Download Studying the Effect of Flow Tube Radius on Fluid

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BGYC34
PhysioEx Lab 5
Cardiovascular Dynamics Marking Scheme
Part 1
Complete PhysioEx lab #5. Hand-in all of the pages associated with the lab. Note that
there are 8 activities to be completed. You DO NOT need to hand in the histology review
supplement. (5 marks)
Marking Note: There are 45 questions. Each question is worth 1 mark. Obtain a mark out
of 45 and then convert it to a mark out of 5.
Activity 1: Studying the Effect of Flow Tube Radius on Fluid Flow
1. What happened to fluid flow as the radius of the flow tube was increased?
Blood flow increased as the radius of the flow tube increased.
2. Circle the correct term within the parentheses: Because fluid flow is proportional to the
fourth power of the radius, increases in tube radius cause increases in fluid flow
(decreases cause decreases).
3. Is the relationship between fluid flow and flow tube radius linear or exponential?
Exponential.
4. In this experiment, a simulated motor changes the diameter of the flow tube. Explain
how our blood vessels alter blood flow.
Blood vessels can alter blood flow by either constricting (vasoconstriction) or
dilating (vasodilation). Rings of smooth muscle around vessels either relax or
constrict to cause the vasodilation or vasoconstriction.
Noradrenaline released from sympathetic nerves can cause vasoconstriction by
acting on alpha adrenoceptors. Adrenaline released from the adrenal gland can
cause vasoconstriction or vasodilation by acting on alpha and beta
adrenoceptors, respectively. The relative quantity of alpha and beta receptors, in
any particular organ, will determine whether there is vasoconstriction or
vasodilation.
5. After a heavy meal when we are relatively inactive, we might expect blood vessels in
the skeletal muscles to be somewhat constricted whereas blood vessels in the digestive
organs are probably dilated.
Activity 2: Studying the Effect of Viscocity on Fluid Flow
6. How does fluid flow change as viscosity is modified?
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As viscosity increases, blood flow decreases.
7. Is fluid flow versus viscosity an inverse or direct relationship?
The relationship is an inverse one.
8. How does the effect of viscosity compare with the effect of radius on blood flow?
Increases in radius cause blood flow to increase. Increases in viscosity cause
blood flow to decrease. Changes in radius have a greater effect on blood flow
than do changes in viscosity.
9. Predict the effect of anaemia (e.g., fewer red blood cells than normal) on blood flow.
Anaemia would lead to a reduction in blood viscosity and therefore an increase
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blood flow.
10. What might happen to blood flow if we increased the number of red blood cells?
An increase in the number of red blood cells would lead to an increase in blood
viscosity and therefore a decrease in blood flow.
11. Explain why changing blood viscosity would or would not be a reasonable method
for the body to control blood flow?
Changing blood viscosity is not a reasonable method for the body to control
changes in blood flow. Red blood cells take energy and time to synthesise.
Therefore there would not necessarily be an available supply of red blood cells
(in the spleen) to increase blood viscosity. Furthermore, changes in blood flow
are often required for certain organs but not for others. A change in red cell
numbers would affect blood viscosity, and therefore flow, in all organs to an
equal extent.
Activity 3: Studying the Effect of Flow Tube Length on Fluid Flow
12. How does flow tube length affect fluid flow?
As blood vessel length increases, blood flow decreases in a negative exponential
manner.
13. Explain why altering blood vessel length would or would not be an good method of
controlling blood flow in the body?
Altering blood vessel length is not a good method of controlling blood flow in the
body. Blood vessel length changes during growth but it is not something that is
physiologically regulated in the short term.
Activity 4: Studying the Effect of Pressure on Fluid Flow
14. How does driving pressure affect fluid flow?
An increase in driving pressure increases blood flow.
15. How does this plot differ from the plots of tube radius, viscosity and tube length?
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The relationship between pressure and flow is linear. The relationship between
radius, viscosity and length is exponential.
Activity 5: Studying the Effect of Radius on Pump Activity
16. When the piston is at the bottom of its travel, the volume remaining in the pump is
analogous to the ESV (end systolic volume) of the heart.
17. The amount of fluid ejected into the right beaker by a single pump cycle is analogous
to stroke volume of the heart.
18. The volume of blood in the heart just before systole is called the EDV (end diastolic
volume) and is analogous to the volume of the fluid present in the simulated pump when
it is at the top of its stroke.
19. Try to explain why this graph differs from the radius plot in the Vessel Resistance
experiment. Remember that the flow rate into the pump did not change, whereas the flow
rate out of the pump varied according to your radius manipulation.
In the experiment in Activity 1, you increased vessel radius and observed an
exponential increase in blood flow that was initially quite flat but then increased
exponentially and continued to increase. In the current experiment (Activity 5)
you increase the radius of the vessel leaving the pump on the right hand side and
see an exponential increase in blood flow as vessel radius increases. However, in
this case the flow rate begins to plateau once the vessel radius reaches 4 mm. In
this case, the flow is being limited by the amount of time that the pump is active
(analogous to the time taken for an individual heart beat; systole). Flow cannot
increase indefinitely (like in Activity 1) because there is a limited time for the
blood to flow out of the pump.
