Hemodynamics Flashcards
Stressed vs unstressed volume
Arteries contain stressed volume and veins contain unstressed volume.
What contains the most area of blood? The most volume?
Area - capillaries
Volume - veins
Sympathetic activation of veins occurs via
Alpha 1 adrenergic receptors
v =
Q/A
Flow/area
Resistance =
(8nl)/(pi x r^4)
Series resistance
Parallel resistance
Series - sum of individual resistances.
Parallel - sum of the reciprocals.
Laminar flow
Streamlined flow where velocity is greatest at center and least at vessel walls.
Turbulent flow
A disruption of laminar flow and takes more energy to drive turbulent flow forward.
Bruit
When turbulent flow occurs in an artery and may indicate stenosis.
What is the Reynolds number?
Used to predict whether flow will turbulent or laminar.
Less than 2000 indicates laminar flow.
Shear
Changes in the velocity along the vessel. If all areas of the vessel had the same velocity, shear would be zero.
Compliance of vessels
Ability to recoil.
Highest in veins.
Will decrease as patients age.
Pulse pressure
SBP-DBP
Volume of blood ejected from the LV.
MAP =
2/3(DBP) + 1/3(DBP)
Arteriosclerosis causes what effects on SBP, pulse pressure and MAP?
Increases SBP, pulse pressure and MAP.
Aortic stenosis causes what effects on SBP, pulse pressure and MAP?
All will decrease.
Microcirculation
Capillaries.
Occurs via simple diffusion.
Starling equation
Jv = Kf [(Pc-Pi) - (pi.c - pi.i)]
If positive, favors movement from the capillary.
If negative, favors movement into capillary.
Kf
Hydrostatic conductance
What factors favor filtration?
Capillary hydrostatic pressure (Pc)
Capillary interstitial pressure (pi.i)
What factors oppose filtration?
Interstitial hydrostatic pressure (Pi)
Capillary oncotic pressure (pi.c)
How can Kf be increased?
Burns, inflammation.
Autoregulation
Maintaining constant blood flow during changes in pressure.
Active hyperemia
Blood flow to an organ is proportional to its metabolic activity.
Reactive hyperemia
Increased blood flow as a result of a period of decreased blood flow.
Myogenic hypothesis
If smooth muscle is stretched, it will contract, and there will be an increase in arterial pressure.
Tries to explain autoregulation.
Metabolic hypothesis
O2 delivery is matched to O2 consumption.
So if O2 consumption is high, metabolites will be released to cause vasodilation.
JVD
Reflects the activity of the right heart.
Gives an indication of CVP and RAP.
Internal jugular is better to use than external jugular.
What is the most common cause of JVD?
Elevated RV diastolic pressure.
How to measure JVD?
Place patient in supine position and allow veins to engorge. Then raise to 30-45 degrees.
Normally will be between 0-9.
Hepato Jugular Reflex
Distension of veins when pressure is placed over the liver.
Could indicate RV pathology, pericarditis.
Edema grading
0 - 0 mm 1 - 2 mm (nonpitting) 2 - 4 mm 3 - 6 mm 4 - 8 mm
