Download The Heart as a Pump

The Heart as a Pump
Student Version
I. Introduction
The heart is made of two unusual pumps that work in synchrony. Like most pumps they
can deliver varying amounts of fluid depending upon the needs of the system they supply. During
the lab exercise you will explore the two ways that the output of a pump can be increased or
decreased using a simple physical model which faithfully reproduces most of the important
features of cardiac pumping. Later you will apply this understanding to the way the output of the
heart, the cardiac output, is adjusted to meet the changing needs of the body for greater or lesser
amounts of blood flow. In order to fully understand the heart as a pump it is important to study
the structure of the heart - to see that it is indeed two pumps working side-by-side, each supplying
blood to its own circuit. You will examine a sheep heart, focusing on the construction of the
valves and the route the blood takes through the heart. Finally, you will study models of a human
heart to review and clarify what you have learned.
II. Learning Benchmarks
1. Define the following terminology of cardiac pumping in reference to both the heart and the
physical heart-pump model: end diastolic volume (EDV), end systolic volume (ESV), stroke
volume (SV), ejection fraction (EF), heart rate (HR), ejection, filling, systole, diastole,
cardiac output (CO), cycle
2. Intervals and Rates: a) define the terms interval and rate; b) show how rate is inversely related
to the interval; c) be able to calculate either the rate or the interval from the other
3. Predict the CO based on variation of HR, SV, EDV, ESV, EF
4. Describe the two mechanisms by which cardiac output may be increased or decreased
5. Explain how diastolic filling rate may be increased.
6. Predict and calculate how stroke volume (SV) would vary following changes in EDV and/or
ESV
7. Identify the macroscopic features and locations of the key regions of the heart including the
chambers, valves, tributary vessels and vascular supply (major coronary arteries and veins),
stating the way in which their structure is determined by their primary function.
8. Predict the open or closed state of the cardiac valves when the pressures in the heart chambers
and outflow vessels are known.
9. Trace the movement of blood through the various chambers of the heart, identifying the
sequence of important structures and explaining how this particular sequence is necessary for
the efficient pumping of the heart
Copyright 2000 by the American Physiological Society. Permission is granted to reproduce with proper
citation for classroom or workshop use only. For all other purposes, contact the American Physiological
Society Education Office. ([email protected] )
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III. Underlying Concepts - what you should know before you begin the exercise
1. Pumps: What kind of pumps have you observed? Have you observed a nurse of doctor giving a
vaccination with a syringe? What is required to “push” the solution into the tissue?
2. Applying pressure to a fluid produces flow.
3. What is a cycle? What do you know about seasonal or daily cycles?
Pre-Lab Exercise (To be completed before class)
During the lab you will use the apparatus shown in Figure 1-1.
Important functions of the heart are represented by the syringe
which fills with fluid coming from one source (the beaker) and
then dispenses the fluid to another location (the metering
reservoir). This happens because there is a check valve (labeled
“Inflow valve”) between the syringe and the beaker which allows
flow toward the syringe but prevents flow back into the beaker.
A second outflow check valve in the tubing between the syringe
and the metering reservoir allows the water to flow up the tube
but not back into the syringe. If the plunger of the syringe is not
held in place the water pressure in the beaker will cause water to
flow into the syringe body. Pushing on the plunger causes water
to flow out of the syringe, up through the outflow valve, and into
the metering reservoir. When the syringe fills and empties
repeatedly, the water in the beaker is gradually pumped into the
metering reservoir. Each emptying and refilling of the syringe
constitutes one pumping cycle as illustrated in Figure 1-2. In
the figure the plunger is positioned at the 40 ml mark at the beginning of the cycle. It is then
pushed to the 20 ml mark during the emptying phase. Next, when the plunger is no longer being
pushed, water begins flowing into the syringe from the beaker. This starts the filling phase which
ends when the syringe fills to the 40 ml mark again. When the plunger is pushed forward again, a
new pumping cycle begins.
During the lab you will use the apparatus shown in Figure
1-1. Important functions of the heart are represented by the
syringe which fills with fluid coming from one source (the
beaker) and then dispenses the fluid to another location (the
metering reservoir). This happens because there is a check
valve (labeled “Inflow valve”) between the syringe and the
beaker which allows flow toward the syringe but prevents
flow back into the beaker. A second outflow check valve in
the tubing between the syringe and the metering reservoir
allows the water to flow up the tube but not back into the
syringe. If the plunger of the syringe is not held in place the
water pressure in the beaker will cause water to flow into
the syringe body. Pushing on the plunger causes water to
flow out of the syringe, up through the outflow valve, and
into the metering reservoir.
utflow
set
r eservoir
vv
Copyright 2000 by the American Physiological Society. Permission is granted to reproduce with proper
citation for classroom or workshop use only. For all other purposes, contact the American Physiological
Society Education Office. ([email protected] )
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When the syringe fills and empties repeatedly, the water in the beaker is gradually pumped into
the metering reservoir. Each emptying and refilling of the syringe constitutes one pumping cycle
as illustrated in Figure 1-2. In the figure the plunger is positioned at the 40 ml mark at the
beginning of the cycle. It is then pushed to the 20 ml mark during the emptying phase. Next,
when the plunger is no longer being pushed, water begins flowing into the syringe from the
beaker. This starts the filling phase which ends when the syringe fills to the 40 ml mark again.
