LAB 15
HEART FUNCTION AND CONDUCTION
Objective: To learn about blood pressure, its influences and regulators. To review and understand
the cardiac conduction system, the cardiac cycle and heart sounds associated with it. To identify
normal and abnormal wave configurations on an ECG.
A. Pulse
As blood is forced out of the heart from ventricular contraction, it causes a surging movement of blood through the
arteries as the ventricles contract (systole) and then relax (diastole). These waves in blood flow are called pulses.
Pulses are normally felt or palpated at pressure points and are more easily palpated in areas where an artery runs over a
bony prominence.
Use the index and middle finger on one hand to palpate your pulse on the opposite wrist. The radial pulse is palpable
just lateral to the tendons on the ventral side of the wrist. Once you obtain a pulse, count the number of pulses that
occur in 15 seconds and record your pulse below:
_________ pulses  4 = ___________ pulses/min.
Record the pulse of a lab partner using the same method as above. Record the results for each of the circumstances
listed below:
Pulse while lying down ____________ /min
Pulse while sitting _________ /min
Pulse while standing _________ /min
Pulse after hyperventilating for 30 seconds (breathing rapidly and deeply) ____________ /min.
QUESTIONS
1.
What happened to the pulse rate as your partner sat up? When they stood?
2.
What specific receptors were most likely responsible for triggering the change in pulse rate as the body
position changed? Where in the body can you find these receptors?
3.
What happened to the pulse rate after hyperventilation?
4.
What receptors were most likely responsible for the change in pulse that occurred following hyperventilation?
To what do these receptors respond?
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B. Arterial Blood Pressure
Blood pressure is the force exerted on the interior walls of vessels by blood as it surges through them. Pressure exerted
during contraction of the ventricle (systole) is higher than the pressure exerted when the ventricles are relaxed
(diastole).
Measure the blood pressure of your lab partner using a stethoscope and a sphygmomanometer. First, practice listening
for blood pulsing through the brachial artery by placing the stethoscope on a lab partner's brachial artery, which is
located in the antecubital region. Once you are able to hear the blood flow, you may begin taking the blood pressure
reading using the following procedure:
1.
Place the cuff of the sphygmomanometer over your lab partner’s upper arm. Slowly, pump air into it by using
the rubber bulb. When you can no longer hear the blood flow (approx. 150 mm Hg), stop the inflation. You
have compressed the brachial artery to the point that blood is no longer flowing through it.
2.
Gradually, release air from the cuff as you listen to the brachial artery through the stethoscope. When you hear
a sharp, clear sound as the blood flow resumes record the pressure at this time as the systolic pressure.
Systolic pressure _____________ mm Hg
3.
Continue releasing the cuff. The point at which you can no longer hear the blood pulsing through the artery is
the systolic pressure. Record the pressure at the first point the sound disappears.
Diastolic pressure ____________ mm Hg
Written in the conventional method, the blood pressure of your lab partner is ___________________.
QUESTIONS
1.
Is the blood pressure reading you just took a systemic or pulmonary reading?
2.
How does pulmonary blood pressure compare to systemic (higher or lower)?
C. Cardiac Conduction
Study the diagram of the cardiac conduction system on the next page. Label the numbered structures. Learn the
function of each of the structures and answer the following questions.
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1
2
3
4
5
6
QUESTIONS
1.
What are structures #1 and #2 composed of?
2.
What causes depolarization of the cells in structures #1 and #2?
3.
Depolarization of the cells in structure #1 leads to contraction of which heart chambers?
4.
Which valves are open and which are closed during the above process?
5.
When the atrioventricular valves (tricuspid and mitral) close, which heart chambers are contracting?
6.
Which structure is the only electrical connection between the atria and ventricles?
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7.
The AV valves will be held tightly shut due to the impulse reaching structure #_______ , called a _________
_____________________ , which causes contraction of the __________________ muscles.
D. The Cardiac Cycle and ECGs
Use the typical ECG reading below to answer the following questions:
QUESTIONS
1.
What cardiac cycle event is occurring at the P?
2.
What event is occurring during the QRS complex?
3.
What event does the T wave represent?
4.
Why isn’t there a visible wave during atrial repolarization?
5.
What is the normal time duration for one complete cycle?
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6.
What is the quiescent period? Where is this period on the ECG reading above?
7.
A patient who has recently suffered a myocardial infarction shows no P wave on the ECG. What region do you
suspect has been damaged? Why?
Complete the on-line exercises and questions on the computers in the back of the lab (case study of Flo Jackson).
E. Heart Function
1.
Define the following terms:
Stroke volume 
Cardiac output (normal values?) 
Starling’s Law of the Heart 
Tachycardia 
Bradycardia 
2.
3.
What effect will each of the following have on stroke volume?
a.
Increased venous blood return to the heart 
b.
Exercise (increased action of skeletal muscle contraction on veins) 
c.
Blood loss 
d.
Sympathetic innervation 
What effect will each of the following have on heart rate or heart function?
a.
Sympathetic innervation 
b.
Parasympathetic innervation 
c.
Carotid and aortic sinuses (baroreceptors) 
d.
Atrial(Bainbridge) reflex 
e.
Epinephrine 
f.
Thyroxin 
g.
Hypercalcemia 
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h.
Hypocalcemia 
i.
Hyperkalemia (potassium) 
j.
Hypokalemia 
QUESTIONS
1.
What is ventricular fibrillation? Can it be corrected? If so, how?
2.
What is congestive heart failure? What might cause it?
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