Introduction to haemodynamics L1 Flashcards
1
Q
What does haemodynamics mean?
A
- The relationship between blood pressure, blood flow & the resistance to blood flow
2
Q
What is the perfusion pressure?
A
- the difference in pressure between the arteries that supply the region (part of body) and the veins that drain it
3
Q
What does resistance mean?
A
- it is the friction that delays blood flow
- how difficult it is for the blood to flow between 2 points at any given pressure difference
4
Q
What is systolic pressure?
A
- the pressure at the peak of ejection of blood from the heart - highest point
5
Q
What is diastolic pressure?
A
- the pressure during the ventricular relaxation - lowest point
6
Q
What 2 things does vascular resistance depend on?
A
- Vessel geometry - radius & length of vessel (note - radius changes depending on relaxation/contraction & length does not change too much)
- Viscosity of the blood (friction between the molecules of a flowing fluid) - normally stays in a range unless hematocrit changes
7
Q
What is Darcy’s law in CV physiology? What are the main inputs to this equation?
A
- defines blood flow against resistance
- main inputs: Mean Arterial pressure (mm Hg) & total peripheral resistance
- CO =(MAP - CVP/TPR)
8
Q
What is TPR - total peripheral resistance?
A
- the sum of all the vascular resistances within the systemic circulation
- determined by the viscosity of the blood and the total CSA (cross sectional area)
9
Q
What is MAP - mean arterial pressure?
A
- the average arterial pressure throughout one cardiac cycle - systole & diastole
10
Q
What is Poiseuille’s law?
A
- the resistance to flow of liquid through a straight rigid tube is directly proportional to the viscosity of the liquid & the length of the tube
- but is inversely proportional to the 4th power of the radius
11
Q
What does Poiseuille’s law describe?
A
- EG - if there is an decrease in the diameter of the blood vessel and the viscosity of the blood, then there is an increase in the resistance and decrease in the flow rate. However, if there is an increase in the blood vessel diameter, there will be a higher flow rate and thus a lower resistance
12
Q
What is laminar/streamlined flow?
A
- this is the normal state of blood flow in the CV system
- the blood flows in layers/laminae
- the highest point of blood viscosity is in the middle of the vessel
- NB - flow is invers proportional to pressure difference, so if there is an increase in the pressure gradient along the vessel, the flow will eventually become turbulent
13
Q
What is turbulent flow?
A
- turbulent flow is blood flow that does not occur in layers - it is chaotic
- it happens in circumstances in which there is a high flow - eg the aorta/ branch points or a distorted artery due to plaque
14
Q
What is Reynold’s number?
A
- a number that predicts when turbulent flow will occur
- when the Reynolds number is exceeded (Re greater than 2000) , turbulent flow will occur
15
Q
Why is there a fall in pressure from large arteries to veins and capillaries?
A
- As arteries offer greater resistance - they have a thick media layer containing smooth muscle layers and elastic layers and they also have a narrow lumen