Midterm Review Flashcards
Arteries/arterioles carry blood….
away from the heart
Veins/venules carry blood….
back to the heart
How would you draw a vascular tree diagram?
Begins with thick conduit to feed artery. Progressively smaller vessels from 1A, 2A, 3A, 4A, 5A arterioles and then capillaries.
Explain the composition variations across the vascular bed, such as large and small diameter arteries and arterioles.
Large diameter arteries are elastic. small diameter arteries are muscular.
What is pulsatile blood flow?
because of the intermittent pumping of the heart, blood flow is pulsatile. Therefore there is a constant flow of blood.
What is Ohm’s law used for describing?
blood flow through a vascular segment.
What is Ohm’s Law?
Blood Flow = ∆ Pressure/Resistance
OR
Q = ∆P/R
Why would Ohm’s law need to be rearranged?
to understand interrelationships between different variables
What does Ohm’s law tell us?
to increase blood flow to a muscle, we can either decrease resistance or increase pressure gradient
What is the formula for vascular resistance?
R = ∆P/Q
What is the formula for vascular conductance?
VC = Q/∆P
When do you use R=∆P/Q?
when P is changing more than Q or initial Q is low anyways
When do you use VC = Q/∆P?
when Q is changing more than P or when initial Q is high anyways
What is Poiseuille’s equation used for describing?
Vascular Resistance
What is Poiseuille’s equation?
Can be simplified to R = 1 / r^4
What do the R, L, n and r mean in Poiseuille’s equation?
Resistance, length, viscosity and radius
What is the relationship between Ohm’s law and Poiseuille’s equation? What can you use Poiseuille for in Ohm’s law?
You can use Poiseuille’s law of resistance (R) to determine Resistance (R) in Ohm’s law.
Explain the interrelationship between blood flow, resistance and radius.
Blood flow (Q) DECREASES as resistance to flow (R) INCREASES because vessel radius (r) gets SMALLER.
How does the pressure drop occur in vascular tree?
Vessel radius decreases from aorta to arterioles, BUT total CSA increases from aorta to arterioles due to the branching structure. This means total resistance is decreasing so pressure will fall.
What are the three factors affecting pulsatile flow?
Compliance, viscoelasticity, inertia.
What is compliance?
change in volume for a given change in pressure
What is viscoelasticity?
resistance to stretch-characteristic of a material that exhibits both viscous and elastic properties.
What is inertia?
related to the mass and viscosity of the blood being accelerated by the systolic blood pressure, and the vessel wall that is being pushed out of the way of the moving blood.
Aorta and conduit arteries are highly….
elastic
Vascular compliance is a measure of….
elasticity
Arterial compliance ensures steady and constant flow through the….
capillaries
Describe the differences shown in the video of water pumping through hose only and hose and balloon.
With only a hose (low or no arterial compliance) there is intermittent flow. With hose and balloon (higher arterial compliance) there is continuous flow.
What is the formula for compliance?
Compliance = ∆Volume/∆Pressure
Compliant arteries store a greater blood volume for a given change in….
pressure
Non-compliant arteries store a lesser blood volume for a given change in….
pressure
How does vascular compliance vary throughout the body?
conduit vessels become less compliant as you move from the aorta to the femoral and other peripheral arteries.
What is the role of compliant arteries in systole?
expand to dampen pressure (keep it from increasing to much)
What is the role of compliant arteries during diastole?
recoil to drive pressure (keep pressure from falling to zero)
High compliance means ______ pulse wave velocity
low
True/False: Vascular compliance affects pulse wave velocity and pulse waveform shape.
True
Stiffer vessels will have _____ compliance and ______ pulse wave velocity.
Lower, Higher
What is a reflected pressure wave?
Heart beats and pumps out “pressure wave”. They meet in systole.
How do reflected pressure waves change as you age?
as you get older, they start to come quicker and they don’t meet at the same time as when you were younger.
Reflected pressure waves contributes to the ________ _________ and can increase ________ blood pressure
pressure waveform, systolic
Reflected pressure waves are a form of _____
hypertension
What happens to arterial vascular compliance when you age?
Aging reduces vascular compliance (stiffens vasculature) and affects blood pressure
Do you see pulse waves in older people? Do older individuals have more or less compliant arteries than young people?
You don’t see pulse wave and older people have less compliant arteries than young people.
Being hypertensive _______ vascular stiffening
accelerates
Explain the trend of reflected waves with aging
reflected wave shifts leftwards with aging and pile up on the wave generated by the heart which increases the amplitude of the pressure waveform.
What is the most compliant vessel?
Aorta
Arterial stiffening (aka reduced compliance) with age causes isolated systolic ___________.
Hypertension
Explain systole, arterial stiffness and aging.
stiffer aorta and large arteries do not expand as much with injection of blood. Therefore, systolic blood pressures increases more than in more compliant blood vessels.
Explain diastole, stiffness and aging.
stiffer aorta and large arteries do not recoil as much during diastole therefore blood is not pushed along the vascular tree and diastolic blood pressure falls.
