Haemodynamics Flashcards
define the following:
*pulse pressure
*mean blood pressure
+state the healthy values for these in adults
mean blood pressure/aka mean arterial pressure (MAP)= is the average arterial pressure throughout one cardiac cycle, systole, and diastole
n.b. MAP is considered to be the perfusion pressure of tissues and organs; if MAP is below 60mmHg u can’t sustain organs
MAP= (2/3 DBP) + (1/3 SBP)
OR
MAP= DBP + 1/3 pulse pressure
SBP/ Systolic BP= pressure during systole {max pressure in arteries}. Normally approx 120mmHg
DBP/Diastolic= pressure during diastole {minimum pressure in arteries}. Normally approx 80mmHg
pulse pressure= difference between SBP & DBP {systolic-diastolic}- directly proportional to SV and inversely proportional to arterial compliance
So if the resting blood pressure is 120/80 mm Hg, the pulse pressure is (120-80)= 40. This is considered a healthy pulse pressure. Generally, a pulse pressure greater than 40 mm Hg is unhealthy.
State the relationship between cardiac output, peripheral resistance and blood pressure (MAP)
MAP(blood pressure aka mean arterial pressure)= TPR (total peripheral resistance) x CO (cardiac output)
MAP= TPR x CO
CO= MAP/TPR
Explain the concept of compliance, and its relationship with pulse pressure, stroke volume
compliance= volume/pressure
Arterial compliance is equal to the change in volume (Delta V) over a given change in pressure (Delta P): C = Delta V/Delta P.
N.b. Compliance is the inversely proportional to elastance/elastic recoil
compliance=1/elastance
explain Poiseuille’s law relating vessel radius + resistance to flow
*need to be familiar with but dont need to commit to memory
- Describe the relationship between systemic vascular resistance (R) and the vessel length (L), the vessel radius (r) and blood viscosity (𝜼)
R = 8𝜼L/πr4 - R - resistance to flow
- r - vessel radius
- L - vessel length
𝜂 - blood viscosity
simply put, as the vessel radius increases the flow increases, however if resistance increases, then flow decreases
explain Laplace’s law relating to vessel radius and pressure
*need to be familiar with but dont need to commit to memory
Laplace’s law - pressure that an elastic vessel can withstand depends on:
* The wall tension
* The wall radius
* The wall thickness of the vessel
Wall stress (𝜎t) = {(Ptm)x r}/h
where
𝜎t = wall tension (mmHg)
Ptm = transmural pressure (mmHg)
r = inner radius (cm)
h = wall thickness (cm)
The smaller the radius of the vessel, the greater the pressure that a given wall strength can withstand
Therefore small diameter arterioles only need thin walls to withstand normal arterial pressures
so:
*smaller vessel radius= increased transmural pressure
* increased wall thickness= increased transmural pressure
*wall tension is proportional to pressure only when r is constant
flow is [] proportional to pressure gradient and [] proportional to resistance
flow is directly proportional to pressure gradient and inversely proportional to resistance
what is the difference between
*laminar blood flow
*turbulent blood flow
laminar blood flow= streamlined/smooth, when blood flows in parallel layers without disruption. Laminar flow is prominently observed at low velocities
turbulent blood flow= random + chaotic. There is mixing of the layers; creates murmurs and bruits {med names for sounds of this turbulent blood}
n.b. turbulent blood flow can be caused by atherosclerosis
Laminar flow is linear flow, mainly found in the middle of the vessel. Turbulent flow is any disruption in the laminar flow. Reynold’s number predicts the chances of flow being turbulent
what is a heart murmur
Heart murmurs {caused by turbulent blood flow}are sounds — such as whooshing or swishing — made by rapid, choppy (turbulent) blood flow through the heart
what causes laminar flow to become turbulent?
-increasing velocity
-narrowing of vessel radius (e.g.atherosclerosis)
-increasing viscosity of blood
n.b.as atherosclerotic plaques develop, they not only alter the nonthrombogenic nature of the endothelium but also disrupt normal laminar blood flow and produce increased turbulence.
what is the relationship between pressure, force and area
pressure= force/area
Describe the korotkoff sounds
Korotkoff sounds = In laminar flow there are no sounds - only come up in turbulent flow
- Phase 1 - sharp tapping - 1st sound hear as cuff pressure released - sound provides SBP
- Phase 2 - swishing/whooshing sounds as blood flows through blood vessels as cuff deflates
- Phase 3 - intense thumping sounds (softer than phase 1) as blood flows through artery but cuff pressure is still inflated to occlude flow during diastole
- Phase 4 - softer, blowing, muffled sound that fades as cuff pressure released - aka 1st diastolic reading
- Phase 5 - silence happens when cuff pressure released enough to allow normal blood flow - aka 2nd diastolic reading
what is the relationship between volume, pressure, compliance and elastance
volume/pressure=compliance
pressure/volume= elastance
compliance is inversely proportional to elastance i.e.
compliance= 1/elastance
If an artery wall weakens, its radius [] so pressure it can withstand []
If an artery wall weakens, its radius increases so pressure it can withstand **decreases **
what is the relationship between the following
*blood viscosity and resistance
*vessel length and resistance
*vessel radius and resistance
- blood viscosity is directly proportional to resistance
*vessel length is directly proportional to resistance
*resistance inversely proportional to the fourth power of the radius of that blood vessel
As the vessel dilates (radius increases), the resistance is divided by the change (in radius) to the fourth power
=Decreasing radius increases the resistance so decreases blood flow
what is vasa vasorum
Vasa vasorum are small blood vessels that comprise a vascular network supplying the walls of large blood vessels, such as elastic arteries (e.g., the aorta) and large veins (e.g., the venae cavae).
Vasa vasorum consist of small arteries (arterioles) which enter the vascular wall either from the abluminal surface (vasa vasorum externa) or from the luminal surfaces (vasa vasorum interna) and then arborize to the outer media.
what is haematocrit
haematocrit= the ratio of the volume of red blood cells to the total volume of blood.
or the percentage of RBCs in the total volume of blood
what are the following blood conditions that increase blood viscosity
*polycythaemia
*sickle cell disease
*macrocytosis
*polycythaemia= when patient has too many RBCs; blood becomes more viscous
*sickle cell disease= sickle shaped RBCs stick together/are inflexible; blood more viscous
*macrocytosis= enlarge RBCs; they make blood more viscous
aorta (and major arteries) [] during systole
aorta (and major arteries) [] during diastole
what happens to the aorta when ppl age?
aorta (and major arteries) distend (strech/relax) during systole
aorta (and major arteries) contract during diastole
n.b. when ppl age the aorta stiffens cuz calcification and decrease of elastin, atherosclerosis= this decreases the compliance of the aorta, so inorder to pump same volume of blood, heart has to work harder which increases blood pressure= increased aortic pulse pressure w advanced arterial disease
how to calculate pulse pressure
pulse pressure= SBP- DBP
SBP= systolic blood pressure
DBP= diastolic blood pressure
A normal young adult at rest has a stroke volume of approximately 80 mL. Arterial compliance is approximately 2 mL/mm Hg, which confirms that normal pulse pressure is approximately 40 mm Hg