20. As the right flow tube radius is increased, fluid flow rate increases. This is analogous
to dilation of blood vessels in the human body.
21. Even though the pump pressure remains constant, the pump rate increases as the
radius of the right flow tube is increased. This happens because the resistance to flow is
decreased.
22. The heart must contract more forcefully to maintain cardiac output if the resistance to
blood flow in the vessels exiting the heart is increased.
23. Increasing the resistance (that is, constricting) the blood vessels entering the heart
would increase the time needed to fill the heart chambers.
24. What do you think would happen to the flow rate and the pump rate if the left flow
tube radius is changed (either increased or decreased)?
Changing the left flow tube radius would lead to changes in the blood supply to
the pump. Decreasing the left flow tube radius would lead to a decrease in the
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blood supply and therefore reduce the flow rate. Increasing the left flow tube
radius would lead to an increase in the blood supply and therefore increase the
flow rate. Note, you can observe this on the simulation by altering the left tube
radius and observing the effects on flow.
Activity 6: Studying the Effect of Stroke Volume on Pump Activity
25. What happened to the pump’s rate as its stroke volume was increased?
As stroke volume increased, the pump (heart) rate decreased in an exponential
fashion. Note that the total flow remained constant. As SV increased, rate
decreased to maintain a constant flow (cardiac output).
26. Using your simulation results as a basis for your answer, explain why an athlete’s
resting heart rate might be lower than that of the average person.
An athlete’s heart is likely to be stronger and more efficient at pumping blood.
Therefore, they would likely have a larger stroke volume than an average person.
Since stroke volume is higher, heart rate can be lower in order to maintain an
appropriate level of cardiac output under resting conditions.
27. Applying the simulation outcomes to the human heart, predict the effect of increasing
the stroke volume on cardiac output (at any given rate).
At any given heart rate, increasing stroke volume would increase cardiac output.
28. Circle the correct term in parentheses: When heart rate is increased, the time of
ventricular filling is decreased which in turn decreases the stroke volume.
29. What do you think might happen to the pressure in the pump during filling if the
valve in the right flow tube becomes leaky? Remember that the pump offers no resistance
to filling.
If the right flow tube becomes leaky, then some of the blood within the tube
would flow back into the right pump during the period when the pump is not
pumping. This would be expected to increase the pressure in the pump as blood is
now flowing into it from both the left and the right tubes.
30. Applying the concept to the human heart, what might occur in the left heart and the
pulmonary blood vessels if the aortic valve became leaky?
If the aortic valve becomes leaky then you would expect an increase in pressure
within the left heart (ventricle) which in turn would lead to an increase in
pressure in the pulmonary blood vessels. This would likely lead to pulmonary
edaema.
31. What might occur if the aortic valve became slightly constricted?
If the aortic valve became constricted then stroke volume would decrease. The
heart would have to work harder to pump blood through a constricted valve. This
could lead to cardiac hypertrophy and also a pressure increase that could lead to
pulmonary edaema.
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Activity 7: Studying Combined Effects
32. How is flow rate affected when the right flow tube radius is kept constant (at 3.0 mm)
and the left flow tube radius is modified (either up or down)?
Changing the left flow tube radius would lead to changes in the blood supply to
the pump. Decreasing the left flow tube radius would lead to a decrease in the
blood supply and therefore reduce the flow rate. Increasing the left flow tube
radius would lead to an increase in the blood supply and therefore increase the
flow rate.
33. How does increasing left flow tube radius affect pump chamber filling time? Does it
affect pump chamber emptying?
Decreasing the left flow tube radius increases pump filling time. Altering the left
flow tube radius does not alter stroke volume. However, the total amount of flow
out of the chamber is reduced because the increase in filling time has decreased
(heart) rate.
34. What happens to flow and pump rate when you keep the end volume constant and
alter the start volume to manipulate stroke volume?
If you manipulate the start volume (EDV) and keep the end systolic volume
constant then flow (cardiac output) remains the same but (heart) rate increases.
Rate increases to compensate for the decrease in stroke volume.
35. How does changing the left beaker pressure affect flow rate? This change would be
similar to changing pulmonary vein pressure.
Increasing left beaker (pulmonary vein) pressure increases flow rate by
increasing (heart) rate. Stroke volume remains the same. In this case there is
more blood flowing into the pump (left heart) because of the increased pulmonary
vein pressure. You might, in a real person, expect stroke volume to increase due
to the Starling Effect.
36. If the left beaker pressure is decreased to 10 mmHg, how is pump filling time
affected?
Decreasing left beaker (pulmonary vein) pressure increases filling time.
37. What happens to the pump rate if the filling time is shortened?
Increasing filling time leads to a decrease in heart rate. Remember that stroke
volume isn’t changing in this simulation because it has been set (i.e., you control
what it is).