What is the impact of spaceflight on arterial elasticity?
- spaceflight affects physicality due to not as many muscles being used
- post space flight (6 months) average carotid elasticity was equivalent to the healthy 80 year old
- The changes are not permanent however. rehabilitation when returned to earth can bring it back to their normal values.
What is the relationship between physical exercise and arterial compliance?
Inversely affected. In all results, arterial compliance increases with physical exercise.
What are the sex differences in arterial compliance?
In aortic arch compliance, females are at a value of 15 while males are at 11.
What happens to blood flow of exercising limb as workload increases?
increases linearly to contracting muscles as workload increases to support oxygen demands.
How does this linear increase in blood flow occur during workload increase?
Increase cardiac output and vasodilate the arterioles supplying active muscle
What is calculated by the Fick equation?
oxygen consumption
What is the formula of the Fick equation?
Oxygen consumption = Cardiac output x arterial-venous O2 difference
OR
VO2 = Q x (a-v)O2
What is the arterial venous oxygen difference?
difference in arterial and venous oxygen levels. how much oxygen has been taken from that artery.
What is VO2 max a product of?
maximal cardiac output and maximal oxygen extraction by the muscle
What is the main variable that limits maximal oxygen consumption?
cardiac output
Oxygen consumption versus work graph. Can oxygen consumption be increased indefinitely?
Will increase and then plateau. Can only be increased to a certain degree. Endurance athletes will have highest threshold.
What is stroke volume (SV)?
how much blood comes out of the heart with each beat/pump
What are the four main considerations when discussing predictions of VO2 max?
Cardiac output, heart rate, stroke volume and arterial venous oxygen difference
What two factors predict VO2 max?
Cardiac output and stroke volume
Considering the graphs, why do heart rate and arterial venous oxygen difference not predict VO2 max?
HR and AV difference all get to the same level eventually.
Can we experimentally change stroke volume to investigate its impact on maximal oxygen consumption?
In study done with pigs, the pericardium was removed which increase VO2 max. When pericardium is removed, the heart is no longer restrained and can fill with more blood resulting in greater cardiac output.
Did the pig experiment prove that cardiac output or arterial venous oxygen difference was more important when it comes to determining VO2 max?
Cardiac output
Why do we need to redistribute blood flow to other areas during exercise?
since cardiac output is increased, blood flow needs to be redistributed to skeletal muscle from other areas
What areas is blood redistributed from?
Heart, viscera (stomach, spleen), and other organs such as brain.
What is exercise hyperaemia?
blood flow to active skeletal muscle rapidly increasing during exercise
How do we measure blood flow velocity to exercising muscle?
Doppler ultrasound
Regarding Ohm’s law, what can we do to increase blood flow to muscle?
Either decrease resistance or increase pressure gradient
Regarding Poiseuille’s equation, what can we do to decrease resistance?
increase vessel radius, also known as vasodilation.
What is another formula to examine the regulation of blood flow to muscle during exercise?
Q = VC x ∆P
An increase in vascular conductance means….
vasodilation
What is vascular conductance?
the ease at which blood flows through the circulation at a given pressure
What are the two mechanical mechanisms to increase blood flow?
Muscle pump mechanism and myogenic mechanism
What does the muscle pump mechanism do?
increase pressure gradient across capillary bed to drive arterial inflow. This is only related to ∆P not vascular conductance.
What does the myogenic mechanism do?
The purpose of the myogenic mechanism is to maintain steady state of blood flow. Increases vascular conductance, vasodilation.
What is transmural pressure?
Pin – Pout (pressure on inside of vessel minus pressure on outside of vessel)
Explain the metabolic mechanism to increase blood flow
Several metabolites are released from skeletal muscle during contraction that influence vascular smooth muscle cells to improve vasodilation.
What element leads to dilation in both smaller and larger arterioles?
Potassium (K+)
Where is acetylcholine released from, mechanism for increasing blood flow?
Acetylcholine is released from motor neurons innervating skeletal muscle and this influences arterioles to impose vasodilation.
What drug can we use to test for the acetylcholine mechanism?
Atropine
How does atropine test for acetylcholine mechanism?
Atropine is a muscarinic receptor antagonist. Atropine binds to muscarine receptor and blocks other chemicals from interacting. Blocks acetylcholine and stops vasodilation.
Give a piece of experimental evidence for/against the acetylcholine mechanism. Hint: atropine
5 minutes of exercise in contracting the forearm. Control group and atropine group. In atropine group, there was a ~15% reduction in peak exercise blood flow.
Explain the endothelial mechanism to increase blood flow
the friction of red blood cells ‘rubbing’ against endothelial cells initiates cascades leading to vasodilation
Why is the nitric oxide pathways connection to endothelial-mediated vasodilation?
the increase in calcium in the endothelial cell will lead to activation to produce gas which is nitric oxide. This nitric oxide diffuses into vascular smooth muscle cell and causes vasodilation.
