Biology 212: Anatomy and Physiology II

Biology 212: Anatomy and Physiology II

Lab #4: Cardiovascular Physiology

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Overview: Our hearts are amazingmachines that pump blood throughout our bodies our entire life. Just think if your heartbeats 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.

To confirm the manual pulse calculationfrom 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 commentwith 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 commentwith “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?

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 anddistribute the electrical impulses to the individual cardiomyocytes throughout both ventricles.

Exercise 4: ECG

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 wavemarks 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 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 thefibrillation 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

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:

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) / Diastole / Systole / myogenic
Autorhythmic / Heartblock / P wave / Q-R-S complex
T wave / Interval/Segments used in this lab / 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?

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