Systemic Circulation Flashcards
Arterial pressure is determined by the interactino of what two components?
Changes in arterial pressure can be affected by what types of changes?
- Determine by an interaction between heart and arterial system
- Magnitude & shape of the pressure wave *pulse wave) are affected by changes in
- peripheral circulation
- cardiac function (cardiac output)
What is the the equation for mean arterial pressure?
What are important characteristic of the aortic wall?
How does this help its function?
- Aorta: elastic tissue - lots of elastin
- designed for energy storage; expansion & recoil
- Stiff structure
- Function
- smoothe flow of blood to the systemic circulation
- pulse wave dampening (pressure pulse coming out of the left venricle)
Fill out the indicated labels of the provided image of arterial pulse wave
What is mean arteiral pressure?
What is the equation?
- average profusion pressure across the entire cardiac cycle
- geometric mean (across the entire cycle)
- MAP = DP + 1/3 PP
- when you substract the diastolic from the systolic, you get pulse pressure
Describe the characteristic of arteries & how this impacts their function
- Structure not much different from aorta
- relatively stiff in comparison to the veins & have a higher pressure at the same volume as veins
- as you move away from the heart there is an increasing stiffness
- affects pulse wave velocity
- as the vessels get stiffer as you move away from the aorta, the velocity increaes
- This combined increasing stiffness, vessel branching & narrowing of lumen diameter creates a central-to-peripheral impedance mismatch
- partial reflection of the advancing pressure wave back toward the heart, lands usually during diastole
- Function
- pressure resevoir
- dampen pulse wave
What are the functions of the pressure wave reflection?
What happens when this wave gest distorted?
- Reflected pulse wave arrives back at the aorta during diastole
- augments diastolic pressure
- enhancing coronary circulation perfusion pressure
- limits transmission of high pressure pulsatile energy to peripheral circulation
- limiting potential damage to microcirculation
- decreases pulse pressure
- augments diastolic pressure
- As we age & in cases of vascular disease, you see an increase in arterial stiffness
- increase pulse wave velocity
- reflected wave returns early; during systole
- changes pulse pressure
- clinical implications
- increase (beginning of diastolic dysfunction)
- systolic pressure
- pulse pressure
- afterload
- work of the heart
- decreased
- diastolic pressure
- coronary perfusionp ressure
- All risk factors for myocardial infarction
- increase (beginning of diastolic dysfunction)
- increase pulse wave velocity
What are the clinical implications for arterial stiffness?
What are the risk factors for arterial stiffness?
- Loss of protective function contributes to
- a spectrum of cardiovascular disease
- pathogenesis of microvascular etiology
- Increased pulse pressure
- cardiac remodeling
- Risk factors
- age
- smoking
- hypertension
- diabetes mellitus
- hypercholesteroemia
How do arterioles impact blood circulation?
- Arterioles - resistance vessels
- Determine volume and distribution of blood flow
- regional changes in resistance affect regional blood flow
- Total peripheral resistance
- total of all resistances based on vasomotor tone
- reflected to the heart through the aorta
- arterioles account for a majority of TPR
- Determine volume and distribution of blood flow
What is the general trend for cross sectional area of vessels from the heart to the periphery & back?
- large decrease in cross sectional area as you move to the periphery & then an increase in cross sectional area as you move back to the heart
What are the walls of the small arteries & arterioles composed of?
What is unique about their walls?
Which are the regulator cells?
What substances do the regulators respond to?
- Smaller arteries & arterioles: largely smooth muscle
- high wall thickness/lumen diameter ration
- endothelial cells: regulate vascular smooth muscle - vasomotor tone
- relax: NO, prostacyclin, endothelium-derived hyperpolarizing factors
- contract: thromboxane-A2, endothelin-1, reactive oxygen species, angiotensin-II
What are capillaries & what are their functions?
Capillaries: single layer endothelial cells- exchange vessels
What is the function of veins and how are they different from arteries?
Veins hold blood
they are thin walled, less muscle & relatively more fibrous as compared to arteries
Low wall thickness/lumen diameter ratio & relatively low resistance
They have smooth muscles & are vasoactive, so they exhibit venomotor tone
What is different about pressure in the veins below the heart?
