Lecture 2 - Cardiac Cycle Flashcards
What are the two phases of the cardiac cycle and what do they mean?
Systole - Contraction
Diastole - Relaxation
What are the different stages of the cardiac cycle?
Diastole 1 – Isovolumic Relaxation
Diastole 2 – Ventricular Filling
Systole 1 – Isovolumic Contraction
Systole 2 – Ventricular Ejection
What happens during Diastole 1 – Isovolumic Relaxation?
All valves shut
No change in ventricular volume
Minimal ventricular volume (end-systolic volume)
Relaxation of ventricles
Atrium fills with blood
Atria pressure increases until >ventricular pressure
What happens during diastole 2 - ventricular filling?
When atrial pressure> ventricular pressure AV opens passively
Ventricular filling
90% filling passive
Last 10% from atrial contraction
What happens during systole 1 - isovolumic contraction?
Ventricles filled
Ventricular depolarisation
Ventricle contracts
Ventricular pressure rises
AV valve closes so all valves shut
What happens during systole 2 - Ventricular Ejection?
ventricular pressure> aortic pressure
aortic valve opens
blood into aorta
What is the cardiac cycle?
The cardiac cycle is a series of mechanical events which associates temporally with electrical and valvular events.
What happens to ventricular volume during isovolumic relaxation?
Constant
What happens to ventricular volume during ventricular filling?
Rapid during early stages and slow during late stages (besides top up after atrial contraction). At this stage we have maximum ventricular volume (end of diastole volume – EDV).
What happens to ventricular volume during isometric contraction?
Constant
What happens to ventricular volume during ventricular ejection?
Decrease in volume, rapid in early stages, slower in later. At end of stage we have lowest ventricular blood volume (end-systole volume - ESV)
What happens to ventricular pressure during diastole?
Minimum at beginning but slight rise during ventricular filling and after atrial contraction.
What happens to ventricular pressure during systole?
Rapid rising during isometric contraction. Continues rising to maximum during ejection phase. Falls late systole to prepare for diastole.
What happens to arterial pressure during diastole?
Continues to fall until minimum
Minimum at end of diastole/during isovolumetric contraction
(Diastolic blood pressure)
What happens to arterial pressure during systole?
Rises to max
LVP > AP valves open
Rises to a maximum
(Systolic blood pressure)
LVP < AP valve closes
Why do we have the aortic notch/dicrotic notch/incisura?
Aortic valve closing
What happens when we miss 1-2 heart beats?
No problem
What happens when we miss 5-10 heart beats?
unconscious
What happens when we miss 5 mins of heart beats?
Clinical help - damaged heart
What happens when we miss >10mins of heart beats?
Death
Describe Diastole 1:
- Timing
- Valves
- Event
Diastole 1 0.05s
- All valves shut
Isovolumetric Relaxation
Describe Diastole 2:
- Timing
- Valves
- Event
Diastole 2 0.6s
- AV valves open
- Ventricular Filling, Atrial “top-up”
Describe Systole 1:
- Timing
- Valves
- Event
Systole 1 0.05s
- All valves shut
- Isovolumetric Contraction
Describe Systole 2:
- Timing
- Valves
- Event
Systole 2 0.3s
- SL valves open
- Ventricular Ejection
What is the function of the heart valves?
Preventing the back flow of blood
What are our two types of heart valves?
We have two types of valves which are AV (atrioventricular) and semilunar.
How many valves do we have in the heart?
4
Where are the AV valves located?
The AV valves exist between the atria and ventricles
When do the AV valves open?
When pressure in the atria exceeds that of the ventricle.
When do the AV valves close?
When the pressure of the ventricles are filled and pressure increases, the AV valve closes.
What is the first heart sound?
Closure of AV valves (M1-T1)
Low, long sound (lub)
Where are the semilunar valves?
The semilunar valves exist between ventricle and either the aorta or pulmonary artery (depending on what side of the heart)
When do the semilunar valves open?
The semilunar valves open when pressure in the ventricle exceeds the aorta or pulmonary artery.
When do the semilunar valves close?
When ventricular decreases below aortic (or pulmonary artery) pressure, the semilunar valves shut
What are the left ventricular volumes (at rest)?
End-diastolic volume (EDV) 130 ml
End-systolic volume (ESV) 60 ml
Stroke volume (SV): EDV-ESV 70 ml
Ejection fraction is: 55 - 60%
What is the difference in pressure between the left and right sides of the heart?
RV and pulmonary artery (PA) pressure are
lower than LV pressure and aortic pressure
What is the difference in resistance between the left (systemic) and right (pulmonary) sides of the heart?
Pulmonary resistance is lower than total peripheral resistance (systemic circulation)
What system does the left side of the heart send blood to?
Systemic circuit
What system does the right side of the heart send blood to?
Pulmonary circuit
What is the RV and PA pressures (at rest)?
Diastole Systole
RV pressure 0/1 25 mmHg
PA pressure 8 25 mmHg
What is the second heart sound?
Closure of semilunar valves (A2-P2)
Short, high pitch (dub)
What is the third heart sound?
Passive ventricular filling, early diastole
Heard in the young
What is the fourth heart sound?
Ventricular filling following atrial contraction
Reduced ventricular compliance
What are the effects of heart rate on cardiac cycle?
When we increase heart rate, the durations of diastole and systole decrease. However, although both events decrease, diastole shortens the most.
The higher the heart rate, the faster the filling and ejection of blood but SV stay constant.
What event occurs during the P Wave in ECG?
P Wave: Atrial depolarisation precedes atrial contraction
What event occurs during the QRS complex in ECG?
QRS Complex: Ventricular depolarisation
precedes ventricular contraction
What event occurs during the T Wave in ECG?
T Wave: Ventricular repolarisation/Ventricular relaxation
What is avg HR and cardiac at rest?
60bpm, cardiac cycle 1s
What are the timings of diastole and systole at rest?
Diastole: 0.66 s 2/3 cardiac cycle
Systole: 0.34 s 1/3 cardiac cycle
What are the timings of diastole and systole at max HR?
Diastole: 0.13 s 1/3 cardiac cycle
Systole: 0.20 s 2/3 cardiac cycle
What happens with the duration of systole and diastole when heart rate increases?
A. Systole and diastole shorten equally
B. Systole stays constant, and only diastole shortens
C. Only systole shortens, and diastole stays constant
D. Both shorten, with diastole more than systole
D. Both shorten, with diastole more than systole
