Microstructure and function of the heart

Question 1

What is the calculation for stroke volume?

Answer 1

SV= EDV-ESV

Question 2

What is the calculation for Cardiac output?

Answer 2

CO= HRxSV

Question 3

What is EDV?

Answer 3

End diastolic volume, volume of blood just before contraction

Question 4

What is ESV?

Answer 4

End systolic volume, volume of blood after contracition (left overs)

Question 5

What do increases in EDV do?

Answer 5

Increase in myocardial performance

Question 6

What is the length-force realtionship?

Answer 6

As EDV increases, myocardial length increases, muscle starting length increases, increasing cross bridge formation, increasing myocardial contractiliy

Question 7

What is stroke volume between?

Answer 7

Isovolumetric relaxation and isovolumetric contraction

Question 8

How does the sympathetic NS cause contraction?

Answer 8

NA and the beta-1-receptor in cardiac muscle cells

Question 9

How do hormones cause contraction?

Answer 9

Circulating A and NA

Question 10

What are some symptoms of heart failure?

Answer 10

• Crackling sound- fluid in lungs
• Edema, specifically right side oedema, edema in periphery causing a clog increases hydrostatic pressure in the lower limbs increasing pressure

Question 11

Why can myocardial infarction cause heart failure?

Answer 11

increase severity, decreased ventricular contractility and compliance

Question 12

What is compliance?

Answer 12

STRECTH

not elasticity

Question 13

What happens if there is a fall in contractility and why may this occur?

Answer 13

Smaller stroke volume as there is the same pressure buy smaller volume is ejected. this is due to the ventricle being flabby and weak. This can be due to illness

Question 14

What happens in there is a fall in compliance?

Answer 14

Stroke volume falls as the ventricle is stiff and fibrotic

Question 15

What is the ejection fraction?

Answer 15

Quantification of contraction as a percentage

EF= SV/EDV

Question 16

What is the clinical importance of ejection fraction?

Answer 16

Measure of the ability of the ventricle to contract

• > 75%- could indicate hypertrophic cardiomyopathy
• 40-55% abnormal- but may be clinically insignificant
• 40%- HF- can be very low

Question 17

What is preserved EFHF?

Answer 17

Diastoli heart failure. Heart muscles contract normally but the ventricles do not relax as they should during ventricular refilling

Question 18

What is hypertrophic cardiomyopathy?

Answer 18

Thickening of the myocardium making the lumen of the left ventricle smaller therfore less blood. the compliance of the ventricle may also reduce. Ventricles ability to relax and fill with blood is reduced.

Question 19

What is strain and why is it important?

Answer 19

The amount the muscle is stretched and it is important to the function

Question 20

What is the sinusoidal wave pattern?

Answer 20

Shows the lengthening period and shortening period. Pressure volume loops.

Question 21

What is the % where strain amplitude begins to affect power output?

Answer 21

12%

Question 22

What also happens when strain amplitude changes?

Answer 22

Passive force increases- structural proteins resist overstretching of myofibrils

Question 23

What is the length-force relationship?

Answer 23

With increased starting muscle length, increased net power. Until it reaches optimum. Then power decreases.

Question 24

What is resting HR in a man?

Answer 24

70-90bpm

Question 25

What is the theoretical max HR?

Answer 25

220

Question 26

What happens in an aged heart?

Answer 26

Left ventricular thickening, increases in cardiomyocytes size, loss of cardiomyocytes, increase in extracellular matrix, decreased oxygen consumption, decreased maximum heart rate, reduction in cardiac function, decreases in ejection fraction and decreases in responsiveness to Beta-adrenergic stimulation.