What drug can be used to inhibit nitric oxide synthase to prevent endothelial-mediated vasodilation?
L-NMMA
Based on the evidence (and context) presented, under what condition does the endothelial nitric oxide mechanism have the greatest effect?
If you use L-NMMA, blood flow in forearm does go down and has the greatest effect at heavy levels of exercise.
Explain the prostaglandin mechanism for increasing blood flow
In the endothelial cell, prostaglandins are produced. this leads to increased cAMP and decreased calcium which results in vasodilation.
What is flow-mediated dilation?
technique used to assess the ability of the endothelium to produce vasodilation
What does the procedure of flow-mediated dilation look like?
inflation of a blood pressure cuff to supra-systolic levels around part of a limb to temporarily stop blood flow. (~5 minutes).
What happens after cuff deflation of flow-mediated dilation?
blood flow increases greatly which increases sheer stress, causing endothelial-mediated vasodilation.
What is sheer stress?
red blood cells rubbing against endothelial cells
Why do they keep blood pressure cuff on for 5 minutes in flow-mediated dilation?
You need continued levels of sheer stress to initiate vasodilation, it does not happen right away.
When does brachial vasodilation peak following cuff release in flow-mediated dilation?
1.5 minutes
Explain the red blood cell mechanism for increasing blood flow
During exercise, low partial pressure of oxygen at skeletal muscle causes red blood cells to release ATP which exerts vasodilatory effects.
What are the ATP 2PY receptors responsible for?
decrease in calcium resulting in vasodilation.
What does ascending vasodilation mean?
the vasodilation stimulus is at the 5th or 4th order arteriole. Gap junctions between the endothelial cells and smooth muscle cells support ascending vasodilation. therefore, it begins with the smallest arterioles and works its way up to larger vessels
How can we block gap junctions to prevent the process of ascending vasodilation?
Treatment of sucrose
What is the effect of aging on vasodilation and blood flow?
Ageing impaired the blood flow response to acetylcholine infusion. Thus impairs endothelial vasodilatory mechanisms
What is the impact of exercise on endothelial-mediated vasodilation?
Exercise training improves endothelial vasodilatory mechanisms based on blood flow responses to acetylcholine in older adults too.
Do Males or females have a faster drop in forearm blood flow responses?
age related reduction in blood flow response is less in females up until menopause
In terms of exercise, do both older men and women benefit in terms of flow mediated dilation results?
Post menopausal women did not benefit from mild intensity so heavier intensities may be needed for them to see an improvement.
What is neurogenic vasodilation?
sympathetic neurons representing an additional mechanism for vasodilation
Is there any evidence for neurogenic vasodilation?
Only seen in dogs, cats and rats. These neurons are not present in primates or humans.
What are the benefits of neurogenic vasodilation?
Very fast response and flight or fight model
Explain sympathetic vasoconstriction during exercise
the sympathetic nervous system causes vasoconstriction to increase blood pressure and drive blood flow
Why does vasoconstriction need to occur even at modest levels of exercise?
to prevent excessive vasodilation and blood pressure drops
What experiment was done to show importance of sympathetic vasoconstriction?
Sympathetic neurons were cut therefore not as much vasoconstriction. Blood pressure plummeted and they had to stop exercise.
What is the role of sympathetic vasoconstriction of non-exercising vascular beds during exercise?
vasoconstriction of the visceral bed increases to limit flow to inactive organs and increase blood pressure.
What does the sympathetic nervous system do?
Increase heart rate and stroke volume to increase cardiac output. cause vasoconstriction.
What do postganglionic neurons innervate?
the heart
what do preganglionic neurons do?
release chemicals in the spinal cord
What is TPR?
total peripheral resistance
Explain the sympathetic control of what leads to vasoconstriction
NE causes vasoconstriction by binding to alpha 1 and alpha 2 adrenergic receptors. ATP binds to P2X receptor.
What does P2X receptor cause?
vasoconstriction
What does P2Y receptor cause?
vasodilation
Where is the highest density of a1 receptors in the vascular tree?
conduit level
Where is the highest level of a2 receptors in vascular tree?
proximal (1A, 2A, 3A) arteriole level
Where are most NPY Y1 and ATP P2X receptors in the vascular tree?
at tiniest arterioles just before capillaries
How would you draw the neurotransmitter release of NE?
Large bubble is varicosity where neurotransmitters were stored. action potential fire down neutron. tells voltage gated channel to release calcium. calcium triggers release of neurotransmitters. NE diffuses across and binds with specific receptor of muscle cell.
What are the differences in neurotransmitter release during exercise intensity?
Modify release depending on situation. More frequent with increasing intensity. Low NE to high NE. ATP is dominant at low intensity.
What drug can be infused to block a1 receptor pathway?
prazosin
What drug prevents NE from being released?
bretyllum
How can we measure sympathetic activity in humans?
high performance liquid chromatography and microneurography
What does high performance liquid chromatography show?
provides measures of norepinephrine
What does microneurography show?
shows clusters of sympathetic neurons. can hear firing patterns.
