Phys test 7 Flashcards
(52 cards)
Basic principles of circulatory function
- Rate of blood flow to each tissue of the body is almost always precisely controlled in relation to the tissue need (Flow controlled by tissue need)
- Cardiac output is controlled by the sum of all the local tissue flows
- Arterial pressure regulation is generally independent of either local blood flow control or cardiac output control
- foundation of all of the control mechanisms
First principle
- Q to each tissue is controlled by the tissue need
- most designed to respond to decreases in cardiac output
- local control of arterioles/metarterioles/precapillary sphincsters- BP changes constantly
- Central nervous control and Hormone control- when disaster strikes (not day to day)
- metabolic activity in capillary bed increases= increase Q through that tissue
Second principle
- CO controlled by sum of all local tissue flows (venous return)
- if Q through local tissues goes up and venous return goes up= CO goes up
- left and right side of heart, the CO= same
- preload increase= CO increases
- the heart responds immediately to any changes in venous return- automatic response
- CNS not a big role except there is a certain level of Basal level of sympathetic and parasympathetic tone (only when things get out of wack)
Starling’s Law of the heart
-the heart responds immediately to any changes in venous return- automatic response
Third principle
- arterial pressure regulation is generally independent of either local Q to local tissues or CO control
- BP independent of Q and CO
- important because the capillaries are a parallel circuit so therefore the pressure going in and out is equal
- BP regulation is closely regulated by variety of sensor feedback systems and kidneys
If pressure fall quickly, feedback systems will
- increase in cardiac contractility (increase symp tone) (quick change)
- constrict large veins which transfers volume to arteries (quick change)= venous return goes up=CO goes up
- stimulate generalized constriction of arterioles holding more volume in arteries (increase resistance=volume of blood in arteries=BP increases)(quick change)
- stimulate renal controlled change in overall circulating blood volume (slow change)
- controlled by ANS
Hemodynamic principals
- ohm’s law- relationship between blood flow, pressure drop across the system, and resistance to flow through the system (dP=QxR)
- reynolds’ number- measure of the tendency for turbulence to occur
- poiseuille’s law- factors that affect resistance to flow though the system.
flow through vessels in series
P=QR
- Q same through all vessels in series
- pressure drop across each segment depends on resistance of each segment
- velocity of flow will vary inversely with diameter of the vessel- the smaller the diameter the higher velocity
- when velocity drops (such as through the filters), it makes it easier for the air bubbles to leave the blood stream and into purge
flow through vessels in parallel
P=QR
- relationship between total resistance and resistance of each individual tissue=total resistance is always smaller than the smallest resistance within the tissues
- pressure coming in and out must be the same for each vessel
- Total flow through all vessels = flow into the network and flow out of the network
Laminar flow
- silent flow
- center of flow fastest, no flow at boundary layer
Turbulent flow caused by
- high velocity of blood
- narrowing of blood vessel or valve
- mitral stenosis= turbulent flow which causes a murmur sound
- aortic insufficiency= causes a different sounding murmur because of blood flow coming back in
- generates sound Cardiac murmurs
- might be able to feel (bruits) in peripheral blood vessels
Shear Stress (SS)
- force exerted on vessel wall by the moving blood
- force wants to drag the vessels wall along with the blood because the center of the vessel is moving much quicker than the outside and it wants to drag the slower layer with it
- increases resistance to flow and increases hemolysis
- SS = 4(viscosity)Q /(pi)r^3
Reynolds’ number
- measure of tendency for turbulence to occur
- Re = ((velocity)(diameter)(Density)) / (viscosity)
- relationship between forces holding fluid together versus forces trying to pull fluid apart
- ((velocity)(diameter)(Density))= forces pulling fluid apart
- (viscosity)= forces pushing fluid together
Turbulence based on branches
- Side branches turbulence occurs much easier and at a lower Reynolds’ number (R=200-400)
- Straight tube turbulence occurs much higher Reynold’s number (Re= 2000)
- Aorta, when vent ejects you will have turbulence (worse when arterial cannula)
- very seldom in smaller arteries
Poiseuille’s Law
- Q = ((Pi)(ΔP)(r^4)) / ((8)(viscosity)(Length))
- P and Q are same as Ohm’s law and everything else is the R of the law
- diameter has the largest effect
- the larger the diameter, the easier flow and less resistance
- local tissue flow is going to be controlled within the local tissues themselves by changing the diameter of the blood vessels (precapillary sphincters and metarterials)
- SMALL CHANGES PRODUCE BIG CHANGES IN FLOW
what changes viscosity of the blood
- temperature goes down and viscosity goes up
- plasma protein concentration goes down so viscosity goes down
- red blood cell concentration (HCT) goes up so viscosity goes up
- relationship between flow and sheer stress
effects of changing hematocrit of viscosity
- viscosity of plasma= 1.5
- at a normal HCT (40), blood is 3 times more viscous than water (viscosity of 4) and normal body temperature
- plasma protein held constant because viscosity of plasma would have changed
- cool patient= viscosity goes up
- dilute patient= viscosity goes down
effect of flow and shear stress on viscosity
- viscosity is proportional to shear stress
- viscosity inversely proportional to flow
- viscosity increases as sheer stress increases or flow decreases
effect on flow and shear stress on viscosity as a problem
-flow decreases in capillaries because many parallel circuits so flow and diameter will be very small so an increase in viscosity to flow because the resistance is high
capillary sludging
- High resistance in capillary bed because of viscosity so high that the blood becomes less fluid and plug up the capillary so there is no flow= no oxygen able to be sent to that area
- normal in deep hypothermia but metabolic activity is low so won’t need to provide as much
dilute plasma proteins, what happens to viscosity
decreases
dilute RBC, what happens to viscosity
decreases
cool the patient, what happens to viscosity
increases
give a vasoconstrictor, what happens
- decrease diameter of arterioles
- potential to decrease flow through capillaries
- potentially increase viscosity