Principles Of Haemodynamics Flashcards
What is haemodynamics?
Relationship between blood flow, blood pressure and resistance to flow
What are the key factors in haemodynamics (and how does each affect it?)?
- force (cardiac contraction)
- work (isovolumetric contraction/ ejection)
- pressure (difference between aorta and veins)
- compliance (arterial stretch)
- resistance (arterioles)
- flow velocity (slowing down blood flow in capillaries)
What happens in the rest of the body if there is reduced blood flow to the other parts?
The blockage reduces pressure upstream which alters flow to other areas
What is a portal system?
When one bit of blood goes through multiple capillary beds
Examples of a portal vein?
Hepatic portal vein
What does darcy’s law deal with?
Role of pressure energy in flow
What is darcys law?
Flow = difference in pressure/ TPR
What does Bernoulli’s law deal with?
Role of pressure, kinetic and potential energies in flow
What is blood flow?
Volume of blood flowing in a given time (ml/min)
What is perfusion?
Blood flow per given mass of tissue (ml/min/g)
What is the velocity of blood flow?
Blood flow (cm/s) affected by the cross sectional area through which the blood flows
What are the three patterns of blood flow?
Laminar, turbulent and bolus
Where does laminar flow happen?
Most arteries, arterioles, venules and veins
Where does turbulent blood flow happen?
Ventricles (mixing), aorta (peak flow) and atheroma (bruits)
Where does bolus blood flow happen?
Capillaries
What is laminar flow?
- Blood moves in concentric shells
- there is zero velocity at the walls and maximum velocity at the centre
- this speeds up blood flow through narrow vessels
What is turbulent blood flow?
- blood doesnt flow linearly and in smooth layers
- forms whirlpools and vortices due to increased pressure and velocity
- high flow resistance
What is bolus flow?
- RBCs have a larger diameter than the diameter of capillaries so move in single file
- plasma columns are trapped between RBC
- uniform velocity, with little internal friction and very low resistance
What does Reynolds number describe?
What determines change from laminar to turbulent flow
When does turbulence occur?
When Reynolds number exceeds >2000
What is arterial pressure generated by?
Left ventricular contraction
What are your systolic and diastolic pressures?
Systolic = Pressure when ejecting diastolic = pressure when relaxing
What is pulse pressure?
Difference between diastolic and systolic blood pressure
What does pulse pressure tell you about?
Stroke volume and arterial compliance
What does low compliance mean about pulse pressure?
High pulse pressure
What happens in arteries during exercise?
Greater stretch as more blood is ejected
Leads to less compliance and less recoil and the difference between systole and diastole increases (pulse pressure increases)
What is the formula for mean BP?
Diastolic pressure + 1/3 (pulse pressure)
What controls blood pressure (7)?
Age Disease Distance along arterial tree Blood volume Exercise Emotion Wake/sleep
