CVS 3 - Haemodynamics Flashcards
What is “haemodynamics”?
What dictates the delivery of blood to different organs?
What regions does blood move from and to?
- Haemodynamics is the movement of blood and the physical factors controlling blood flow.
- Metabolic demands of the body and its organs
- Blood moves from high to low pressure regions (therefore a pressure gradient is needed for blood to move)
What is serum?
How much does whole blood viscosity change?
What are changes in plasma viscosity typically caused by?
What is plasma viscosity used as an indicator for?
- Serum = plasma without clotting factors
- Whole blood viscosity changes are uncommon, but can occur in conditions such as polycythaemia and thrombocythaemia.
- Acute phase plasma proteins, e.g.: fibrinogen, or CRP. Used as an indicator of inflammation (particularly CRP)
What is “flow” and “pressure” and what are their units of measurement?
- Flow = volume transferred per unit of time - typically mL/min for blood.
- Pressure = force per unit of area - mmHg for BP.
What is Darcy’s Law? (calculation of flow)
What is it analogous to?
- Flow = Delta P/Resistance
Delta P = Pressure gradient/difference/perfusion pressure
Resistance = Difficulty of flow - Analogous to Ohm’s law (Current = Voltage/Resistance)
How are flow and resistance (vascular resistance) related to each other?
Why is this important?
- They are reciprocally related, as one goes up, the other must go down.
- This helps us to increase blood flow towards certain organs when required.
What are the 2 main types of blood flow, their features, and when do they usually occur?
1) Laminar flow - smooth, silent blood flow maintaining energy. Typical of most arteries, arterioles, venules and veins. Blood moves in concentric layers, moving fastest in the middle and slowest on the outside.
2) Turbulent flow - disorganised, noisy blood flow, where energy is lost. Occurs in changing direction of vessels (branching) or after a stenosis (narrowing of artery or open area of heart valve).
What are the 3 primary factors in resistance to flow?
Which one is the most important and why?
- Radius of vessel, Length of vessel + Viscosity
- Radius as length of vessel doesn’t change and viscosity regulated within a narrow range.
- Also because in Poiseuille’s Law (measurement of flow), radius is raised to the 4th power, so therefore has a large impact on flow/resistance. E.g.: 20% decrease in radius = 1/2 flow.
What is a drop of pressure in circulation indicative of?
Where is the largest change is resistance found?
- A change in resistance across a vessel class
- Smallest arteries and arterioles (resistance decreases across circulation, aorta has low resistance, resistance in arterioles much higher).
How does cross-sectional area change over the circulation?
How is cross-sectional area related to velocity of blood flow?
Why is this relationship important in the capillaries?
- Cross sectional area increases from arteries to capillaries (greatest in capillaries), then decreases again towards vena cavae
- Cross-sectional area and velocity inversely proportional
- Therefore, slowest velocity in the capillaries, allowing sufficient time to maximise nutrient/oxygen exchange to respiring tissues.
How is pulse pressure (PP) and mean arterial pressure (MAP) calculated and what are their normal values?
PP = SBP - DBP (difference between systolic and diastolic blood pressure) MAP = DBP + (PP/3)
- PP = 42mmHg
- MAP = 80 + (42/3) = 94mmHg (93-94 typical)
What 2 factors are MAP determined by?
MAP = CO x TPR
CO = total blood flow TPR = (mean aortic pressure -central venous pressure)/CO (but CVP is essentially 0)
What 2 things governs pulse pressure?
What causes an increase of PP during exercise?
What can PP inform us of?
1) Volume of blood ejected 2) Compliance of arterial system
- Increase stroke volume with relative compliance of vessels (as PP = sbp-dbp)
- CVS function (as CO = SV x HR)
What is “pulse”?
What does a strong/bounding pulse indicate?
When can this happen?
- A pulse is the shock wave that arrives slightly before the blood itself.
- A strong/bounding pulse = increased PP.
- In heart block/bradycardia (as EDV is lower), in vasodilation (as EDV is lower) and in elite athletes (as SBP is increased and DBP decreases).
What principle does the indirect measurement of blood flow rely on?
What can be felt and heard when turbulent flow results beyond a stenosis?
- Changes in types of blood flow (laminar and turbulent)
- Thrill can be felt, Bruit can be heard - velocity of the blood also increases
How is a cuff used to measure BP?
What are the principles behind this and what sounds result where?
- Cuff occludes brachial artery to prevent laminar flow.
- Pressure slowly released, causing turbulent flow beyond the stenosis, resulting in Korotkoff sounds.
- First sounds (tapping sound) = systolic pressure
- End of sounds = Diastolic pressure
