Control Of Cardiac Output Flashcards
What is total peripheral resistance?
The resistance to blood flow caused by all the systemic vasculature
What is afterload?
The load the heart must eject blood against (roughly equivalent to aortic pressure)
What is preload?
The amount the ventricles are stretched in diastole
Is related to EDV or central venous pressure
What is the pressure of the RA?
0-4mmHg
Pressure RV
25/4
Pressure of PA
25/10 mmHg
pressure LA
8-10mmHg
Pressure LV
120/10 mmHg
Pressure Aorta
120/80mmHg
What is compliance?
The amount the ventricle walls stretch increases with pressure- can be increased or decreasd in disease states
What is frank starlings law?
The higher the venous pressure the more the heart fills
What is the intrinsic control mechanism?
The more the heart pumps out means that the higher the pressure blood it will recieve into the RV which will stretch more so keeping up with the LV
What is typical stroke volume of a 70kg man?
70 ml
How much of the EDV is the stroke volume?
67%
CO=?
SV*HR
SV=?
EDV-ESV
What is blood a mixture of? What does it behave like?
A mixture of cells and plasma but behaves like a fluid
Why does blood slow down at the peripheries?
It is colder so is more viscous
What is turbulent flow?
Blood flows in all directions and continually mixes
When does turbulent flow occur?
Rate of blood flow becomes too great Blood passes by an obstruction Blood makes a sharp turn Blood passes over a rough surface Increased resistance to blood flow
What is laminar flow? What is special about the way the blood flows?
Each layer of blood remains the same distance from the wall- the centre is the fastest as there is the least resistance so there is a parabolic curve
How does the descending aorta pressure change with time?
Systolic uptake- rapid rise Peak systolic pressure Systolic decline Dicrotic notch- caused by elastic recoil of aorta End diastolic pressure
Pulse pressure=?
Peak systolic pressure- end diastolic pressure
Commonly 120-80= 40mmHg
How can mean arterial pressure be estimated?
Below what value is organ perfusion impaired?
Diastolic pressure+ 1/3 pulse pressure.
If MAP falls below 70 then organ perfusion is impaired
What is retrograde flow?
Blood in arteries flows backwards briefly during diastole and is greatest when TPR is high
What is the pulse?
A shockwave that arrives slightly before the blood itself
What is strength of the pulse determined by?
Force of ejection from LV
Therefore reduced pulse strength results from LV failure, aortic valve stenosis, hypovolaemia
Pulse pressure
What is a weak pulse often described as?
Thready
What effect does bradycardia have on pulse pressure?
Increases time in diastole so end diastolic pressure is lower so pulse pressure is greater
What effect does a decreased peripheral resistance have on pulse pressure?
Pressure falls more rapidly so end diastolic volume is less so pulse pressure is larger
What are the 7 stages of the cardiac cycle?
Atrial systole Isovolumetric contraction Rapid ejection Reduced ejection Isovolumetric relaxation Rapid filling Reduced filling
How much of the ventricular filling does atrial systole account for?
10%
How is atrial systole represented on the ECG?
The p wave
On the wiggers diagram which wave does atrial systole cause?
The a wave
What happens after atrial systole?
AV valves close- this causes S1.
This closing causes a c wave in the atrial pressure curve
What comes after atrial systole? What does this cause pressure wise?
Isovolumetric contraction
Causes a rapid rise in intraventricular pressure
How is isovolumetric contraction represented on the ECG?
The QRS complex
What happens after isovolumetric contraction?
Aortic/ PV open
What happens after the aortic and pulmonary valves open?
Rapid ejection- rapid decrease in ventricular volume as blood is ejected into the aorta
What effect does rapid ejection have on the atrial pressure on the WD?
D descent- atrial base is pulled downward as ventricle contracts
What is happening as during rapid ejection?
Blood is flowing into atria from venous inputs
What follows rapid ejection?
Reduced ejection- ventricles start to repolarise
How is reduced ejection shown on the ECG?
The T wave
What effect does repolarisation of the ventricles have on muscle tension?
Repolarisation leads to a decline in tension
What is happening to atrial pressure during reduced ejection?
It is gradually rising due to continued return from venous supply
This creates the V wave on the WD
How is the aortic valve made to close?
Ventricular pressure falls below aortic pressure which causes a brief backflow of blood
This makes the sound S2
What phase follows reduced ejection
Isovolumetric relaxation- rapid decline in ventricular pressure but volume is constant as all valves are closed
How is the dicrotic notch created ?
Is created during isovolumetric relaxation phase as aortic valve closes
What happens to make the AV valves open? What effect does the opening of these have on atrial pressure?
IV pressure falls below atrial pressure so AV valves open which causes Y descent in atrial pressure
What phase follows isovolumetric relaxation? What sign of pathology can sometimes be heard in this phase?
Rapid filling
S3 heart sound
What is diastasis? Which phase of the cardiac cycle does this occur?
Reduced filling stage- Rate of filling slows down as the ventricle reaches its inherent relaxed volume- further filling is driven by venous pressure and atrial contraction
