Cardiovascular strand: Lecture 7 - cardiac haemodynamics

Question 1

If an elderly lady comes into A&E claiming she is breathlessness, cannot lie flat, her oxygen saturations have dropped and her respiration is fast and shallow, what might be wrong with her?

Answer 1

Fluid in the lungs

Pulmonary oedema (shown on X-ray)

Fuzziness - fluid

Question 2

What is pulmonary oedema?

Answer 2

fluid accumulation in the tissue and air spaces of the lungs

Question 3

Draw a graph of the changes in LV, LA and Aortic pressure during respiration, and label each point

Answer 3

Question 4

What does the graph of an action potential in non-pacemaker cells look like? Include labels

Answer 4

Question 5

What are desmosomes?

Answer 5

desmosomes stick the cells together so they’re electrically linked

Question 6

Draw a diagram of a muscle fibre (with labels) and a myofibril

Answer 6

Question 7

What happens during phase 2 of the non-pacemaker action potential?

Answer 7

increased permeability to Ca2+

decreased permeability to K+

Lots of calcium outside the cell that all move in

this calcium is used to help start a new cardiac contraction

Question 8

What is actin wrapped up in?

Answer 8

tropomyosin and troponin

Question 9

Explain how a muscle contraction is carried out (6 steps)

Answer 9

1. Ca2+ binds to troponin
2. Induces conformational chnage in troponin-tropomyosin complex
3. Exposes the binding site of actin
4. Mysosin head can then bind to actin. This requires ATP
5. Myosin exerts “pulling” action on actin
6. Initiates muscle contraction - myofilament shortens

Question 10

How much ATP do myocardial cells usilise a day?

Answer 10

6 kg

Question 11

How is maximum ejection of blood from heart achieved?

Answer 11

longitudinal filament shortening - horizontal and circumferential thickening

reduces LV chamber diameter and causes further ejection

Cells are different shapes so they contract different ways

There is horizontal, longitudinal and twisting contraction

Question 12

Who discovered about blood circulation in the heart?

Answer 12

William Harvey

Question 13

In what situations does the heart need to cope with higher demands?

Answer 13

• exercise
• intercurrent illness
• fluid overload
• pregnancy

Question 14

What is cardiac reserve?

Answer 14

The capacity to augment performance on demand

Question 15

How do we calculate cardiac output?

Answer 15

Cardiac output = heart rate x stroke volume

cardiac output - volume pumped out per min

heart rate - number of beats per min

stroke volume - volume pumped out per beat

Question 16

How do we calculate cardiac reserve?

Answer 16

Cardiac reserve = maximal cardiac output - cardiac output at rest

Question 17

How does sympathetic innervation increase heart rate?

Answer 17

• Speeds up SA node depolarisation
• More frequent action potentials
• Increases conduction through AV node/ bundle

Question 18

How can we augment stroke volume?

Answer 18

• sympathetic innervation
• prolonged opening of Ca2+ channels
• enhances calcium action in excitation/contraction coupling mechanisms

Question 19

What is stroke volume dependant on?

Answer 19

PRELOAD

Question 20

What is the difference between length-tension relations between cardiac and skeletal muscle?

Answer 20

Cardiac has a much narrower range

So you don’t have to stress it very much to get a big increase in tension

But its also sensitive to too much tension

In health, you should always be in the upwards part of the curve for cardiac muscle

Question 21

Explain how increasing preload increases cardiac performance?

Answer 21

• small changes in cardiac sarcomere length results in large variations in tension
• so stretching the LV will aid contraction
• LV end-diastolic volume (or pressure) determines how stretched the LV wall is

Question 22

What is Starling’s law of the heart?

Answer 22

“the same as the law of muscular tissue in general, that the energy of contraction however measured, is a function of the length of the muscle fibre”

Question 23

What is end diastolic volume/ pre-load ?

Answer 23

Volume of blood in the right and/or left ventricle at end load or filling in (diastole) or the amount of blood in the ventricles just before systole

Question 24

What is the relationship between stroke volume and end-diastolic volume? (graph)

Answer 24

the more you put in, the more you get out (because actin-myosin are closer together as sarcomere stretched, more myosin can bind to actin, more contraction)

but this is up to a certain point

THE FRANK STERLING CURVE

Question 25

Explain how venous return is ALWAYS correlated with CO?

Answer 25

• equilibriates right and left heart output e.g LV CO= RV preload and vise versa
• exercise and other demains cause increase venous return
• which allows augmentation of stroke volume
• so equilibrium is maintained

Question 26

When can the Frank Sterling curve shift?

Answer 26

left shift - exercise, pharmalogical stimulation (stroke volume > preload)

right shift - myocardial loss, pharmacological depression (preload > stroke volume)

Question 27

How does sympathetic stimulation of the heart work? Which way does the Frank-Sterling curve shift when this occurs?

Answer 27

• noradrenaline and adrenaline stimulate cAMP
• more Ca2+ enters cell
• greater cross bridge linking in sarcomeres

curve shifts to the left

Question 28

What is ejection fraction and how is it calculated?

Answer 28

The proportion of blood ejected out of the heart related to how much was there in the first place

ejection fraction = stroke volume / end diastolic volume

av at rest is 65-75%.

increases during exercise, decreases if heart failure

Question 29

What happens if myocardium becomes diseased?

Answer 29

It contracts less

Question 30

What does ischaemia do to myocardium?

Answer 30

causes it to scar/die

Question 31

What effect do viral infections/ alcohol have on the heart?

Answer 31

wall thinning

Question 32

What is heart afterload?

Answer 32

Afterload is the pressure the heart must work against to eject blood during systole (ventricular contraction).

Question 33

When might a patient have increased afterload/ chronic high -output

Answer 33

High blood pressure

Question 34

Which two systems are activated when a ventricle fails?

Answer 34

• sympathetic nervous system overactivates
• renin-angiotensin-aldosterone system

These measures raise the preload

Question 35

When do we move to the descending limb of the sarcomere tension curve?

Answer 35

when heart stretches

eventually, LV stretch exceeds physiological levels

Question 36

How do we treat excess fluid in the lungs?

Answer 36

• give oxygen to maximise alveolar ventilation
• morphine to relax her pulmonary vessels and reduces her preload and takes the strain of the LV
• furosemide - take fluid off her lungs (loop diueretic)