Define the cardiac cycle
The series of mechanical and electrical events which occur and repeat with each beat of the heart
4 phases (brief) of the cardiac cycle
Innflow of blood
Isovolumetric contraction
Outflow of blood
Isovolumetric relaxation
What does isovolumetric mean
Contraction or relaxation of the chambers with both of the valves shut, lead to no change in volume but a change in pressure is seen
What ECG wave represents atrial depolarisation
P wave
Since the SA node is found in the right atrium, does the right ventricle contract before the left atrium, why?
No both conduct simulataneously thanks to the fast conduction velocity of the impulse via Bachmans bundle
What occurs when the atria contract
Pressure in the atria increases and blood is squeezed into the ventricles
How much of the blood entering the ventricles is passive, how much is down to the contraction of the atria
80% passive, around 10% from atrial contraction
What is the contraction of the atria also known as
The atrial kick
What occurs once the atria have finished contraction
Atrial pressure falls and a pressure gradient reversal occurs across the AV valves causing the valves to float upward before closure
What occurs to the AV valves after the atria have finished contraction
Pressure gradient reversal across the AV valves causes them to float upwards before they close
At phase 1 what is maximum
The volumes of the ventricles
When do end diastolic volume (what phase)
1
What is end disastolic volume
The maximum volume of blood in the ventricles
What is LVEDV
Left ventricle end diastolic volume
What is the typical LVEDV and what does this represent
120ml
The ventricular preload
What is the ventricular preload
The intial strectching of the cardiomyocytes prior to contraction
Typical end diastolic pressure of the Lv
8-12 mmHg
Typical end diastolic pressure of the RV
3-6 mmHG
Why is the end diastolic pressure of the RV lower than the LV
Wall of the epithelium is thin in pulmonary circulation, gaps between the capillary endothelial cells to allow movement of substances.
If pressure was too high fluid would be forced through the gaps and into the lungs - would cause oedema
What does the QRS complex represent - what phase is this this the beginning of
Ventricular depolarisation, marks the start of phase 2
What is the state of all of the valves in phase 2
All of the valves are closed
What does ventricular depolarisation trigger
Excitation, contraction coupling
What can be said about dP/dt during phase 2
Maximal early in phase 2
When do the AV valves close
When the intraventricular pressure exceeds the atrial pressure
What also contracts during ventricular contraction, what does this do and prevent
Contraction of the paillary muscles, causing tension in the cordae tendinea attached to the valve leaflets. The tension in the AV valve leaflets prevent them from bulging backward and inverting
What causes the first heart sound
The closing of the AV valves
Why does the first heart sound compose of two parts? What is the gap between the two sounds
Because mitral valve closes slightly earlier than the triscuspid valve
Which side of the heart is the tricuspid
tRiscuspid RIGHT
Which side of the heart is the mitral valve
mitraL LEFT
Phase 3 is also known as
Isovolumetric contraction
What two valve movements does phase 3 occur between
The closure of the AV valves and then the openig of the pumonary/aortic valves
Because their is no change in volume, when contractign what happens
Rapid rise in pressure
During isovolumetric contraction what determines the dP/dt
Rate of contraction of the muscle fibres which is in turn governed by mechanisms governing excitation contraction coupling
What causes the c wave in LAP, when does this occur
Bulging back of mitral valve leaflets into the left atrium ==> causes the volume here to decrease slightly
What is the state of the two valves during phase 4
Aortic and pulmonary valves open
The AV valves remain closed
At what point does ejection begin
When the intraventricular pressure exceeds the pressure in the aortic and pulmonary arteries which then causes the respective valves to open
When is MAX outflow velocity reached
Early in the ejection phase
Are any heart sounds made during ejection
No opening of the healthy valves is a normally silent process
What occurs to LAP during ejection (phase 4)
Initially decreases as the atrial base is pulled downward expanding the atrial chamber
What occurs during phase 5
Isovolumetric relaxation
What phase does isovolumetric relaxation occur in
5
When do the aortic and pulmonary valves close
When the intraventricular pressure has fallen sufficiently
Does the aortic or pulmonary valve close first
Aortic closes first
What causes the second heart sound
The closing of the aortic and pulmonary valves
What is the closure of the aortic and pulmonary valve associated with
A small backflow of blood into the ventricles and a characterisic notch (dicrotic notch)
What is the rate of pressure decline in the ventricles determined by, what is this known as
Determined by the rate of relaxation of the ventriuclar muscle, known as leuistropy (rate of relaxation)
What is leuisitropy regualted by
Regulated by the sarcoplasmic reticulum which is responsible for re-sequestering Ca ions following contraction
When all of the valves have closed at the muscle is relaxing what does this cause
Decrease in pressure but no change in volume
Isovolumetric releaxation
Once the aortic valve has shut what is the volume of blood left known as, what is a typical value for this
Left ventricular end systolic volume
50ml
What is the equation for stroke volume, show how a typical stroke volume is 50 mls
LVEDV - LVESV = SV
120 - 50 = 70 mls
During isolvolumetric relaxation of the ventricles what is happening to LAP
Continuing to rise due to venous return of the blood
Phase 6 is known as
Rapid filling
Which phase is rapid filling
6
When/how does ventricular filling begin
As ventricles relax intraventricular pressure falls below the pressure in the atria this causes the AV valves to open and blood to flow into the ventricles
Why does intraventricular pressure continue to fall despite them filling
They are still relaxing
What occurs to LAP when the mitral valve opens
Rapid fall
When is the peak of the LAP, what is this called, what occurs after
Peak just before the mitral valves open known as the v wave, followed by the y-descent of the LAP
Where is a similar V and Y wave and descent seen in the body
Found in the right atrium and the jugular vein
What can be said about S3
Usually silent
What would some reasons for a sound being heard at S3 be
Tensing of the chordae tendinae or AV ring
Could be the turbulent flow of blood back into the ventricles
What occurs as the ventricles continue to fill
They become less compliant and the intraventricular pressure rises, this reduced the pressure gradient across the AV valves so rate of filling is reduced
What % of ventricular filling is passive
90%
A wave in LAP represents
Atrial systole
What is S1
Closure of the mitral and tricuspid valve, marks the end of diastole and beginning of ventricular systole
What is S2
Closure of the aortic and pulmonary valves at the end of systole
What is S3
Low pitched rapid entry of blood from the atria to te ventricles
What part of the stephoscope is S3 best heard through
The bell
