S2 Cardiac Cycle Flashcards
(39 cards)
Is systemic or pulmonary circulation high pressure?
Systemic circulation is high pressure (pulmonary circulation is low pressure)
What is systole?
Contraction and ejection of blood from ventricles
What is diastole?
Relaxation and filling of ventricles
What is normal stroke volume at rest?
About 70ml blood per beat
When measuring blood pressure, what part of the heart is measured?
Aorta (normal BP is 120 systole/80 diastole)
Which side of the heart has the higher blood pressure?
The left side
At a heart rate of 70bpm, how many litres of blood are pumped per minute?
About 4.9L (average human body has 5L blood)
How long is a cardiac action potential?
Longer than skeletal muscle and neuronal action potentials - about 280ms
Describe cardiac muscle…
- interconnected electrically by intercalated discs
- cells contract in response to an action potential (AP)
- AP causes a rise in intracellular Ca2+
- slower AP
- striated muscle
What are the four valves in the heart?
- Tricuspid valve (R)
- Mitral valve (L)
- Pulmonary valve (R)
- Aortic valve (L)
When do the heart valves open/close?
Open/close dependent on differential blood pressure (BP) on each side
E.g. mitral valve opens if higher BP in L atrium and close when higher BP in L ventricle
What prevents prolapse/inversion of the mitral and tricuspid valves?
Papillary muscles (attached to the heart wall) via chordae tendineae (‘strings’ connecting the papillary muscles to the valve)
Why do you want to prevent prolapse of valves in the heart?
To prevent regurgitation of blood (blood going backwards)
How is does a conduction signal cause contraction in the heart?
- Pacemaker cells in the SAN generate an action potential (AP)
- Activity spreads over the atria (atrial systole)
- The AP reaches the AVN and is delayed (for about 120ms)
- The the AVN, excitation spreads down the septum between ventricles
- Then spreads through ventricular myocardium (heart muscle) from inner to outer (endocardial to epicardial)
- The ventricle contracts from the apex up which forces blood through the outflow valves (aortic/pulmonary valves)
What are the 7 phases of the cardiac cycle?
- Atrial contraction
- Isovolumetric contraction
- Rapid ejection
- Reduced ejection
- Isovolumetric relaxation
- Rapid filling
- Reduced filling
Which side of the heart is a Wiggers diagram usually plotted from?
The left (if using the right, the pattern would be the same but at a lower pressure)
What happens in atrial contraction (Phase 1)?
- the atrial pressure rises due to atrial systole (contraction and ejection) - A wave in L atrial pressure curve
- atrial contraction accounts for last 10% of ventricular filling, the rest fills passively (down pressure gradient)
- onset of atrial depolarisation - P wave in ECG
AP
What happens in isovolumetric contraction (phase 2)?
- mitral valve closes as intraventricular pressure exceeds atrial pressure - C wave in L atrial pressure curve and closing of valve causes the first heart sound, S1
- there’s a rapid rise in ventricular pressure as ventricle contracts
- no change in ventricular volume (all valves are closed)
- onset of ventricle depolarisation - QRS complex in ECG
C
QRS
S1
What does isovolumetric mean?
No change in volume
What happens in rapid ejection (phase 3)?
- ejection begins when intraventricular pressure is higher than aortic pressure, which causes the aortic valve to open
- atrial pressure initially decreases as the atrial base is pulled downward as the ventricle contracts - X descent in L atrial pressure
- rapid decrease in ventricular volume as blood is ejected into the aorta
*blood continues to flow into the atria from the venous inputs
X
What happens in reduced ejection (phase 4)?
- ventricle repolarises and so tension decreases and the rate of ejection starts to fall - T wave in ECG
- atrial pressure starts to rise due to continued blood supply from venous input - V wave in L atrial pressure
TV
What happens in isovolumetric relaxation (phase 5)?
- intraventricular pressure drops below aortic pressure, small backflow of blood causes aortic valve to close - dicrotic notch in aortic pressure, closure of aortic and pulmonary valves produces heart sound, S2
- rapid decline in ventricular pressure, volume remains constant as all valves are closed
How do you calculate stroke volume?
What is the norm?
End Diastolic Volume (EDV) - End Systolic Volume (ESV)
About 70-80ml
When do you get the EDV and ESV?
EDV - atrial contraction (L ventricular volume in phase 1)
ESV - in isovolumetric relaxation (L ventricular volume in phase 5)