In a closed system, driving pressure is unaffected by gravity
In veins, below the heart, the hydrostatic pressure column has a much biger impact on their function
In veins below the heart, there is a increased transmural pressure (Pi)- the inside pressure is higher when you are standing
initially, this has very little effect on the external pressure (Pe)
What is the function of valves in the venous system?
- series of one-way valves that facilitate blood back to the heart
- unidirectional flow toward the heart
- limit the effect of the hydrostatic effect on the columnsWh
- interrupt the hydrostatic pressure column veins don’t “see” the full hydrostatic column
What is the equation for venous return?
How is it influenced by venomotor tone?
It is modified by what other factors?
- when venomotor ton increases it will increase conductance & push blood back toward the heart
- Pmc = mean capillary pressure
- blood volume will play a big role in determining venous return
- Pra = right atrial pressure (for all intents & purposes is 0)
- Modified by
- skeletal muscle pump
- auxillary pump - respiratory pump
What factors redistribute the blood within the venous system?
What factors drive the muscle pump?
- Redistributing blood volume
- Body position – acute
- when we stand up, iniitally there is a drop in blood pressure so we have sympathetic stimulation & venous contriction to increase the mean capillary presure to push blood back to the heart
- orthostatic hypotension- when the reflex is blunted - acute
- Postural sway and static balance
- when standing, everyone has a natural sway pattern & when they stand still for a longer time, they sway more, which brings on the muscle pump (muscles like soleus contract) and push blood back toward the heart
- Exercise
- Body position – acute
- Muscle pump
- sympathetic stimulation and venous constriction
What problem can occur with increased transmural pressure?
This can have an effect on what other circulatory factors?
increased transmural pressure - increased Pi
Edema
- over time
- fluid exudation
- fluid will leave the veins b/c the high pressure
- fluid accumulates in the tissue
- increases Pe (surround pressure)
- increase in transmural pressure will effect blood volume
- fluid exudation
- effect on venous return and stroke volume
- ultimately blood pressure
- long term – vericose veins
- separation of the valves in the veins b/c prolonged exposure to high internal pressure
- people who stand a lot or who run a lot
- can get back leak & clotting
What is unstressed vascular volume?
How is it related to mean systemic filling pressure & what factors is Pmsf influenced by?
- Unstressed vascular volume
- volume of blood required to “fill” the heart and vessels with transmural pressure of 0
- will distribute in such a way that the transmural pressure is 0 (internal & external pressures are 0)
- when it does this, you come to a mean systemic filling pressure of ~7 mmHg
- presure everywhere is equal at 7 mmHg
- Mean systemic filling pressure (Pmsf)
- depends on total blood volume
- compliance of arteries & veins
How does activation of the heart influence venous & arterial pressure & volume?
- when activate pump it expends energy to increase the pressure, which is then imparted on the blood & pushes blood from high compliance side (venous) over to the arterial side (low-compliant side)
- caridac output goes up
- volume of blood shifts (venous drops & is added to arterial)
- & because the difference in compliance, the artery pressure is maintained high & the venous pressure relative to the unstressed pressure drops a little
What is the distribution of blood at rest?
Which distribution approximates the stressed volume? unstressed volume?
- At any moment (at rest)
- ~64% venous side
- this is how the veins serve as a resevoir & as you change position of being to exercise, it will push blood over to the arterial side
- ~36% arterial side
- ~64% venous side
- Volume in
- veins approximates the unstressed volume
- arteries approximate the stressed volume
Describe the change in pressure as the blood moves through circulation
What is average systemic pressue?
Pulmonary pressure?
- pressures across the circulation
- See pressure in ventricles,
- then see pressure in the aorta (systolice/diastolic)
- big drop in pressure across the arterioles
- into the capillaries where we have a very low pressure
- coming back tot he veins we come back to the right heart with a slight increase in pressure
- as go back through lungs, you again see a drop to very low pressure
- the a large increase as you make your way back to the left heart
- Systemic pressure (120/80 mmHg)
- Pulmonary pressure (30/5 mmHg)
How is velocity of flow related to cross sectional area?
- High velocity at the aorta where there is a small cross sectional area
- Low velocity at the capillaries because a large cross sectional area
- good b/c exchange is primarily diffusion & this would suffer with a high velocity
- Even lower velocity in the lungs as the cross sectional area increases
- velocity = Flow / Cross Sectionl Area
