Flashcards in Principles of Blood Flow Deck (66)
Stages 1-4 of blood flow and types of pressure
1: steady laminar flow in rigid vessels with static driving pressure
2. high Reynold's number flow (turbulence) with dynamic pressure
3. elastic vessel walls with pulsatile pressure
4. microcirculation with diffusion pressure
flow in series VS in parallel and where such things are the case
series: Q1=Q2=Q3... - in organ systems
parallel: Q=Q1+Q2 (if Q1 and Q2 are in parallel) - in general circulation
why the parallel architecture of circulatory system permits redistribution of blood flow
1. rate of blood flow to each tissue is almost always recisely controlled by tissue need
2. cardiac output is controlled mainly by sum of all local tissue flows
3. arterial pressure regulation is generally independent of either local blood flow or cardiac output control
4. blood is redistributed by adjustment of resistances (precapillary sphincters and arterioles) prior to capillary beds
blood to which organs increase/decrease during exercise?
increase: lungs, heart, brain, bone, muscle
decrease: digestive organs, kidneys
how does linear velocity vary with X-sectional area change?
linear velocity varies inversely as X-sectional area increases
v = Q/A
what is the general cardiac output?
time required for a blood cell to travel between 2 points in the system
-t = length/velocity = volume/flow
blood as a fluid (approximations)
steady flow of incompressible fluids in rigid, straight, cylindrical tubes (good except for smaller vessels)
-not always true: flow is laminar with no slippage at wall, and viscosity is constant across diameter of vessel
--in reality, they don't slide past each other (stay in adjascent paths) but NOT so at boundary of vessel
--also, viscosity is highest at the borders
is blood compressible or incompressible?
where does resistance to blood flow come from?
1. walls of the vessel (drag)
2. viscosity of the blood
both are frictional forces
what does mean linear velocity equal in regards to peak velocity?
MLV = 1/2 peak velocity
what is the major physiological variable that determines resistance to blood flow?
radius of blood vessels (mostly arterioles), then viscosity
relationship between temperature and viscosity
temperature is inversely related to viscosity (so colder = more viscous, less blood flow)
-vasoconstriction supplements temperature by reducing blood flow
relationship between pressure drop and radius, viscosity
the larger the radius, the smaller the pressure drop (inverse relationship)
the more viscous, the larger the pressure drop
laminar flow that breaks down when velocity reaches critical point (for Re>3000; between 2000-3000 is transitional period)
-causes significant losses of kinetic energy
measure of intermolecular attractions in liquid
-determines steepness of velocity gradient
Reynolds Number (Re)
Re = disruptive forces/cohesive forces
4 factors that generate pressure
2. compliance of vessels
3. viscous resistance
audible sounds due to vibrations in heart or vessel walls (also called "bruit")
-don't occur under resting conditions
how does gravity affect blood pressure?
adds or subtracts from pressure generated by heart
-exists whether or not the heart is beating
-doesn't affect flow of blood in circuit of distensible vessels b/c gravitational pressure in arteries is exactly counter-balanced by same gravitational pressure at same level in corresponding veins
-does affect distribution of blood throughout system of distensible vessels
conclusions from Bernouli effect
1. as velocity decreases, dynamic pressure becomes smaller fraction of total pressure
2. as vessel radius narrows, dynamic component increases significantly
created by flowing blood on endothelial wall directed along long axis of vessel
-sheer stress on vessel wall is proportional to viscosity and shear rate (rate at which axial velocity changes from wall to lumen)
sheer stress is directly proportional to viscosity and flow rate, and inversely proportional to cube of vessel radius
-measured in units of pressure
anomalous viscosity of blood
increase in viscosity at low flow rate (blood is non-newtonian, so viscosity changes)
-at low flow rates, rouleaux form, creating higher resistance
what does "to yield shear stress" mean?
blood behaves anomalously, meaning at low flow rates they need a threshold force to get moving
what does blood viscosity depend on?
1. fibrinogen (increased clots)
3. vessel radius (at diameters less than 0.3 mm, viscosity decreases)
4. velocity (higher flow = lower viscosity)
5. temperature (colder = higher viscosity)
at tube diameters less than 0.3 mm (arterioles, capillaries, venules) the apparent viscosity of blood decreases
-due to axial streaming (RBC accumulate in rapidly flowing axial lamina)
does plasma/saline viscosity depend on tube diameter?
no, they are independent
tendency of cell-free plasma to be skimmed off at a branch point of microcirculation
-cause altered hematocrit in small vessels