Haemodynamics 1 Flashcards
What are Haemodynamics?
Physical factors that control blood flow
What is serum?
Plasma without clotting factors
What are the 4 components of whole blood?
- RBC
- WBC and platelets (Buffy coat)
- Plasma
What is viscosity?
- Thickness and stickiness of blood
- Resistance of fluid against flow
When does whole blood viscosity change?
What does the changes result in?
- Doesn’t change very much in healthy individuals
Changes seen in:
- Polycythaemia (RBCs)
- Thrombocythaemia (platelets)
- Leukaemia (WBCs)
You get sludgey, thick blood, leading to dry gangrene in peripheries - coagulative necrosis due to lack of blood supply
When does plasma viscosity change?
- Minor changes to plasma viscosity regularly occur
- Typically from acute phase plasma proteins (fibrinogen, compliment, C-Reactive Protein)
What is CRP?
- C reactive protein, used as a marker of inflammation
- Also an opsonin
What is flow? Units?
Volume transferred per unit of time (L/min) or mL/min usually for blood
What is pressure?
Units? Significance in blood?
Force per unit area (mmHg - millimetres of mercury to measure BP) - SI unit is pascal
Blood moves from high (artery) —> low pressure (veins)
Calculating flow
Flow = pressure change / resistance (resistance is 1/K where K is measure of conductance)
OR
Conductance x change in pressure
What is resistance?
Measure of difficulty of flow - reciprocal/opposite of K = 1/K (conductance)
How do you calculate resistance?
What is resistance to flow in blood vessels known as?
What happens if this resistance increases?
Resistance = pressure change / flow
- Vascular resistance
If vascular resistance increases:
- Pressure increases
- Flow decreases
What is the triangle for flow, resistance and pressure change?
Laminar flow vs Turbulent flow
Laminar: (4)
- Smooth
- Silent
- Maintains energy
- Moves in stream lines
Turbulent: (3)
- Disorganised
- Noisy
- Energy lost
What is the typical blood flow of most arteries, arterioles, venues and veins?
Laminar flow
Why does turbulent blood flow occur?
What do you call this?
Pressure is increased beyond point which flow can match it linearly - Reynold’s number
Where does turbulent flow occur in the body?
- Changing direction of vessels (branching vessels)
- Stenosed arteries
- Stenotic heart valves
What is stenosis?
Abnormal discrete narrowing of an artery or open area of a heart valve
State the primary factors contributing to resistance of flow
Which is the most important factor physiologically?
How come?
Diameter, length of vessel, viscosity (3)
Diameter main effector (length doesn’t change and viscosity of blood is regulated in narrow range)
Diameter changes have large effect (to the power of 4)
What vessels are the greatest contributors to total peripheral resistance/at the seat of TPR? Why?
Smallest arteries and arterioles have the biggest jump in pressure across vessel class
(arterioles are at the seat of TPR)
What is the resistance in the aorta like? Why?
- Low
- Large diameter, relatively short
What is a drop of pressure indicative of?
Change in resistance across vessel class
What is velocity?
Units?
Rate of blood flow through a vessel
(distance blood/fluid moves in a given time)
cm/s
Use an equation to show how flow of blood is related to velocity
Flow = velocity x A (cross sectional area)
Describe the Velocity and area in capillaries
- Total cross sectional area of capillary beds is vast, much bigger than aorta or any other artery
- Slow velocity - much slower than aorta or any arteries
Describe a benefit of the velocity in capillaries being low
- Allows effective delivery of nutrients, oxygenated blood to tissues and waste removal
- Also if velocity was too high, capillaries wouldn’t withstand due to their structure - quite thin
What happens to velocity as capillaries surge into larger veins and into the vena cava?
Velocity increases again
Where is blood fastest in vessel?
Why?
Centre - least resistance