When the plunger is pushed forward again, a new pumping cycle begins.
From the above description, define a pumping cycle:
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
The volume of fluid in the syringe immediately before the plunger is pushed is called the Filled
Volume (Filled_Vol). In this example Filled_Vol is 40 ml. The volume left in the syringe at the
end of the inward pumping stroke is the Emptied Volume (Emptied_Vol). In Fig. 1.2,
Emptied_Vol is 20 ml.
How would you find the amount pumped in one cycle, the Cycle Volume , Cycle_Vol.?
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
What is Cycle_Vol. in Fig. 1.2? ___________________________________
The fraction of the Filled_Vol that is pumped out in one cycle is called the Ejection Fraction, EF,
and is calculated as follows:
EF = Cycle_Vol / Filled_Vol
What is the EF shown in Fig. 1.2? ___________________________________
The time from the beginning of one pumping cycle to the beginning of the next is called the
Intercycle interval. It is the time for one complete cycle, and its units are seconds/cycle.
If the syringe fills and empties every 5 seconds, what is the inter-cycle interval? _____________
The Pump Rate, PR, is the number of pumping cycles per unit time, thus it is the reciprocal of the
inter-cycle interval. PR is normally expressed as Cycles Per Minute, CPM. It can be converted
from cycles/sec to cycles/min as shown below:
Copyright 2000 by the Americ an Physiological Society. Permission is granted to reproduce with proper
citation for classroom or workshop use only. For all other purposes, contact the American Physiological
Society Education Office. ([email protected] )
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What is PR if the Intercycle interval is 5 seconds?
______________________________________________________________________________
______________________________________________________________________________
The Pump Output, PO, is the total amount of fluid pumped in one minute.
If the average inter-cycle interval for the pumping illustrated in Fig. 1.2 is 10 seconds, what is the
pump output, PO?
_______________________________________________________________
0 20 30 40 50
10 20 30 40 50
Emptied_Vol
= 20ml
Filled_Vol =
= 40ml
40ml
Filled_Vol
10led
50at40begi
30n20
Fi
IV. Laboratory exercise with the syringe pump
A. Exploration
Go to a stairway in the building and run a total of 4 flights of stairs. When you get back to the lab,
pause and note the state of your cardiovascular system. List the changes in the heart’s function
you are aware of?
B. Task Assignments
C. Procedures
The Instrument Operators will operate the syringe-pump as directed by the Timekeeper who can
use a wrist watch or the wall clock to synchronize the pumping cycles specified for each part of
the exercise.
One of the instrument operators should let the syringe fill and empty several times until the large
air bubbles are purged from the syringe and the outflow tubing. The outflow and inflow tubes
should be filled with water after this is done. Note: The syringe will fill on its own because of
the water pressure from the beaker, and the plunger could come out, so one of the operators
needs to hold the plunger until it is time to begin one of the exercises.
Set the syringe on the table top when you are ready to begin. Think about where you want to
have the syringe placed during each part of the experiment. For consistent results this
should always be the same level relative to the reservoir.
Copyright 2000 by the American Physiological Society. Permission is granted to reproduce with proper
citation for classroom or workshop use only. For all other purposes, contact the American Physiological
Society Education Office. ([email protected] )
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Prior to performing each of the exercises below, open the reset valve to empty fluid from the
metering reservoir into the beaker, and then close it again . Pay attention to the level of fluid in
the metering reservoir since it can overflow.
1. Case 1, 10 second Inter-cycle interval:
Now you will begin to explore the relationship between pump rate, Filled_Vol and
Emptied_Vol. The goal of this exercise is to understand how these factors are inter-related and
then how to use your understanding of their relationships to produce the highest possible pump
output. Your lab group is competing with the other lab groups to see who can obtain the greatest
PO.
In each of the three Cases, the Filled_Vol and Emptied_Vol will be determined by the
timing of the Inter-cycle interval. In Case 1, you will use an Inter-cycle interval of 10 seconds.
