Principles of haemodynamics Flashcards
What is the definition of haemodynamics?
Haemodynamics- the relationship between blood flow, blood pressure, and the resistance to flow
What are the key factors in haemodynamics
key factors in haemodynamics:
-force (cardiac contraction)
-work (isovolumetric contraction and ejection)
-pressure (difference aorta to veins)
-compliance (arterial stretch)
-resistance (arterioles)
-flow velocity (slowing down blood flow in capillaries
Explain the low pressure reservoir system
In the venous system:
-the majority of blood goes to the systemic veins and venues (64%)
-the least amount of blood goes to the heart and systemic capillaries (7%)
Describe the pressure between vessels
Arteries > Arterioles > Capillaries > Venules > Veins
Define Starling’s law
Starling’s law- this reservoir of venous blood can be used to increase cardiac output
Define Darcy’s law
Darcy’s law- this discusses the role of pressure energy in the flow of blood
What is the equation for flow in Darcy’s law
flow= Pressure difference (P1-P2)/ Resistance to flow (R)
Define Bernoulli’s law
Bernoulli’s law- role of pressure, kinetic energy and potential energies in the flow of blood (not only pressure)
What is the equation for flow in Bernoulli’s law
Flow= Pressure (P) + Kinetic (pV2/2) + Potential (pressure x height x acceleration due to gravity)
What is the definition of blood flow
Blood flow- volume of blood flowing in a given time (ml/min)
what is the definition of perfusion
Perfusion- blood flow per given mass of tissue (ml/min/g)
What is the definition of velocity of blood flow
Velocity of blood flow- blood flow (cm/s) affected by the cross sectional area but velocity changes if there has been a change in cross sectional area
What are the three patterns of blood flow?
3 patterns of blood flow:
1) Laminar
2) Turbulent
3) Bolus
Describe Laminar blood flow
Laminar:
-most arteries, arterioles, venules and veins
-concentric shells
-zero velocity at walls, maximum velocity at centre
-moves RBCs towards centre
Describe turbulent blood flow
Turbulent:
-ventricles, aorta, atheroma
-blood does not flow linearly and smoothly in adjacent layers due to increased pressure and velocity
-high resistance to flow
Describe Bolus blood flow
Bolus:
-occurs in capillaries
-RBCs have larger diameter than capillaries so moves in a single file.
-Plasma columns are trapped between RBCs
-uniform velocity, little internal friction and very low resistance
Which flow description (law) is valid for only the conditions of laminar flow
Poiseuille’s law is valid, at some critical velocity the flow will become turbulent with the formation of eddies and chaotic motion which does not contribute to the flow rate
Describe the relationship between turbulence and Reynolds number
Turbulence occurs when Reynold’s number exceeds a critical value (>2000)
What is the equation for Reynolds number (RE)
Reynolds number (RE)= Density (p) x Velocity (V) x Diameter (D)/ u (viscosity)
Explain arterial blood flow and pressure in relation to the heart
-pressure exerted by blood on vessel walls and is generated by left ventricular contraction.
-arterial pressure falls steadily in systemic circulation with distance from left ventricle
Arterial blood pressure involves which interactions between four key relationships?
Arterial blood pressure involves interactions between four key relationships:
1) Systolic pressure- pressure when ejecting.
2) Diastolic pressure- pressure when relaxing
3) Pulse pressure- difference between diastolic and systolic pressure
4) Mean blood pressure- average blood pressure
Explain what happens during left ventricular systole
During left ventricular systole:
-60-80% of stroke volume if stored in aorta and arteries as these structures expand.
-energy is stored in stretched elastin
Explain what happens during left ventricular diastole
during left ventricular diastole:
-energy is returned to the blood as the walls of the aorta and arteries contract
- this sustains diastolic blood pressure and blood flow when heart is relaxed