38. What happens to fluid flow when the right beaker pressure equals the pump pressure?
There is an increase in fluid flow when right beaker pressure increases; this
doesn’t change when right beaker pressure is increased to the same level as
pump pressure.
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Activity 8: Studying Compensation
39. Now decrease the right flow tube radius to 2.5 mm and run another trial. How does
this flow rate compare with “normal”?
Flow rate decreases.
40. Leave the right flow tube radius at 2.5 mm and try to adjust one or more conditions to
return flow to normal. How were you able to accomplish this?
1. Decreasing right beaker pressure (full compensation)
2. Increasing pump pressure (full compensation)
3. Increasing left beaker (pulmonary) pressure (partial compensation at least
under these simulation conditions)
4. Increase stroke volume (partial compensation at least under these simulation
conditions)
5. Increase left flow tube radius (partial compensation at least under these
simulation conditions)
41. Circle the correct term within the parentheses: Decreasing the right flow tube radius
is similar to a partial blockage of the aortic valve or increased resistance in the arterial
system.
42. Explain how the human heart might compensate for such a condition.
The heart would have to work harder (generate more contractile force) to
overcome a valve blockage or increased resistance to flow.
43. To increase (or decrease) blood flow to a particular body system would it be better to
adjust heart rate or blood vessel diameter?
It would be better to adjust blood vessel diameter as changing heart rate could
affect blood flow to all of the organs in the body.
44. If we decreased overall peripheral resistance in the human body the heart would need
to generate more pressure to deliver an adequate amount of blood flow and arterial
pressure would be most likely lower because a reduction in TPR lowers blood pressure.
The compensatory increase in heart rate or stroke volume may or may not restore blood
pressure to normal.
45. If the diameter of the arteries of the body were partly filled with fatty deposits, the
heart would need to generate more force to maintain blood flow and pressure in the
arterial system would be higher than normal.
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Part 2 (10 marks)
Answer the following questions. Staple the answers to the back of the PhysioEx pages.
1) What is Poiseuille’s Law? How would each of the physiological factors in Poiseuille’s
Law (equation) affect blood flow? (2.5 marks)
R = 8Lη / πr4 (1 mark)
R = resistance
L= vessel length
η =viscosity
r = radius
Increasing blood vessel length would increase resistance and therefore decrease blood
flow. (0.5 marks)
Increasing viscosity would increase resistance and therefore decrease blood flow. (0.5
marks)
Increasing blood vessel radius would decrease resistance and therefore increase blood
flow. (0.5 marks)
2) How might anaemia, polycythaemia, low erythropoietin levels, splenectomy and
infection affect blood flow? (2.5 marks)
It is sufficient if they say how blood flow is affected. They don’t need to say why (I should
have asked this specifically but I didn’t).
Anaemia is a reduction in the number of red blood cells. Anaemia would reduce blood
viscosity, reduce resistance to flow, and therefore lead to an increase in blood flow. (0.5
marks)
Polycythaemia is an increase in the number of red blood cells. This would increase blood
viscosity, increase resistance to blood flow and lead to a decrease in blood flow. (0.5
marks)
Erythropoietin is involved in the production of red blood cells. Low levels would lead to
a reduction in red cell production and therefore a decrease in blood viscosity, a decrease
in resistance to flow and increased blood flow. (0.5 marks)
Splenectomy (removal of the spleen) would hinder the body’s ability to make and store
red blood cells leading to reduced blood viscosity, reduced resistance and an increase in
blood flow. (0.5 marks)
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Infection would lead to an increase in the number of circulating white blood cells which
would increase blood viscosity, increase resistance and decrease blood flow. (0.5 marks)
3) Cardiac output equals heart rate X stroke volume. All things being equal, increasing
either heart rate or stroke volume will increase cardiac output. However, if heart rate
increases too much, cardiac output can actually decrease. Why? How does increased
sympathetic activity prevent this decrease in cardiac output (2.5 marks)
If heart rate increases to much then filling time decreases. (0.5 marks)
If filling time decreases then end diastolic volume decreases which in turn leads to a
decrease in stroke volume. (0.5 marks)
If heart rate becomes to high, the decrease in stroke volume is so great that cardiac
output decreases despite the increase in heart rate. (0.5 marks)
Increased sympathetic activity enhances calcium sequestering in the endoplasmic
reticulum of the cardiac muscle cells. Therefore, it increases the rate at which the heart
relaxes following systole. This allows the heart to spend more time in diastole (despite a
high heart rate) which allows more time for filling. (1 mark)
4) What is aortic valve stenosis? How and why would aortic valve stenosis be expected to
affect stroke volume? (2.5 marks)
Aortic valve stenosis is a condition in which the aortic valve doesn’t open properly. (1
mark)
Aortic valve stenosis would be expected to reduce stroke volume (1 mark).
This is because the diameter of the opening between the left ventricle and the aorta is
reduced when the valve isn’t properly open. (0.5 marks)