Biology 212: Anatomy and Physiology II
Lab #4: Cardiovascular Physiology
___________________________________________________________________
Overview: Our hearts are amazing machines that pump blood throughout our bodies our entire life.
Just think if your heart beats 72 times a minute for 78 years, you will have a heart that has
beat/contracted approximately 3 billion (3,000,000,000) times. How does the heart work? If it is
injured or damaged at some point, how will your physician determine what is wrong and strategize
ways to fix your heart? Electrocardiograms provide important information about the function of
your heart. In this exercise, you will learn the fundamentals of the electrical activities of the heart and
relate these activities to the mechanical actions of pumping. You will also become familiar with your
peripheral circulation and how it is dependent on a beating heart and patent vessels.
The cardiovascular system encompasses the heart and the blood vessels of the body. As seen last
week in lab, it is responsible for distribution of oxygenated blood to the body and deoxygenated blood
to the lungs. The arterial system is really a pressure reservoir to maintain the pressure gradient
generated by the pumping of the heart during systole. Your pulse is evidence of the pressure
generated during systole.
Exercise 1a: Manual determination of pulse.
Heart rate at rest should fall into the range of 55 to 85 beats/minute. A heart rate over 100 beats per
minute is usually considered to be tachycardia (fast). A heart rate under 60 beats/minute is usually
considered to be bradycardia (slow). If you are exercising, your oxygen demands increase and the
heart rate and cardiac output increases to supply more blood and oxygen to your exercising muscles.
At such times,, an elevated heart rate is normal. If you are an athlete or sleeping, a low heart rate is
normal. Any heart rate above 180 to 200 BPM is never safe (depending on age) even when exercising,
and a pulse as low as 40 BPM is never safe.
Manually determine your pulse rate, and then confirm your pulse rate with a finger pulse transducer.
1.
Using your index and middle fingers, palpate the lateral aspect of your wrist where your
radial artery (thumb side of your wrist) should be. You need to apply light pressure to
actually feel the pulse. According to Dr. Joel Felner, author of “An overview of the cardiovascular
system.” in: Clinical Methods: the history, physical and laboratory Examinations, locate the
carotid pulse in the groove just lateral to the trachea anterior to the sternocleidomastoic
muscle. Assessing the carotid pulse is done using light pressure, one side at a time, since
bilateral carotid compression may produce cerebral ischemia and syncope.
2.
Once you have found the pulse, watch a clock with a second hand and count the number of
beats you feel in a 15 second time frame.
(___________________________________ beats in 15 sec ) x 4 = beats per minute
For the following exercises, we will be using a data acquisition system to collect clinical information
about you and your lab partners. These exercises will be carried out using your lab instructor’s
computer connected to the data acquisition system. The exercises will be run as demonstrations for
groups of 4-6 students. You will receive a hard copy of your group’s information.
1
To confirm the manual pulse calculation from above, you will be using a finger pulse transducer. The
pulse transducer is a plethysmograph that fits over your finger and detects the movement/pulse
wave of blood traveling through small arteries in your finger. This pressure wave is detected and
converted to a voltage change that can be recorded by the system. Note the distribution of arterial
blood flow of the hand. Fingers receive blood through the superficial palmar arch as well as through
the deep palmar arch from both the radial and ulnar arteries.
Exercise 1b: Determination of pulse with a pulse transducer.
1.
Place the nickel-sized pressure pad of the pulse transducer on the tip of the middle finger of
either hand of the volunteer. Use the Velcro strap to make sure it is firmly attached but not
tight enough to cut off circulation. Rest this hand in your lap with the palm up.
2.
Start recording. Remind the volunteer to remain relaxed and as still as possible.
Make sure the volunteer is still facing away from the monitor. Add a comment with
the volunteer’s name. Stop recording after 15 seconds.
3.
Highlight a 5pulse trace, and print the results. Determine the pulse rate (beats/min) on this
tracing, and compare this number to the one you manually measured.
Did your numbers for your pulse agree? Explain your answer.
Exercise 2: Palpation of arterial pulses.
1.
Select a volunteer from your group of 4 and locate the radial artery and ulnar artery in the
wrist and the brachial artery above the elbow. (Usually the ulnar pulse is the hardest to find.)
Place a small “x” on the spots so that you can return to these places later in the exercise.
2.
Connect the finger pulse transducer to the volunteer’s middle finger as before. Start
recording. Collect 10 seconds of “normal” data.
3.
Apply firm pressure with the ball of the thumb over the brachial artery and add a comment
“brachial”. Apply the pressure 10 seconds; then release. Quickly add a comment with
“release”.
4.
Repeat step 3 applying pressure to the radial artery and then the ulnar. Make sure your
comments correspond to each artery respectively. Save your data.
5.
Apply firm pressure over both the radial and ulnar arteries simultaneously. Quickly add a
comment with “radial and ulnar.” Apply the pressure for 10 seconds and release. Add a
comment with “release.”
