Session 1: Haemodynamics Flashcards
What do whole blood viscosity changes indicate?
Polycythaemia, thrombocythaemia or leukaemia.
Sludgey thick blood leading to dry gangrene in peripheries
What do minor changes to plasma viscosity indicate?
Typically from acute phase plasma proteins like fibrinogen, compliment and CRP as a result of inflammation.
This means plasma viscosity can be used to indicate inflammation. However typically measured by CRP levels.
What two main types of flow are there?
Laminar flow
Turbulent flow
What is laminar flow?
Smooth and silent flow which is going parallel. Energy is well conserved.
What is turbulent flow?
Disorganised flow with no real structure. Turbulent flow is noisy.
Why would turbulent flow occur?
Because of a narrowed blood vessel or valve.
If the pressure increase beyond which flow can match it linearly turbulent flow can occur.
This is likely to occur in ventricles and stenosed arteries.
What is flow?
Volume transferred per unit time (L/min)
What is pressure? What is it measured in?
Force per unit area measured in mmHg.
Flow = K(P1-P2) where K is conductance.
What is conductance?
Measure of ease of flow.
R = (P1-P2)/Flow or Flow = (1/R) x (P1-P2) where R is resistance.
What is resistance?
Measure of difficulty of flow and reciprocal to conductance.
Darcy’s law.
Flow = (P1-P2)/R
What happens if resistance increases and flow is still maintained?
Pressure difference has to rise.
What is the seat of total peripheral resistance?
Arterioles
Give formula for pulse pressure.
PP = SBP - DBP
SBP = Systolic blood pressure DBP = Diastolic blood pressure
Man comes in with 130mmHg over 60 mmHg.
What is his SBP?
What is his DBP?
What is his PP?
SBP = 130 mmHg DBP = 60 mmHg PP = 130 - 60 = 70 mmHg
Give formula for mean arterial pressure.
MAP = DBP + (SBP-DBP)/3 or MAP = DBP + 1/3PP or MAP = 2/3DBP + 1/3SBP
At what MAP will organ perfusion become impaired?
Below 70 mmHg
Definition of pulse pressure.
Volume of blood ejected and the compliance of the arterial system govern pulse pressure.
What will happen if there is an increase in stroke volume during exercise?
An increase in pulse pressure.
What happens to pulse pressure during haemorrhage?
It decreases
What happens to pulse pressure at age during atherosclerosis?
It increases
Formula for cardiac output.
CO = SV x HR
How does MAP relate to cardiac output?
MAP = CO x TPR MAP = SV x HR x TPR
What is a bounding pulse?
Increased pulse pressure also called strong pulse.
What causes bounding pulse/strong pulse/increased pulse pressure?
Anything which will either increase systolic pressure or decrease diastolic pressure.
Heartblock leading to bradycardia
Vasodilation leading to decreased peripheral resistance
Elite athletes with increased systolic.
In R = (P1-P2)/Flow
What does each variable signify in terms of systemic circulation?
Total flow is the cardiac output
The pressure difference (P1-P2) is mean aortic pressure (P1) minus central venous pressure CVP (P2)
R is the systemic resistance also called total peripheral resistance (TPR)
What is mean arterial pressure determined by?
Cardiac output and total peripheral resistance MAP = CO x TPR This is from TPR = (MAP - CVP)/CO Where CVP is near to 0 because it's low This leaves TPR = MAP/CO MAP = TPR x CO
Factors determining resistance to flow.
Diameter, length of vessels
Viscosity of blood
Physiologically diameter is most important.
Where is the site of resistance and why?
In arterioles and terminal arteries because they have a smaller diameter.
But capillaries have smaller diameter than arterioles. Why is resistance not higher here?
Because capillaries are connected in a parallel manner. In parallel the conductance is additive (1/R1+ 1/R2 etc…) where 1/R = K aka conductance.
What is thrill?
Change in blood flow that can be felt
What is bruit?
Change in blood flow that can be heard
Explain the process of manual blood pressure taking.
We create a turbulent flow and auscultating.
The changes from laminar to turbulent flow when you start to release pressure caused by the strap.
The changes from laminar to turbulent can be heard and are also known as korotkoff sounds.
When turbulent goes to laminar again the sound will disappear.
How do you know which is the SBP and DBP?
SBP is the pressure of which the first sound heard
DBP is the pressure of which there is no sound left
What is important to consider in blood pressure by auscultation?
Technique-wise.
Cuff size. Too small will overestimate
Too big will underestimate
Position of cuff Measure in both arms Sat comfy with legs uncrossed and flat on the ground. Arm supported Repeated several times
How does gravity affect blood pressure?
Pressure below level of heart is greater
Pressure above the level of the heart is lower.
