lecture 12 - haemodynamics Flashcards
What are the 2 factors that Flow depends on in haemodynamics?
Pressure gradient, resistance
What is the definition of blood flow?
The quantity of blood passing a given point in the circulation in a given period
What is the unit of blood flow?
mL/min
What are the 3 key patterns of blood flow?
Laminar, Turbulent, Bolus
Where is laminar flow typically found in the vasculature?
Arteries, arterioles, venules ,veins
Where is turbulent flow typically found in the vasculature?
Ventricles, sometimes aorta
Where is bolus flow typically found in the vasculature?
Capillaries
What is the profile of lamina flow?
Parabolic profile
What is the stress occuring in lamina flow?
Shear stress
What is the possible effect of high shear stress on blood vessels?
can tear the endothelium
What is the critical value for turbulent flow?
Reynold’s number - Re
What is the equation for Reynold’s number (for turbulence of blood flow)?
Re = (velocity x vessel diameter x blood density)/blood viscosity
What is the effect on the Re in athersclerotic blood vessels?
Increased - therefore there is increased turbulence
What is Poiseuille’s Law used to determine?
resistance
What are the 3 factors that govern resistance, according to Poiseuille’s Law?
Length of tube, liquid viscosity, tube radius
How can be arterioles be changed to have the biggest effect on peripheral resistance, and why?
Change their radius - because resistance is related to radius^4
What is the pressure difference across the circulation?
The difference between arterial and venous blood pressure
Why are large arteries elastic?
The elasticity helps to reduce fluctuations in flow and pressure generated by the intermittent ejection of the stroke volume. Energy is stored in elastic vessels during systole and released in diastole to keep BP more constant.
What is pulse pressure?
The difference between diastolic and systolic blood pressure
What are the 2 factors that determine pulse pressure?
Stroke volume of left ventricle, arterial stiffness/compliance
How does arteriosclerosis (hardened arteries) increase pulse pressure (difference between diastolic and systolic blood pressure)?
Reduced compliance due to reduced elasticity, which increases pulse pressure
What are some examples of pathologies that would cause a reduced pulse pressure?
Congestive heart failure, haemorrhage, aortic stenosis - because of the decreased stroke volume
What is the effect of a full bladder on blood pressure?
Increased BP with a full bladder
how does smoking affect arterial blood pressure?
Increases due to vasoconstriction
What features of veins allow them to act as capacitance vessels/reservoirs for blood?
They are highly distensible to their high compliance at normal operating pressures.
What are some of the determinants of venous pressure?
Sympathetic innervation, blood volume, breathing, skeletal muscle pump
