Circulation 3: Part II Systemic Circulation Flashcards
Define pressure, transmural pressure, pressure gradient, and hydrostatic pressure.
pressure = force per unit area (1mmg Hg = 1.36 cm water)
transmural pressure - pressure tending to distend or collapse a vessel
pressure gradient- pressure differential between inflow and outflow
hydrostatic pressure - pressure caused by the height of a fluid column (when standing up gravity causing blood to be pulled down, causes pressure at lower extremities, valves in venous side break that up. generated by gravitational forces)
(hydrostatic means water pressure so we use term generally. hydrostatic pressure in capillaries- really just bp in capillaries)
Define mean arterial pressure and provide an equation.
average pressure existing in the aorta and proximal arterial system during one cardiac cycle.
mean arterial pressure = diastolic pressure and 1/3 pulse pressure (systolic/3)
(bc in diastole more than systole)
What are physiological and physical factors that determine arterial bp?
physiological factors- CO (HR x SV), peripheral resistance
physical factors - arterial blood volume (affects CO) affects arterial compliance…
determines arterial bp
physiological and physical factors that det. bp- other factor- how fast does blood run off to peripheral system -det. by peripheral resistance (arterials) blood pumped in, how fast? how fast going out? in and out. increase CO to put more volume in, reduce outflow by increasing peripheral resistance and that pressurizes the system.
Why do you place the bp cuff at same level as heart?
remove effect of gravitational forces
How does an increase in volume of blood change arterial bp?
makes compliance char. of arterial system decrease bc stretching more components of arterial wall - getting lower compliant system as volume goes up. other way will do it is put more volume in, more venous return, heart pumps more volume into arterial system. interact w arterial compliance and w the heart.
arterial compliance-if low compliant system higher systolic and lower diastolic pressure.
Discuss how the following physiological factors affect systolic and diastolic pressures. What changes them/how are they regulated?
cardiac output peripheral resistance baroreceptor reflex exercise diseas
- cardiac output (stroke volume x heart rate):
a) primarily affects systolic pressure.
b) regulated by autonomic nervous system, can change beat to beat. - peripheral resistance:
a) primarily affects diastolic pressure.
b) regulated by autonomic nervous system, relatively constant.
c) regulated by local metabolic activity – local regulation overrides nervous control.
a) Baroreceptor Reflex – acts via the autonomic nervous system to affect both cardiac output and peripheral resistance.
b) Exercise – systolic pressure increases and diastolic pressure remains constant or decreases (depending on level of exercise). Therefore, pulse pressure widens and mean arterial pressure increases.
c) Disease – congestive heart failure, infarction, bradycardia, sepsis, all decrease blood pressure. Hypertension increases blood pressure (systolic and diastolic forms of hypertension).
What determines systolic pressure?
heart, SV, beats per minute
(if you’re anxious and someone taking your bp it will be elevated v easily by sympathetic nerve activity. regulated by autonomic nervous system- thats why its v difficult to get a consistent reading.)
can change SV easily by little sympathetic surge. bp cuff over sleeve- more difficult for cuff to constrict artery so it artificially raises the pressure bc machine has to generate more pressure to get the stenosis to occur. if you roll up sleeve and its tight that cuts off blood flow which will alter the bp measurement.
Describe how to change peripheral resistance. What does it affect?
peripheral resistance not changed as easily, primarily affects or det. diastolic pressure. how fast does the blood run off. how fast blood pumped in-systolic, how fast blood runs off to capillaries and venous system-diastolic. diastolic also regulated by autonomic NS but not so easily changed, its relatively constant. also regulated by local metabolic activity- local regulation overrides nervous control. ideas is have to get blood flow to specific organ beds and they can regulate their own blood flow locally - does it by vasodilating or vasoconstriction those pre-capillary sphincters or arterioles and that alters diastolic pressure. again, cardiac O and SV and HR det. systolic and peripheral resistance det. diastolic.
If pulse pressure widens is that always bad for heart? Give an example of when it is good/bad.
no not when exercising.. increasing O consumption.. more work for heart but strengthening heart.
widened pulse pressure with low compliant system -thats years and years of continual low compliance. congestive heart failure reduces SV dramatically and reduces systolic pressure..thats the problem w congestive heart failure- have decrease in contractility which reduces SV
What occurs with sepsis?
sepsis- causes massive vasodilation and diastolic pressure drops out…and have real drop in bp. not enough blood in system to perfuse all vascular beds at same moment, if all them open up your bp drops through floor- thats what sepsis does- response to blood bacterial infection
Describe how arterial compliance and blood volume (physical factors) affect systolic/diastolic pressures.
- arterial compliance: affects both systolic and diastolic pressures.
