Cardiovascular Physiology Flashcards
What is a cardiac cycle?
The time for one systole and one diastole. If the HR was 80bpm then a cardiac cycle would last 0.75s
How much time is diastole and systole? How does this alter in faster HRs?
1/3 systolic 2/3 diastolic It becomes 50:50 at faster HRs to allow max time for stroke volume ejection but compromises time for diastolic filling and coronary perfusion
How does the resistance against which the left side of the heart has to eject compare to the right?
The SVR is 5 times higher than the pulmonary vascular resistance (PVR).
How does the normal peak left ventricle pressure compare to the right?
LV is 120mmHg and right is 25mmHg
What are the sequence of events following diastole?
- Isovolumetric relaxation
- Ventricular filling (Rapid -> slow (diastasis)
- Atrial systole
- Systole
- Isovolumetric contraction
- Ventricular systole
What are on the x and y axes of the pressure-time curve when describing the left ventricle pressure changes during the cardiac cycle?
X-axis = time (seconds)
Y-axis = pressure (mmHg)
What does the pressure time curve look like for the left ventricle?
What does the pressure-time curve look like for the aorta/left atrium and ECG?
Describe the events during cardiac systole and how they relate to the pressure-time changes on the graph
- atrial systole
- reflected pressure from atrial ejection into the ventricles
- MV closes
- atrial systole completes ventricular filling
- pressure in LV > LA so MV closes
- isovolumetric contraction
- both MV + AV closed, 1st stage of systole
- represents pressure generation which stops when LV pressure > aortic pressure and AV opens, sharp upstroke in pressure
- AV opens
- at 80 mmHg
- Ejection
- ventricular ejection into aorta
- AV closes
- as ejection continues, pressure falls in LV
- isovolumetric relaxation
- both MV + AV closed
- first stage of diastole
- relaxation is metabolically active
- MV opens
- MV opens as LV pressure falls below LA, passive ventricular filling commences
Describe the pressure-time changes in the aorta
- AV opens
- when pressure in LV exceeds that of aorta (80mmHg)
- Ejection
- initially rapid then slows
- AV closes
- when the LV pressure is < aortic pressure the AV closes
- pressure then falls in aorta due to diastole due to run off into vascular tree
- elastic recoil of aortic walls creates a dichrotic notch on the aortic pressure trace
Describe the pressure-time changes in the left atrium
- a wave
- atrial contraction delivering 30% of volume to LV
- c wave
- isovolumetric contraction, bulging back of MV into LA so small increase in pressure
- x descent
- as the ventricle contracts this pulls the fibrous atrio-ventricular rings towards the heart apex
- this comparitively lengthens the atria and causes pressure to fall
- v wave
- LA pressure rises due to venous return accumulating the atria throughout systole whilst the MV is closed
- y descent
- MV opens, blood flows into ventricle
- pressure in LA falls
What does AF cause on the pressure-time changes of the left atrium?
No a waves
What does tricuspid regurg look like on the pressure-time change curve of the left atrium?
- prominent v
- loss of c wave
- loss of x descent
What causes a regular cannon “a” on the pressure time curve of the left atrium?
AV junction block
What causes an irregular cannon “a” on the pressure time curve of the left atrium?
Complete heart block
What does the pressure-volume loop for the left ventricle look like?
- shows the volume of blood “moved” by the pump and how much pressure is generated to achieve this
- this represents one cardiac cycle
- volume (mls) on the x axis
- pressure (mmHg) on the y axis
- A = MV opens
- B = MV closes
- C = AV opens
- D = AV closes
- B - C = isovolumetric contraction
- D - A = isovolumetric relaxation
- stroke volume = LVEDV - LVESV
- work done = pressure x volume (area inside of loop)
What is pre-load and how does it affect the pressure volume loop of the heart?
- preload is the end diastolic stretch or tension of the ventricular wall
- signified by the left ventricular end diastolic volume on the x-axis
- at increased LV volumes the shape of the LV filling curve changes from linear to a gradually increasing gradient
- increasing preload increases SV until overdistension occurs (frank-starling relationship)
What is contractility in the heart?
The intrinsic ability of the heart to do mechanical work for a given pre- and afterload.
It’s shown by the slope of the end-systolic pressure line.
This contractility line is known as Ees.
If contractility increases then Ees has an increased slope and is therefore rotated up and to the left eg; if catecholamines administered.
What is afterload? How does this affect the pressure-volume loop?
Afterload is the ventricular wall tension required to eject the stroke volume. It is indicated by slope of straight line joining LVEDV from x-axis to the end systolic point of the loop (Ea).
If afterload increases in isolation then the gradient of line moves up and to the right.
