blood pressure ad haemodynamics 2 Flashcards
- Blood flow is analogous to —
– Ohm’s law: —
– pressure gradient (ΔP) = — (Q) x — (R) - Rearranging we see perfusion or flow is equal to the— over —
Q = ΔP ÷ R (this is — law) - Flow varies — with the — and — with —
electrical current
V=IR ( voltage = current x resistant )
flow x resistance
pressure gradient/resistance
Darcys law
proportionally
pressure gardient
inversely
resistance
blood flow is —
* — of blood causes laminar flow
* At the sides of the vessel, the flow is — as blood pulls on the vessel wall
– this is — ; increasing the flow increases —
– slowest flow in this outer layer, this slows flow in the next layer
* The highest velocity is at the —
– mathematically, these layers summate to give the–
* Laminar flow is –
*– is important here too
* Since small arteries have a – area to volume, most blood is near the – and there is a large effect on — – here — viscosity — flow
* In larger arteries, there are — layers and so — velocities – this diminishes the effect of –
laminar
visocity
lowest
shear stress
shear
centre
r power 4
silent
size
large
wall
flow
increased
slows
more
increased
viscosity
cross sectional area and flow:
* In a closed system, the volume of blood flowing should be —
– cardiac output =—
* Flow is the product of the — and the flow —
– flow (Q) =—
* Since size varies through the circulation, but flow is constant, flow velocity varies with —
– V = —-
* With a large area, the flow velocity in capillaries is much — than both arteries and veins
constant
venous return
cross secntional area
flow velocity
flow Q = cross sectional area A x flow velocity V or Q=AV
size
V = Q/A
slower
- Flow is – and approximately – L/min – which is the same as — cm3/sec
- For the aorta, with an area of ~ – cm2 this is – V=Q/A V=100/5 V=20cm/sec
- For the capillaries with an area of ~ — cm2 this is – V=Q/A V=100/2000 V=0.05cm/sec
– this slow velocity — time for nutrient exchange - For the vena cava with an area of ~ – cm2 this is – V=Q/A V=100/7.5 V=13.3cm/sec
constant
6
100
5
2000
increases
7.5
non laminar flow aka turbulence:
* At — velocities flow can become turbulent – or at — diameters (see bronchial breathing)
* Under normal conditions, non-laminar flow tends to occur in the —and around— points
– narrowed points where velocity —
* Unlike laminar flow, turbulent flow is —:
– the basis of Korotkoff sounds in measuring BP
– the basis of bruit in atheroma
– the basis of heart murmurs in either stenotic or incompetent valves – and also bronchial breathing (in respiratory module)
high
large
ascending aorta or branch
increases
not silent
- Blood flow in — and —
- When it is not it indicates obstruction or other problem creating — and an — change in blood –
silent and laminar
obsctrucion
turbulence
audible
blood flow
- Primary function of the cardiovascular system is —
– delivery of – , — & —
– removal of — products - Textbook cardiac output of ~ – L circulating continuously
– roughly 7,500 L/day from approx. 100,000 heart beats
– for a normal adult at rest, it takes under – minute for a red blood cell to
circulate
bulk transport
02 nutrients and water
metabolic waste
5
one minute
*Flow is determined by Q= —
– that is to say— divided by —
* From this we can substitute for the whole system
– CO= —
– cardiac output (CO)
– mean arterial pressure (MAP)
– total peripheral resistance (TPR)
* So a circulation with low resistance does not require a — pressure to maintain flow
– alternatively you could argue a circulation with a low pressure needs a–
resistance
Q=ΔP÷R
pressure
resistance
MAP/ TPR
high
low
- Pressure is generated in the heart during —
- Cardiac output determines — pressure
– increased CO will — systolic pressure - Vascular resistance leads to pressure — across the system
- Pressure drops across the vascular tree
– aorta — > —- mmhg
– capillaries – — mmhg - great veins - — mmhg
systole
systolic pressure
increase
drops
100
25
2
- Across the vascular tree the biggest pressure drop (and therefore the biggest site of resistance) is in the — and —
- Vascular resistance is influenced by a number of factors
- Resistance to flow through a cylinder is described by — Law
- R=ηL/r4
– η is — , L is length and r is vessel radius
– in real terms, neither viscosity nor length vary greatly so — is the prime
determinant
small artries and arterioles
poisuillie law
visocity
radius
- Resistance is — l to the — of the – – R= –
- This means that small changes in vessel diameter (and thus radius) have — effects on resistance and subsequently flow
- If resistance is inversely proportional to the fourth power of the radius…then flow is — to the fourth power of the radius
inversely proportional
fourth power
radius
R = 1/r power 4 (ml/min)
larger
proportional
- This shows why resistance is in those small arteries and arteriole
- Large elastic conductance arteries have — capacity to vary diameter unlike small muscular arteries and arterioles
– the size of conduit arteries mean they offer – resistance - An increase in diameter of — will increase flow by more than —
– for the aorta with radius of 1 cm, this is a – cm increase
– for an arteriole with a radius of 0.01 cm this is only a – cm change - Since the aorta is – larger than an arteriole – 1004 = 100,000,000 greater resistance
limited
little
20%
double
0.2 cm
0.002 cm
100x
- Viscosity is proportional to — and therefore inversely proportional to —
- The thicker the solution the – the flow – just think of a particularly thick milkshake
- Blood is ~2.5 – –x more viscous than water and is due to the presence — and — cells
– both the concentration and type of plasma protein
– for red cells this is the haematocrit (HCT): the proportion of — occupied by – cells
– usually expressed as a — , typically around –% - females 37-47% and males 40-54%
resistance
flow
less
3x
plasma proteins and red cells
blood volume occupied by red cells
percentage
40%
check slide 62,63 so important
factors affecting viscosity:
* Generally blood viscosity does not change acutely
* The — will affect viscosity
– anaemia (– HCT) would — , polycythaemia (— HCT) would — viscosity
* Capillaries and smaller vessels (<300 μm) tend to have (slightly) – haematocrit due to – accumulation
– red cells are in the centre of flow, so branches get relatively more plasma to red cell (Fahraeus-Lindqvist effect)
* However flow is not greater in smaller vessels:
– r4 has much more effect on – than –
– it is just slightly faster than it would expected
haemocratitc
low
decreases
high
increases
lower
axial
flow than n
summary:
- Poiseuille’s Law: Flow = ΔP x πr4 ÷ 8ηL
- Pressure gradient (ΔP)
- Size of the blood vessel – length (L) and radius (r)
- Viscosity of the blood (η)
– haematocrit, plasma proteins and temperature
