Cardiovascular - Electrical and Mechanical events Flashcards
What is the intrinsic conduction system?
How the heart makes itself beat (via pacemaker cells)
How does extrinsic innervation affect the intrinsic conduction system?
It either increases or decreases the conduction system
Why can the heart beat independent of the brain?
Due to the electrical impulses (action potential) generated by the SA nodes
Where are the SA nodes located?
Right atrium
Where is the AV (atrioventricular) node located?
Right Atrium
What is the patway of the impulses generated by the SA node?
- Travels to left atrium
- Travels down to AV node, where it pauses
- Then travels to the Bundle of his
- The bundle branches then conduct the impulse through the interventricular septum
- Impulse then travels up the Purkinje fibres (subendocardial conducting network) which depolarises the contractile cells of both ventricles
How do sympathetic nervous impulses affect heart rate?
Increases heart rate
How do parasympathetic nervous impulses affect heart rate?
Decrease heart rate
What other factors affect heart rate?
- Age
- Wellbeing/Health/Fitness
- Stress
- Temperature
- Gender
What is ECG?
- Electrocardiogram
- Composite of all action potentials generated by nodal and contractile cells at any given time
Essentially a graphical representation of the the cardiac conduction system
What is the ECG process?
- P Wave - Atrial depolarisation
- Q R S complex - Ventricular depolarisation
- T Wave - Ventricular repolarisation
What process is not seen on an ECG tracing?
Atrial repolarisation (it does occur but is masked by the QRS Complex)
What are the mechanical events of the heart?
- Cardiac cycle
- Diastole
- Systole
- Heart sounds
- Cardiac output
What does Systole refer to?
Contraction
What does Diastole refer to?
Relaxation
What are the events occuring in the heart during the cardiac cycle?
- Ventricular filling
- Atrial contraction
- Isovolumetric contraction phase (no movement of blood, pressure building)
- Ventricular ejection phase
- Isovolumetric relaxation
What is the average heart beat amount per minute?
75
What is the length of the cardiac cycle for someone with an average heart beat rate of 75 per minute?
0.8
(60 / 75)
- Atriole Systole accounts for 0.1 seconds
- Ventricular systole accounts for 0.3 seconds
The remaining 0.4 is a period of total heart relaxation, and is called the ‘Quiescent period’
What causes heart sounds?
Closing of the heart valves
- First sounds - (lub) occurs as AV valves close and signifies the beginning of ventricular systole
- Second sound (dub) when SL valves close at the beginning of ventricular diastole
What is stroke volume?
- The volume of blood pumped out by each ventricle with each heart beat - it is correlated with the force of contraction
What is Cardiac Output (CO)?
- The amount of blood pumped by a ventricle in one minute - it is the product of heart rate and SV (stroke volume)
What unit of measurement is used for CO?
Ml/min
How do you work out SV?
end diastolic volume - end systolic volume
What is preload?
The amount the ventricles are stretched when filling with blood, and is a critical factor in determining SV