6.
Stop recording, and save your data. You can highlight the data, and print it off.
Were you able to palpate each artery in your volunteer?
Which of the arteries were easier to palpate? Can you give a reason for this difference?
2
How did compression of the individual arteries affect blood flow
to the fingers? Explain your answer.
All vertebrate hearts are said to be myogenic. (Break the
word apart, and you will understand its meaning. The second
part of the word -- genic -- means origin. The first part of the
word is telling you where the source of the signal to contract
comes from. The root myo- means muscle, and in this case, it
means the heart muscle proper is the source for the signal to
contract.) The heart is the source of the signal to contract; it
does not rely on a signal from the nervous system like a
skeletal muscle does, nor does it rely on endocrine signals for
signal initiation. However, both the nervous system and the
endocrine system (as well as some chemicals) can modify the
rate at which the heart beats.
Cells that make up the myocardium (the primary layer of muscle in the heart that generates the
contraction force to push blood through the system) are called contractile cells. The
autorhythmic/conduction cells (nodal cells) depolarize spontaneously without external stimulation
and create the signal the contractile cells need to function.
Exercise 3: Conduction system of the heart.
Obtain one of the large brown heart models with the conduction system outlined. (You probably
looked at this model last week when locating heart anatomy.)
1.
The pacemaker of the heart is the sinoatrial (SA) node located where the superior vena
cava empties into the upper right atrium. It is a green spot on the upper surface of the right
atrium (number 73).
2.
When the SA node “fires”, its wave of excitation spreads laterally over both atria and also
obliquely to the next structure in the conduction system of the heart: the AV Node. The
atrioventricular (AV) node (number 74) is located on the lower medial floor of the right
atrium/atrioventricular septum.
3.
The SA node stimulates the AV node that in turn spreads the impulse toward the ventricles
through the atrioventricular bundle (i.e., Bundle of His).
4.
The atrioventricular bundle passes into the interventricular septum and branches into
right and left bundle branches.
5.
The bundle branches divide into fine conduction myofibers (i.e., Purkinje fibers) towards
the apex of the heart and distribute the electrical impulses to the individual cardiomyocytes
throughout both ventricles.
Exercise 4: ECG
3
The electrical waves of depolarization and repolarization that spread across the heart can be
detected on the surface of the skin.. These electrical currents are detected by an instrument called an
electrocardiograph. The output, or record, from the machine is a graph called an
electrocardiogram (ECG or EKG). It is a record of the change in the electrical currents (in millivolts)
of the heart detected on the surface of the body as a function of time. (This means the time variable
is plotted on the x axis and the voltage difference (mV) is on the y axis.) An ECG is the electrical
recording from at least two electrodes: a recording electrode and a reference electrode. The
connection between the two electrodes is called a lead. If the depolarization wave (summation of all
cardiac cell potentials) is moving towards the recording electrode, the record will produce a positive
or upward deflection. As the depolarization departs but reaches the second electrode, the signal will
again return to baseline. When the signal is only at the second electrode, the recording will be a
negative wave deflection.
The normal ECG has a series of distinct waves called deflection waves (P wave, QRS complex and T
wave). Each part of the ECG represents a specific electrical event in the ventricle. A segment is a
period of time when no waves occur on an ECG trace (e.g., PR segment, ST segment). An interval
includes both a wave and the baseline period between waves (e.g., PR interval, QRS interval, ST
interval).
The first wave deflection of the ECG is the small P wave and is produced when the atria depolarize.
The wave of depolarization is the electrical signal from the contractile cells to begin to initiate
contraction, but this wave does not indicate that the atria have actually contracted to pump blood
into the ventricle.
The time it takes for the impulses to travel from the SA node and enter the septum is represented by
the PR-segment (typically about 0.16-0.18 sec). The QRS complex consists of 3 deflections. The
first negative ventricular deflection is called the Q-wave, the first positive deflection from the
ventricle is called the R-wave, the first negative deflection after the R-wave is called the S-wave. If
there is no positive R-wave, the negative deflection is called a QS-wave. The QRS complex marks
arrival of the wave of depolarization into the septum and ventricular walls. The large size (i.e., large
voltage change) of this complex reflects the large muscle mass of the ventricles. The QRS complex is
typically about 0.08 seconds in duration.
The T wave is the final noteworthy deflection on the trace. This wave marks the change in voltage
created by ventricular repolarization. The ST
segment corresponds to the time when calcium has
entered the cardiac myocytes and the ventricles are
contracting. The period of ejection is typically about
0.31-0.41 seconds in duration.
You might assume the atria do not go through
repolarization based on the above description, but
that would be the wrong assumption. The atria do
repolarize, but this electrical repolarization event is
obscured (hidden) by the depolarization of the
ventricles and the QRS complex.
