Haemodynamics Flashcards
Difference between serum and plasma
Plasma- fluid collected from unclotted blood
Serum- fluid collected from clotted blood
Units for flow and pressure
Flow- L/min, mL/min (for blood)
Pressure- mmHg (BP), Pascal (SI unit)
What is the equation for flow and what is the name of this law?
Flow= ΔP/R
Darcy’s law
What does K and R stand for
K- conductance (measure of ease of flow)
R- resistance (measure of difficulty of flow),1/K
Define resistance in blood flow
The difference in mean pressure needed to move one unit of flow in steady state (mmHg min/mL)
Vascular resistance
Resistance to flow in blood vessels
Describe the relationship between resistance (R) and perfusion pressure (ΔP) and flow
Flow and resistance are reciprocally related
Flow UP, ΔP UP
R UP, Δ P UP
Laminar flow and turbulent flow
Laminar flow: silent, smooth
Turbulent flow: noisy, disorganised
Sketch the graph showing the relationship between flow,resistance and perfusion pressure
Draw a sketch describing the relationship between flow and perfusion pressure in laminar and turbulent flow
3 factors creating turbulent flow
Branching of vessels
Change in direction of blood flow
Stenosis
Name the point at which turbulent flow is created
Critical Reynolds number
What is a stenosis
Abnormal discrete narrowing of an artery / open area of a heart valve
3 primary factors for flow resistance
Diameter, length of vessel, viscosity
What is the most (physiologically) important factor for determining flow resistance
Diameter
What doesn’t change resistance flow
Vessels length
Viscosity
Give an example on how size of diameter affects flow
~20% decree in radius halves the flow
List arteries, ventricle, veins etc. in order of decreasing pressure
Left ventricle
Aorta
Large arteries
Resistance vessels (small lumen diameter)
Capillaries
Venues
Veins
Vena cava
Why is the resistance in the aorta low?
Large diameter, relatively short
What contributes to the greatest component of total peripheral resistance
Smallest arteries and arterioles
Why is lower velocity useful in capillaries ?
Capillaries contain nutrients so slower flow allows absorption of nutrient
Equation for Pulse pressure (PP)
Systolic blood pressure (SBP) - Diastolic blood pressure (DBP)
Mean arterial pressure (MAP)
DBP + (SBP - DBP)/3) = DBP + 1/3 PP
At what pressure will organ perfusion be impaired ?
Below 70mmHg
Equation for ΔP (mean arterial pressure)
Mean arterial pressure - Central venous pressure (CVP)
Equation for Mean arterial pressure (MAP)
MAP= CO × TPR (Total peripheral resistance)
Define ‘pulse’
A shock wave that arrives slightly before the blood itself
How does haemorrhage and age change pulse pressure
Decreases
(Since volume decreases)
What factors increase pulse pressure ?
Elite athletes: systolic increased and diastolic decrease
Vasodilation: decreases peripheral resistance
Heart block: bradycardia
Reason: increased run off and difference in systolic&diastolic pressure
What does the principles of indirect BP measurement rely on ?
Changes in type of flow (laminar and turbulent)
What causes pathological turbulence ?
Atheroma
Stenoses vessel
What can be heard and felt over a stenosed vessel?
Heard: Bruit
Felt: Thrill
What sound do you hear when laminar flow changes to turbulent flow
Korotkoff sounds
What happens if cuff size is too small, big
Small: overestimates BP
Big: underestimate BP
At what level of the body should BP be taken
At the level of heart
What is the pressure below and above the heart?
Below level of heart: Greater P
Above: Lower P
How does postural hypotension affect blood pressure
⬇️ stroke volume
Transient arterial hypotension
Symptom: dizziness upon standing
Describe what can be hear during auscultation of the brachial artery whilst measuring BP
(Laminar & turbulent flow, systolic &diastolic pressure)
What happens to the velocity of blood through a stenosed vessel
Increases through the stenosis and turbulence occurs beyond stenosis
In between which vessel types does the greatest change in BP occur
Between arteriolar and capillaries
