Haemodynamics Flashcards
Define haemodynamics
Movement of blood around the body
What is serum ?
Serum in the blood is the solute and fluid component found after clotting. It is plasma , just without clotting factors.
Changes In viscosity is relatively uncommon for which substance - blood or plasma ?
Whole Blood
How do minor changes in plasma viscosity arise ?
- acute plasma proteins such as fibrinogen , compliment , C-reactive protein (CRP)
- CRP is used to measure plasma viscosity as an indicator of inflammation
What dictates delivery of blood around the body ?
Metabolic demands
blood moves from a high/low pressure to a high/low pressure
High to low pressure
What is laminar flow ?
Laminar flow is movement of blood through vessels through a regulated flow , it is very smoothly driven
- it helps to maintain energy
- typical for most arteries , arteriolar , venules and veins
- with laminar flow , blood flows quicker at the centre of the vessel than at the edges
Turbulent flow
Movement of blood through a vessel in a disorganised flow
- energy is lost through this process
- typically happens during a pathological state
Define flow
Volume transferred per unit time (L/min)
Define pressure
Force per unit area (mmhg)
Define conductance
Measure of ease of low
Identified as K
Define resistance
Measure of difficulty of flow
Identified as R
What is the equation for flow ?
flow = K x ( difference in pressure)
What is the equation for resistance ?
r =-1/k
DARCY’s LAW
FLOW (Q) = Change in pressure /R
What are a few factors that cause
Resistance to flow ? And which one is most important ?
- diameter
- length of vessel
- viscosity
DIAMETER is most important because vessel length doesn’t change and blood viscosity is tightly regulated within a narrow range
Poiseulle’s law
R = 8n(viscosity)x L(length) / pi r^4
- vascular resistance increases with vessel length , blood viscosity but decreases with increased radius.
Flow = change in pressure / R so if resistance decreases due to a 19% decrease in radius , then flow would halve.
In the arteries eg the aorta , is resistance high or low ?
The resistance is low
because R= change in pressure / Flow and there is little change in pressure in the aorta
In the arteriolar and smallest arteries , is resistance high or low ?
- contribute greatest to total peripheral resistance because there is the biggest jump in pressure across vessel class
- arterioles are the seat for peripheral resistance
R= change in pressure / flow
Resistance in the pulmonary circulation is much higher/lower than the systemic circulation ?
Lower in the pulmonary circulation than systemic
-because they have shorter and wider vessels
Define velocity (V)
Distance fluid moves in a given time (cm/s)
How is velocity and flow related ?
FLOW ( F) = V x A
Where A is the cross sectional area of the vessel (pi r^2)
Therefore F ~ V x r^2
At a constant flow V is inversely related to r^2 V~ 1/r^2
Why is velocity at capillary level much slower than at aorta or large arteries ?
Because cross sectional area is vast - thousands times greater than that of aorta or large arteries
V~ 1/r^2
what is pulse pressure
Difference between systolic pressure and diastolic pressure
Measure in mm of mercury (mmhg)
Define Mean arterial pressure
Average blood pressure in an individual during a single cardiac cycle
Mean arterial pressure = CO x total peripheral resistance
What causes an increase in pulse pressure ‘ described as a bounding pulse ‘
- heart block = bradychardia
- vasodilation - decreases peripheral resistance this occurs in the hot bath, pregnancy
- elite athletes : systolic increases and diastolic decreases
Define thrill
When something can be felt
Bruit
When we can hear
What are korotkoff sounds ?
- blood flow sounds that practitioners use observe when taking blood pressure
- these sounds appear and disappear when the cuff is inflated or deflated.
What can be heard and felt over a stenosed vessel ?
If an abnormal sound sound called a bruit is heard , it could reflect turbulent flow of blood which could indicate carotid artery disease
What are the changes in flow and velocity through a stenosed vessel ?
V ~ 1/r^2
- during stenosis ( narrowing of a blood vessel) , the radius ,of the blood vessel decreases which means that the velocity would increase.
- if velocity increases then flow of blood would also increase ( F= VxA)
