Cardiovascular strand: Lecture 7 - cardiac haemodynamics Flashcards
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?
Fluid in the lungs
Pulmonary oedema (shown on X-ray)
Fuzziness - fluid
What is pulmonary oedema?
fluid accumulation in the tissue and air spaces of the lungs
Draw a graph of the changes in LV, LA and Aortic pressure during respiration, and label each point
What does the graph of an action potential in non-pacemaker cells look like? Include labels
What are desmosomes?
desmosomes stick the cells together so they’re electrically linked
Draw a diagram of a muscle fibre (with labels) and a myofibril
What happens during phase 2 of the non-pacemaker action potential?
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
What is actin wrapped up in?
tropomyosin and troponin
Explain how a muscle contraction is carried out (6 steps)
- Ca2+ binds to troponin
- Induces conformational chnage in troponin-tropomyosin complex
- Exposes the binding site of actin
- Mysosin head can then bind to actin. This requires ATP
- Myosin exerts “pulling” action on actin
- Initiates muscle contraction - myofilament shortens
How much ATP do myocardial cells usilise a day?
6 kg
How is maximum ejection of blood from heart achieved?
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
Who discovered about blood circulation in the heart?
William Harvey
In what situations does the heart need to cope with higher demands?
- exercise
- intercurrent illness
- fluid overload
- pregnancy
What is cardiac reserve?
The capacity to augment performance on demand
How do we calculate cardiac output?
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
How do we calculate cardiac reserve?
Cardiac reserve = maximal cardiac output - cardiac output at rest
How does sympathetic innervation increase heart rate?
- Speeds up SA node depolarisation
- More frequent action potentials
- Increases conduction through AV node/ bundle
How can we augment stroke volume?
- sympathetic innervation
- prolonged opening of Ca2+ channels
- enhances calcium action in excitation/contraction coupling mechanisms
What is stroke volume dependant on?
PRELOAD
What is the difference between length-tension relations between cardiac and skeletal muscle?
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
Explain how increasing preload increases cardiac performance?
- 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
What is Starling’s law of the heart?
“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”
What is end diastolic volume/ pre-load ?
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
What is the relationship between stroke volume and end-diastolic volume? (graph)
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
