CARDIAC UNIT: CARDIAC CYCLE AND METABOLISM Flashcards
Explain one cardiac cycle in terms of changing pressures and volumes
Define: pulse pressure
systolic-diastolic pressure = 40 mmHg usually
What is normal diastolic pressure?
80 mmHg
What is normal systolic pressure?
120 mmHg
Define: end systolic vol and give the normal reading
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
Define: end diastolic vol and give the normal reading
the amount of blood that is in the ventricles before the heart contracts
120 ml
Define: stroke vol and give the normal reading
End diastolic volume - End systolic volume = 70 mL
Define: ejection fraction
Give the normal and low %. When is the low ejection fraction common?
Ejection fraction: stroke volume / end diastolic volume
Normal: 55-70%
Low: <50%
Common post MI
Map the PRQST wave onto the pressure volume loop
see diagram
Define: dicrotic notch
Dicrotic notch: brief increase in aortic pressure due to closure of aortic valve and elastic recoil of aorta
Define: heart murmur
mitral valve failure
Discuss the effects of increased preload on the cardiac pressure volume relationship.
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
Discuss the effects of increased afterload on the cardiac pressure volume relationship.
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
Discuss the effects of contractility on the cardiac pressure volume relationship.
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
Compared to skeletal muscle, what % of the fuel used for heart contractions is free fatty acids?
heart: 70-90%
skeletal muscle: 5%
What fuel sources may the heart use? Which one is the primary fuel source?
- glucose
- glycogen
- even lactate
- fat - primary source
How is the heart designed for fat use?
- high expression of FABP, CAT, and mitochondria
Where does beta oxidation occur?
Mitochondria
Describe beta oxidation in a cardiomyocyte
- 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
Describe glucose metabolism in a cardiomyocyte
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
What regulates glucose metabolism in a cardiomyocyte
- 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
Describe lactate metabolism in a cardiomyocyte
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
