 3 things can cause pathological fixed S2 splitting?

Answer 34

1. valvar narrowing issue = pulmonic stenosis
2. conduction delay = right bundle branch block
3. volume issue = atrial septal defect

Question 35

when does S3 happen?

Answer 35

right after S2 during diastole

can be normal like in athletes and pregnant woman

may also be a sign of ventricular or systolic dysfunction –> if your ventricle doesn’t squeeze well, as soon as diastole starts you get extra sound

Question 36

when does S4 happen?

Answer 36

right before S1 during the end of diastole

tend to be pathological and suggest a stiff ventricle or diastolic diastolic dysfunction

Question 37

A previously healthy 18 yo male presents to your office with a one week history of URI symptoms. Over the last day he has had worsening fatigue, malaise and SOB. His vitals are T 101.4F, P 120, RR 30, BP 85/45. Which of the following is the most likely cardiac finding?

A. Systolic ejection murmur louder with standing

B. Diastolic murmur loudest at the apex

C. Fixed split S2

D. S3 gallop rhythm

E. S4 gallop rhythm

Answer 37

S3 gallop rhythm

BP is low, fever, high respiration

you should be worried about myocarditis which causes ventricular dysfunction!

Question 38

what is a pressure-volume loop?

Answer 38

slide 22

page 287 first aide

minute 52 lecture

Question 39

what happens if you increase heart contractility?

Answer 39

you increase the stroke volume which is how much blood the heart is pumping out with every pump and you will decrease the end systolic volume ESV since you’re squeezing more blood out

it also increases the ejection fraction since ESV is decreased

EF = (EDV-ESV)/EDV x 100

things that increase contractility and make your heart squeeze better are things like epinephrine and norepinephrine

Question 40

what happens if you increase the preload of the heart?

Answer 40

this is like if you give someone a fluid bolus!

so you will increase the end diastolic volume since you’ve filled the heart with more fluid since you gave them extra venous return

provided you don’t have any problems, you’ll squeeze out all the blood plus the extra blood from the bolus which will result in an increased stroke volume

there isn’t any increased contractility because your heart is just pumping to get back to its baseline ESV that it’s used to

Question 41

what happens if you increase the after load of the heart?

Answer 41

so what if you increase the BP or cause aortic stenosis; something that would make it harder to get blood out of the left ventricle then your left ventricle will have a harder time getting blood out

if you drive up the systemic vascular pressure for whatever reason, during the isovolumic contraction your left ventricle will have to build up a lot more pressure to get the aortic valve to open

this will cause your stroke volume to decrease because you’re spending so much time building up pressure to get the aortic valve to open that you don’t get as much blood out which also means your end systolic volume ESV will be increased since there’s more blood left

so severe HTN or aortic stenosis will increase your afterload and make it harder to get blood out –> HTN means that the ventricle has to build up more pressure to get to a higher pressure than the aorta so that the aortic valve will actually open since blood goes from high to low pressure

Question 42

squatting does which of the following?

A. Increases preload

B. Lowers pulmonary vascular resistance

C. Decrease systemic venous return

D. Decreases afterload

E. Increases contractility

Answer 42

A. increases preload

as you squat and squeeze on the blood vessels on your legs it’ll encourage blood to go back AND you’re driving up your afterload because you’re increasing your BP

so squatting increases preload AND afterload!