Determined by location in arterial vasculature, age, blood volume, sympathetic tone, pregnancy. - blood volume: affects stroke volume and arterial compliance.
only commonality between 2 variables is they both affect bp. arterial compliance affected by blood volume - if increase blood volume, increase SV, and you also can raise arterial compliance by stretching vessels too much with increased volume
For a given peripheral resistance, as compliance decreases (L to R) what happens to arterial pulse pressure?
pulse pressure widens.
increase in systolic, decrease in diastolic
Graph slide 5
For a given compliance, as peripheral resistance increases (top to bottom) how are systolic and diastolic pressures affected? Which effect is stronger?
both systolic and diastolic pressures increase (diastolic is affected more)
Slide 5
Describe the graph on slide 5.
In a low compliant system, what kind of pulse pressure do you have? What kind of peripheral resistance? What does this indicate about compliance?
In a low compliance system. Describe diastolic/systolic pressures. Describe how afterload, pulse pressure have changed.
When compliance is 14, what kind of peripheral resistance is there as compared to a higher compliance system? How is systolic/diastolic pressures affected?
graph showing effect of peripheral resistance and compliance- not related to e/o both just factors that can affect pulse pressure. look at one at a time.
if you had low compliant system, in a v high compliant system have v small pulse pressure… low peripheral resistance - bc compliance is v high, nice flexible system have small pulse pressure.
then compare to v low compliance, vessels stiff, diastolic pressure and systolic have both changed…
here have large afterload, large pulse pressure now bc of change in compliance at given peripheral resistance
looking at middle one. compliance at 14. low total peripheral resistance compared to high. look at diastolic pressure…at low-about 70 or 80. now, w v high peripheral resistance diastolic pressure about 130. really high. showing 2 diff variables that can affect systolic/diastolic pressure. not directly related to e/o. 2 diff things and how they both affect pressure. look at one column at a time.
Describe local (intrinsic) control of total peripheral resistance.
Factors that affect local control:
local metabolic changes (O2, CO2, metabolites), endothelium-mediated regulation (EDRF, NO, endothelin), myogenic response
local intrinsic contral then affects arteriolar radius which affects total peripheral reisistance
Slide 6
in general local mechanisms can override global mechanisms. 3 mech. of local control- myogenic…muscle mechanism. endothelial mediated regulation.. release tons of diff substances.. nitric oxide.. (v important) local metabolic …all of these are vasodilators released from metabolic tissue (primarily skeletal muscles)
Describe extrinsic control of total peripheral resistance. (Global regulation)
sympathetic activity (increase with general vasoconstriction, decrease with general vasodilation, get vasoconstriction by activation (alpha receptors cause vasoconstriction) withdraw of symp. activity cause passive vasodilation. withdraws stimulation.),
hormonal effects (angiotensin- prod. usually in response to low bp , epi),
baroreceptor reflex (when bp drops out get increase in sympathetic activity, that causes vasoconstriction and raises total peripheral resistance. prevents blood from running off. baroreceptors regulate by stimulating or withdrawing symp.)
extrinsic control contributes to arteriolar radius which affects total peripheral resistance
What is total peripheral resistance? Describe 2 main ways to control total peripheral resistance.
total peripheral resistance- how fast blood from from arterial system to capillaries to veins. det. by arterioles and pre-capillary sphincters. run off of blood. back to r^4… will determine the total peripheral resistance bc its v sensitive to diameter bc of large exponential. main factor is arteriolar radius- thats whats autonomically regulated. blood viscosity also helps det. total peripheral resistance bc its internal resistance but doesn’t change unless pathological conditions (anemia..) affects how fast blood runs through system. main regulatory factor is arteriolar radius -2 ways to regulate…local control mechanisms and extrinsic control mechanisms…
blood viscosity arteriolar radius (intrinsic and extrinsic control)
How does the autonomic system regulate arterial bp? Describe sympathetic stimulation. (heart, veins, arterioles)
can see symp. NS more imp. in regulating bp than parasympathetic. (circulatory system not specifically regulated by parasympathetic)
symp.-affects veins, heart and arteries. activation of this raises bp and withdraw lowers bp. receptors.
contractility increase SV and HR increases CO directly, HR increase strength of contraction as well through positive staircase… need inflow to have pressure. affects arterial system… by vasoconstricting, increasing peripheral resistance (diastolic goes up, raises bp, prevents the run off… heart pumping blood in, vasoconstriction preventing blood from running off as quickly) venous system venoconstricted-shifts venous function curve up and to the right and that shunts more blood to heart through valves, increases preload, SV (as result of L-tension rel) increases CO. when you withdraw symp. HR does come down but activating para. will also bring HR down.
Slide 7 chart.
