L3: Haemodynamics Flashcards
What is serum?
Plasma without the clotting factors
Clear yellowish liquid
Does blood viscosity changes much?
Changes are relatively uncommon
Diseases –> Polycythaemia (↑RBCs), Thrombocythaemia (↑platelets) leukaemia (↑WBCs)
Thick blood –> dry gangrene in peripheries
What causes plasma viscosity to change?
Minor changes
Typically from acute phase proteins (CRP, fibrinogen, complement)
Indicates inflammation
What does haemodynamics mean?
Movement of blood
Metabolic demand dictate flow
What causes blood to move?
Moves from areas of high pressure to areas of low pressure
Pressure gradient required for movement
Define laminar flow?
Smooth flow
Maintaining energy
Most common
Define turbulent flow?
Disorganised flow
Loss of energy
Pressure increased beyond point where it can flow linearly- flow decreases
Define flow?
volume transferred per unit time (L/min)
Define pressure?
Force per unit area (mmHg) –> in blood
Why does the flow and pressure pulsate?
To model steady flow and pressure column
What is the relationship between flow and resistance?
Inverse relationship ↑resitance ↓flow
Resistance= difficulty of flow
How are pressure, flow and resistance related?
Flow= Pressure / resistance
If resistance increases, flow the same, then pressure must increase
What affects the resistance?
Diameter, length of vessel and viscosity
Diameter- most important
Length of vessel (constant)
Viscosity (constant)
Why does the diameter have the biggest impact on resistance?
Radius raised to 4th power (simplified R= 1/r^4)
19% decrease in radius –> half the blood flow
Small changes= big impact
What causes the radius/diameter of blood vessel to change?
Vasoconstriction and vasodilation
What is the relationship between pressure and resistance?
Proportional
Change in pressure= change in resistance
What structure causes the biggest change in resistance/pressure?
Arterioles--> biggest jump in pressure across vessel class Small arteries and arterioles contribute greatest component of TPR
How does pressure and resistance change in the CVS?
Pulmonary circulation (heart to lungs) lower pressure than systemic Short and wider vessels
Longer vessel- greater resistance reduced flow
Short- resistance decrease flow increases
Increased diameter, reduced resistance
Reduced diameter, increases resistance
Define velocity?
The distance fluid moves in a given time (and direction) (cm/s)
What is the relationship between flow, velocity and radius?
(flow= volume per unit time → therefore the quicker the blood moves more flow)
Flow= Velocity x Area
Area= πr^2
therefore Velocity is inversely related to radius
F= V x r^2
flow is constant
V =1/r^2
Squeeze a hose pipe, radius decreases, velocity that water shoots out increases
How is the relationship between flow, velocity and radius demonstrated in the vasculature?
Capillaries= largest SA (radius) = slowest velocity
Allows diffusion
Large number of capillaries
What is the pulse pressure?
Systolic blood pressure - diastolic blood pressure
How is the mean arterial pressure calculated?
MAP= Diastolic blood pressure + (systolic blood pressure - diastolic blood pressure)/3) MAP = DBP + (SBP-DBP)/3 Time weighted OR MAP = CO x TPR
What is total peripheral resistance? How is it calculated
Total resistance in the systemic circulation
TPR= ( Mean aortic pressure (SBP) - central venous pressure (DBP) ) / Cardiac output
What determines pulse pressure?
(pulse pressure- pressure of the blood ejected from the heart)
Compliance of arterial system (ability to expand to accommodate increased blood volume)
Volume of blood ejected
What actually is your pulse?
Shock wave that arrives slightly before the blood itself
What causes the pulse pressure to increase?
Heart block - brachycardia–> more time in filling phase so larger volume ejected each beat (↑stroke volume)
Vasodilation –> decreased peripheral resistance so diastolic pressure will drop as more of the blood ejected out the heart (more volume to fill)
Elite athletes –> systolic increased (bigger heart muscle so increased output), diastolic decreased (more of the blood ejected out the heart)
Age and atherosclerosis –> stiffening of the vessels, reduced compliancy of vessels
To record blood pressure what features of blood flow does it rely on?
Smooth laminar flow –> silent
Turbulent flow–> noisy
What is the name of the sounds you are listening for when taking a blood pressure?
Korotkoffs sounds
What is the difference between thrill and bruit
Thrill –> felt
Bruit –> heard
Turbulent flow
Describe the basis of taking a blood pressure?
Pressure cuff–> occludes blood pressure
Release air
Sound–> turbulent flow –> Korotoff sounds –> systolic blood pressure = pressure in cuff
No sound–> laminar flow–> diastolic pressure=pressure in cuff
What is important to remember when taking blood pressure?
Cuff size –> small = over estimation, large = under estimation
Positioning of cuff
Measure both arms –> use higher as reference point
Safe comfortably, upright, legs uncrossed, feet on ground
Arm supported
Repeat –> mean taken
Taken at level of the heart
What are the effects of gravity on blood pressure?
Below level of heart–> pressure increased
Above level of the heart–> pressure decreased
Gravity maintains pressure gradient allowing blood to flow from heart to foot when standing
Pooling–> below heart
What causes dizziness upon standing?
Postural hypotension
↓ SV
transient arterial hypotension
Baroreceptors not detected change