Allow 50% of the Intercycle interval for filling and 50% of the time for emptying:
How many seconds will be spent filling? _____________
How many seconds for emptying? __________________
How many cycles/min. will be completed? ____________
a. Push the syringe plunger to the 10 ml mark, hold it there and empty the metering reservoir,
closing the valve when it is empty . Orient the syringe in a way that allows you to read the
volumes, because you will need to record the Filled_Vol and Emptied_Vol for each cycle.
b. When the Timekeeper tells you to, start a minute of pumping, allow the syringe to begin filling
until the filling period has elapsed at which time your Timekeeper will tell you to begin
emptying for the predetermined emptying time. Continue pumping for one minute. Note:
Don’t pull on the plunger; it will fill on its own. Record in Table Ia the Filled_Vol and
Emptied_Vol for each pumping cycle during the minute. These volumes will not be the
same for each cycle.
Table Ia
Copyright 2000 by the American Physiological Society. Permission is granted to reproduce with proper
citation for classroom or workshop use only. For all other purposes, contact the American Physiological
Society Education Office. ([email protected] )
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c. Calculate the Cycle_Vol for each pumping cycle and then compute an average for each of the
volumes in Table Ia.
d. What was the PO, for Case 1?
___________________________________________________________________________
___________________________________________________________________________
e. Calculate the Cycle_Vol from PO:
f. How do the calculated Cycle_Vol and the averaged Cycle_Vol from Table Ia compare?
___________________________________________________________________________
___________________________________________________________________________
g. State in your own words, the relationship between filled volume (Filled_Vol), emptied volume
(Emptied_Vol) and the cycle volume (Cycle_Vol).
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
h. Calculate and fill in the values in Table Ib.
E m p t_ Vo l = ?m l
F ill20
d _30
V 40
o l =50? m l 10 20 30 40 50
10
10 20 30 40 20 30 40 50
Empt_Vol=10ml
2. Case 2: 5 second Inter-cycle interval.
Repeat the experiment as in Case 1 above, but this time use a 5 second Inter-cycle
interval still allocating 50% of the time to filling and 50% to emptying
a. Predict what the PO will be at this higher pumping rate? ______________
b. Fill in the parameters to be used:
Filling time: ________
Emptying time: _______
# of cycles in a minute: ____
c. Record the data in Table IIa and then record the summary data in Table IIb.
Copyright 2000 by the American Physiological Society. Permission is granted to reproduce with proper
citation for classroom or workshop use only. For all other purposes, contact the American Physiological
Society Education Office. ([email protected] )
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d. What was the PO, for Case 2? ________
e. Calculate the Cycle_Vol from PO:
f. Calculate and fill in the values in Table IIb.
Copyright 2000 by the American Physiological Society. Permission is granted to reproduce with proper
citation for classroom or workshop use only. For all other purposes, contact the American Physiological
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g. Fill in Table III
h. State in your own words how the shorter Inter-cycle interval (higher CPM) affected:
Filled_Vol:_____________________________________________________________________
Emptied_Vol:___________________________________________________________________
Cycle_Vol: ____________________________________________________________________
PO:___________________________________________________________________________
i. What is the relationship between Inter-cycle interval and Cycle_Vol?
______________________________________________________________________________
______________________________________________________________________________
j. Based on the data in Table III, does increasing pump rate increase pump output? Explain
your conclusion explaining any differences from your prediction in a. before you did the
experiment.
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
3. Case 3: Maximizing pump output
a. Reflecting on your investigations so far, what kind of changes might maximize pump output,
PO, in addition to increasing the rate? So far pumping rate is the only factor you have changed so
think about other ways to alter the pumping cycle, the apparatus or the way you do the
experiment.
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
_____________________________________________________________________________
b. Based on your answer to the previous question, estimate the maximum output of the pump:
______________________________
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citation for classroom or workshop use only. For all other purposes, contact the American Physiological
Society Education Office. ([email protected] )
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c. Use the setup to test your prediction. Note : Be careful not to push too hard on the
syringe; it could break.
d. If there was a difference between the predicted and observed maximum outputs, explain
them.
______________________________________________________________________________
______________________________________________________________________________
e. List in order of importance and explain what seem to be the most important factors determining
the maximum output of the pump?
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
4. Sheep heart examination Now that you understand the heart as a special kind of pump, you
will examine a sheep heart to learn how its design allows it to function as a very efficient dual
pump. Work with a lab partner for this exercise and following the instructions below as you
examine a pre-dissected preserved sheep heart:
a. Examination of pre -dissected heart:
(1) Use cold tap water to rinse excess preservative from the heart. Look for remnants of the
pericardium that surrounded the heart. This fibroserous membrane has already been removed, but
portions of it may still be attached at the bases of the large vessels at the top of the heart. Notice
the deposits of fat on the surface of the heart surrounding the coronary vessels.
(2) Study the external topography of the heart. All vessels of the heart enter and exit from the
superior aspect. The opposite, pointed end, or the apex, is directed inferiorly. Extending
diagonally from right to left on the anterior surface is one of the coronary vessels. It is usually
covered by fat deposits. This vessel is over the region that separates the two ventricles. Determine
the position of each ventricle and the two atria .