Heart block and Fibrillation:
Failure to transmit the action potential down part of
the conduction system is called heart block. In
other words, it is the dissociation of atrial and
ventricular excitation. Heart block is a pathological condition. Heart block usually results from
disease and damage to any of the above elements of the conduction system such that the electrical
4
signal is not allowed to propagate through its normal pathway. Normal healing of any damage causes
cardiac muscle to be replaced by connective tissue, and connective tissue is not autorhythmic and
does not readily conduct action potentials. So the damage can be permanent to the conduction
system. Total heart block is when the signal from the atria to the ventricles is blocked completely—
your SA node is no longer the pacemaker for the ventricles. With total heart block, the heart rate
becomes very slow (20-40 beats per minute - the intrinsic rate of depolarization of the AV node patch
of cells). Fibrillation, by contrast, is anarchy in the heart chambers where contraction is random
and unorganized.If it occurs in the ventricles, no blood would be pumped to the body (i.e., brain)
resulting in unconsciousness. Both conditions, heart block and fibrillation, can be easily detected by
the ECG (electrocardiogram).
If you observe the fibrillation pattern (see below), check to see that your electrodes are all firmly
attached to your volunteer. These data collection systems can and do pick up electrical
interference.
Sample ECG With Fibrillation
Saw Tooth ECG Pattern
Conversion to Normal
Prep: Attach the shielded lead cable to the PowerLab connector.
1.
Connect each electrode lead (white, black, green) to
the electrode gels. Place the electrode gels on the
wrists and ankle of the volunteer: positive lead
(green) on left wrist, negative lead (white) on right
wrist and ground (green) on right ankle. This is the
standard electrode placement for a Lead II ECG.
2.
The Bio Amp for the ECG always displays in the third
channel.
3.
Start recording. Remind the volunteer to remain
relaxed and as still as possible throughout the
duration of the sampling period. Add a comment
with the volunteer’s name. Stop the recording after
15 minutes. Save the data.
4.
Highlight the ECG trace, and print off the results. You
should be able to identify the waves on your trace by
referring to the above diagram.
Exercise 5: Associating arrival of ECG depolarization and finger pulse wave trace.
1.
Connect each electrode lead (white, black, green) to the electrode gels. Place the electrode
gels on the wrists and ankle of the volunteer: positive lead (green) on left wrist, negative
lead (white) on right wrist and ground (green) on right ankle.
2.
Place the nickel-sized pressure pad of the pulse transducer on the tip of the middle finger of
either hand of the volunteer. Use the Velcro strap to make sure it is firmly attached but not
tight enough to cut off circulation. Rest this hand in your lap with the palm up
5
3.
The Bio Amp for the ECG always displays in the third channel, and the Pulse transducer will
be displayed on the first channel.
4.
Start recording. Remind the volunteer to remain relaxed and as still as possible throughout
the duration of the sampling period. Add a comment with the volunteer’s name. Stop the
recording after 15 minutes. Save the data.
5.
Highlight the ECG trace and pulse trace together and print off the results. You should be
able to identify the waves on your trace by referring to the above ECG diagram. Also note
that your pulse trace should be offset from the QRS complex.
Example of a student trace:
The blue line is the pulse trace, while the green line is the ECG.
Using your ECG trace: Identify the wave deflections on your trace. You should also be able to determine
3 separate RR intervals and determine an average heart rate. Also determine the PR intervals and the ST
intervals.
RR interval (sec)
PR interval (sec)
ST interval (sec)
Sample 1
Sample 2
Sample 3
Averages:
6
Note that the X-axis is a time scale and is continuous for both traces. Why does the electrical
depolarization event precede the arrival of the pulse distally at the finger? Think about all of the
cellular events that must occur prior to actual contraction of a heart cell.
Consider a person with a long arm (six foot tall WSU Women’s Basketball player) with the arm of a
five foot tall WSU Gymnast. Would the delay between ECG and pulse wave arrival in the finger for
the tall person be shorter, longer or the same relative to the tall person? Why?
Objectives:
1. Define the following terms:
ECG (EKG)
Autorhythmic
T wave
Diastole
Heart block
Interval/Segments
used in this lab
Systole
P wave
myogenic
Q-R-S complex
Units of measurement pulse pressure
2. List the components of the conduction pathway starting with where the signal
originates and ending where it terminates. (Review these structures on the
brown/red heart models.)
3. Define what ECG stands for, and then describe an ECG.
4. Describe why it is important for both sides of the heart to work in unison.
5. Label all of the waves of the ECG, and know what the heart is doing electrically. In
other words, know what each wave electrically represents in terms of heart function
and how each wave is designated.
6. Be able to determine heart rate from your ECG trace.
7. Be able to determine the duration of the cardiac phases of contraction on an ECG
trace.
8. Be able to determine your heart rate by measuring your VENTRICULAR (R-wave)
pulse rate.
9. Relate finger pulse pressures to the ECG trace. Know which causes the waves in each
of the traces, and note how the traces overlap. Why do the finger pulses lag behind
the R-wave? Why do they sometimes even lag behind the end of the T-wave?
7