CARDIAC UNIT: CARDIAC CYCLE AND METABOLISM

Question 1

Explain one cardiac cycle in terms of changing pressures and volumes

Question 2

Define: pulse pressure

Answer 2

systolic-diastolic pressure = 40 mmHg usually

Question 3

What is normal diastolic pressure?

Answer 3

80 mmHg

Question 4

What is normal systolic pressure?

Answer 4

120 mmHg

Question 5

Define: end systolic vol and give the normal reading

Answer 5

the volume of blood in the left ventricle at the end of the systolic ejection phase immediately before the beginning of diastole or ventricular filling

50 ml

Question 6

Define: end diastolic vol and give the normal reading

Answer 6

the amount of blood that is in the ventricles before the heart contracts

120 ml

Question 7

Define: stroke vol and give the normal reading

Answer 7

End diastolic volume - End systolic volume = 70 mL

Question 8

Define: ejection fraction

Give the normal and low %. When is the low ejection fraction common?

Answer 8

Ejection fraction: stroke volume / end diastolic volume
Normal: 55-70%
Low: <50%
Common post MI

Question 9

Map the PRQST wave onto the pressure volume loop

Answer 9

see diagram

Question 10

Define: dicrotic notch

Answer 10

Dicrotic notch: brief increase in aortic pressure due to closure of aortic valve and elastic recoil of aorta

Question 11

Define: heart murmur

Answer 11

mitral valve failure

Question 12

Discuss the effects of increased preload on the cardiac pressure volume relationship.

Answer 12

more blood coming into the heart, increased stroke volume, greater stretch of muscle, increasing its length, and increasing its tension (remember - frank starling relationship)

Increasing end diastolic volume increases contraction

Pumping more blood but always end up with same end systolic volume

Question 13

Discuss the effects of increased afterload on the cardiac pressure volume relationship.

Answer 13

Pressure you need to generate in left ventricle needs to increase in order to overcome pressure in aorta to open aortic valve

Increased isovolumetric contraction time, early closing of aortic valve, increased end systolic volume, decreased stroke volume

Question 14

Discuss the effects of contractility on the cardiac pressure volume relationship.

Answer 14

Increased contractility, increased force contraction, increased max systolic pressure. Decreased end systolic volume, increased stroke volume

Positive inotropic state

We can squeeze more blood out!
We are super efficient

Question 15

Compared to skeletal muscle, what % of the fuel used for heart contractions is free fatty acids?

Answer 15

heart: 70-90%
skeletal muscle: 5%

Question 16

What fuel sources may the heart use? Which one is the primary fuel source?

Answer 16

• glucose
• glycogen
• even lactate
• fat - primary source

Question 17

How is the heart designed for fat use?

Answer 17

• high expression of FABP, CAT, and mitochondria

Question 18

Where does beta oxidation occur?

Answer 18

Mitochondria

Question 19

Describe beta oxidation in a cardiomyocyte

Answer 19

• albumin carries free fatty acid in the blood vessels ( 7 FFA/ albumin)
• FABP brings FFA into the cell
• 2 ATP is spent activating the FA
• Carnitine acyltransferase (CAT): brings the FFA into the miochondria
• 2-carbon actyl co-a at a time are fed into the citric acid cycle
• Oxygen is required for this process
• Reduction and oxidation of NAD and FAD is what leads to ATP production.
• Oxygen is needed at the end in electron transport chain. Without oxygen, no beta oxidation
• a single 18 carbon chain leads to 146 ATP molecules

Question 20

Describe glucose metabolism in a cardiomyocyte

Answer 20

GLUT4: insulin regulated glucose transporter moves glucose into cell
- glucose –> pyruvate –> pyruvate dehydrogenase converts pyruvate into acetyl coA in the presence of oxygen.
- in the presence of oxygen, we can produce 36 ATP
- In the absence of oxygen, pyruvate turns into lactate and we can still make ATP but only 2 ATP
- Lactate dehydrogenase: catalyzes the conversion of pyruvate to lactate and back

Question 21

What regulates glucose metabolism in a cardiomyocyte

Answer 21

• Glucose uptake is dependent on concentration gradient
  
  • Insulin increases GLUT4 expression
• high β-oxidation of FFA suppresses glucose metabolism
• ii) enzymatically – PDH vs LDH choice is determined by the presence of O2

Question 22

Describe lactate metabolism in a cardiomyocyte

Answer 22

lactate cotransporter brings either lactate or hydrogen into cell from blood.

lactate dehydrogenase generates pyruvate from lactate as needed.

pyruvate is converted into acetyl coA by pyruvate dehydrogenase and enters the krebs cycle