(3) Using the blunt probe locate the superior and inferior venae cavae . These vessels are not
always intact, but at least the openings to a heart chamber will be present. While one of you
gently pushes the probe into the superior vena cava the other should open the heart at one of the
incisions already present. The probe will enter one of the heart chambers. Which chamber is it?
__________________________
(4) What direction would the blood be flowing by following the path of the blunt probe?
__________________________
(5) Where would blood be coming from that enters this heart chamber? _____________________
(6) Gently push the probe on to the next heart chamber. What chamber does it enter?
___________________________
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citation for classroom or workshop use only. For all other purposes, contact the American Physiological
Society Education Office. ([email protected] )
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(7) What structure did the probe pass through as it entered this chamber? ___________________
(8) What is the function of the structure it passed through? _______________________________
______________________________________________________________________________
______________________________________________________________________________
(9) What part of the syringe pump does the structure in (7) above correspond to? _____________
(10) Examine the interior of the heart chamber the probe is entering. Identify the papillary
muscles and the chordae tendineae attached to the three flaps (cusps) of the tricuspid valve.
What do you think they do?________________________________________________________
______________________________________________________________________________
(11) Where does the blood go when it leaves this chamber and what vessel(s) does it travel in?
_________________
(12) Pull the probe out and then gently push it through the place where blood exits this heart
chamber. What structure does the blood pass through as it exits this chamber? _______________
(13) Try to figure out how this structure actually works. Look at it from inside the heart and from
outside. What part of the syringe pump does this correspond to? ___________________
(14) Which side of the heart have you been exploring? ____________________
(15) How do you know this is the side of the heart you think it is? What characteristics are you
relying on to make this judgement?__________________________________________________
______________________________________________________________________________
(16) Gauging from the thickness of the walls of the four heart chambers, list the chambers in
order of increasing strength: ____________, ______________, ____________, ______________
(17) Why might the chambers be capable of different levels of force development?
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
(18) What structure did the probe pass through as it entered this chamber? __________________
(19) Explore the other side of the heart, identifying its inflow vessels, chambers and valves. You
should be able to identify the structures on the sheep and/or human heart that correspond to the
parts of the syringe pump used in the first part of this exercise.
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citation for classroom or workshop use only. For all other purposes, contact the American Physiological
Society Education Office. ([email protected] )
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5. Correlation: How does the sheep and/or human heart relate to that of the syringe pump
model?
(1) In order to relate the function of the syringe-pump to those of the sheep and/or human heart,
define and explain each of the following terms. In the lab define these terms for the syringe-pump
(middle column), then, after the lab session, define them for the heart (right column) stating the
correct physiological terms and adapting the syringe pump definition. (Note: refer to the text for
help)
Filled_Vol
Emptied_Vol
Cycle_Vol
Ejection Fraction
(EF)
Inter-Cycle Interval
Pump Rate (PR)
Pump Output (PO)
Copyright 2000 by the American Physiological Society. Permission is granted to reproduce with proper
citation for classroom or workshop use only. For all other purposes, contact the American Physiological
Society Education Office. ([email protected] )
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(2) In the syringe-pump setup: explain what the beaker which supplies fluid to the syringe
represents? _____________________________________________________________________
______________________________________________________________________________
(3) Explain what the tube leading to the metering reservoir represents? _____________________
(4) In what ways does the syringe-pump differ from the hearts you examined?
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
D. Post-lab Self-Assessment
1. A well-trained athlete has a very low resting heart rate of 50 beats per minute. His heart is fit,
however, having a resting stroke volume of 120 ml.
a. What is his resting cardiac output (ml/min)?
b. If he exercises heavily his heart rate may increase to 200 beats per minute. What would
his cardiac output be then?
c. How else could his heart change its pumping to further increase cardiac output?
2. Someone who is in heart failure may have a greatly enlarged heart which holds a large volume
of blood but is unable to pump very much into the aorta. If the end diastolic volume of such a
heart is 200 ml, the ejection fraction is 25%, and the heart rate is 100 BPM, what is the
cardiac output?
3. Convert the following intervals between heart beats into heart rates in beats/min:
a. 5 sec. _______________
b. 7 sec. _______________
c. 12 sec. _______________
d. 15 sec. _______________
4. A student’s body requires a cardiac output of 5600 ml (5.6 L) per minute to support resting
activity. It was determined that this student has a resting heart rate of 70 BPM.
a. What is the student’s stroke volume? Show your calculations.
b. Measurements under these conditions show that end diastolic volume is 150 ml. What is
the ejection fraction? Show your work.
Copyright 2000 by the American Physiological Society. Permission is granted to reproduce with proper
citation for classroom or workshop use only. For all other purposes, contact the American Physiological
Society Education Office. ([email protected] )
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