CAMOSUN COLLEGE BIOLOGY 144 (2010) LABS

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1 LAB 8: CARDIOVASCULAR PHYSIOLOGY PART 1. HEART SOUNDS AND PULSE DETERMINATIONS Introduction Two distinct sounds can be heard during each cardiac cycle. These sounds are commonly described as lub and dup after which there is a pause. The first sound is associated with closure of the atrioventricular valves and signifies the onset of systole as the ventricular pressure rises above the atrial pressure. The second sound is associated with the closure of the semilunar valves at the end of systole. The sounds are not actually the sounds of the valves closing but rather the sound of the turbulence of blood caused by the closure of the valves. Regions of the thorax as shown in Figure 2 are auscultated (listened to) with a stethoscope. In this exercise you will auscultate heart sounds with an ordinary stethoscope. The term pulse refers to the alternating surges of pressure (expansion and then recoil) in an artery that occur with each contraction and relaxation of the left ventricle. Normally the pulse rate equals the heart rate and the pulse averages 70 to 76 beats per minute in the resting state. The pulse may be felt easily on any superficial artery when the artery is compressed over a bone or firm tissue. Refer to Figure 3 to locate common pulse points. Purpose 1. To auscultate heart sounds using a stethoscope and to relate these heart sounds to the cardiac cycle. 2. To demonstrate the thoracic locations where the first and second heart sounds are most accurately auscultated. 3. To accurately determine a subject s apical and radial pulse. Materials stethoscope, alcohol, absorbent cotton, watch or clock with a second hand 8-1

2 Procedure Clean and disinfect the earpieces of a stethoscope with alcohol-soaked cotton and allow to dry. Place the stethoscope in your ears and check the bell by gently tapping. You should hear an amplified tapping sound. Figure 2 Areas of the thorax where valvular sounds can best be detected. To hear the heart sounds which occur from the turbulence caused by the closure of the AV valves, place the diaphragm of the stethoscope on the sternal side of the left nipple at the fifth intercostal space, and listen carefully. The first sound will be a longer, louder sound than the second sound which is short and sharp. If you wish to differentiate individual valve sounds somewhat more precisely, auscultate the heart sounds over specific thoracic regions as shown in Figure 2 above. Record your apical pulse for 60 seconds to obtain a heart rate in bpms (beats per minute) apical pulse rate Explain what causes the first heart sound second heart sound 8-2

3 Referring to Figure 3, palpate the pulse or pressure points by placing the first two or three fingers of one hand over the common carotid artery. Begin by compressing the artery firmly and then ease up on the pressure slightly. Note the regularity of the pulse and record the pulse rate as follows. Using a watch with a second hand, count the beats in a one minute period. Figure 3. Body sites where pulse is most easily palpated Repeat the procedure using the radial artery Compare the apical pulse rate (the heart rate you recorded using the stethoscope) with the radial and carotid pulse rates. Calculate the mean of the 3 values and record this mean on the board REGION apical carotid radial mean RATE BPM Questions: 1. Do the pulse rates differ? 2. Do these values represent resting heart rate values? Explain 8-3

4 Class data Measures of central tendency and variability The normal range of resting heart rate values is bpm, with a mean of approximately 72 bpm. When a variable such as this is assessed in a large group of individuals, a normal distribution of values (bell-shaped curve) is obtained. Central tendency describes the tendency of data to cluster around certain central values, and may me measured as the mean (sum of all values / sample size) median (value above and below which half the values lie) mode (most frequently occurring value) Variablity is a measure of how dissimilar values are. The range of a data set is the simplest measure of variability. range (lowest to highest value) Arrange the resting heart rate values for the entire class from lowest to highest, making sure you record all of the values (some values will likely appear more than once). After you have recorded the values, complete the exercises outlined in the lab assignment. Resting heart rate values of Biology 144 students (in order from lowest to highest): Questions 1. What is the range of the data? range = Is this similar to the population range of bpm? 2. Calculate the mean resting heart rate for the class mean = Is this greater or less than the reported population mean of 72 bpm? 3. Calculate the median heart rate value median = 4. Calculate the mode of the data set mode = 8-4

5 PART 2. BLOOD PRESSURE DETERMINATION INTRODUCTION Blood pressure is defined as the pressure the blood exerts against the blood vessel walls and it is generally measured in the arteries. The alternating contraction and relaxation of the heart results in a rhythmic flow of blood into the arteries which causes the blood pressure to rise and fall with each beat. Determination of blood pressure includes the measurement of systolic pressure, which is the pressure in the arteries at the peak of ventricular contraction and ejection of blood, and the measurement of diastolic pressure, which is the pressure during ventricular relaxation. Blood pressures are reported in millimeters of mercury (mmhg or the pressure required to support a column of mercury of a certain height). The systolic pressure is reported first and the diastolic second. The reading of 120/80 translates to a systolic pressure of 120 mm Hg and a diastolic pressure of 80 mm Hg. Normal blood pressure varies considerably from one person to another dependent on many factors. In this exercise, you will measure arterial pressures by indirect means and under various conditions. You will investigate and demonstrate factors which affect blood pressure. Purpose To determine a subject s blood pressure with a sphygmomanometer. To relate systolic and diastolic pressures to the events of the cardiac cycle. To define the terms related to blood pressure. Materials stethoscope, sphygmomanometer, alcohol swabs, absorbent cotton Procedure Obtain a stethoscope and clean the earpieces with alcohol swabs. Have the subject sit in a comfortable position with one arm resting on a table which is approximately at heart level Examine the standard sphygmomanometer cuff to determine the area to be placed against the brachial artery and wrap the cuff around the subject s arm just above the elbow. The cuff should fit snugly but should not be tight. Palpate the brachial artery to ensure correct placement. Place the earpieces of the stethoscope in your ears and place the diaphragm over the pulse point in the antecubital fossa. (see picture following page) 8-5

6 Close the valve on the side of the rubber bulb and inflate the cuff to approximately 150 mm Hg. (NOTE: cuff sizes vary; use one appropriate for your subject!) Open the valve slightly and listen for pressure sounds. These sounds are caused by the spurting of blood through the narrowed artery under the cuff into the fully open artery below the cuff. The vibrations are called Korotkoff s sounds. These vibrations may cause slight deflections in the needle on the pressure gauge. The pressure at which these sounds are first detected is the systolic pressure. Note the value on the indicator at which this sound first occurs and report on the data sheet. As the cuff deflates, listen for the total disappearance of all sounds (the needle on the gauge will stop deflecting if it was moving during systole). The point at which no sound can be detected is recorded as the diastolic pressure. Note the value on the gauge when the sound disappears and record this on your data sheet. Now, make a similar recording of blood pressure using the other arm and using the automated sphygmomanometer. Record your data. Compute the pulse pressure for each trial. The pulse pressure is the difference between the systolic and diastolic pressures and reflects the amount of blood forced from the heart during systole. This represents the actual working pressure. 8-6

7 Record your blood pressure determinations below: At rest (manual sphygmomanometer) SUBJECT #1 Systolic Diastolic Pulse pressure At rest (automated sphygmomanometer At rest (manual sphygmomanometer) SUBJECT #2 Systolic Diastolic Pulse pressure At rest (automated sphygmomanometer QUESTIONS: 1. Was each subject s routine BP within the ideal range? 2. If not, suggest some factors that might cause a healthy person s blood pressure to be elevated: 3. Were the results obtained with the automated sphygmomanometer the same as those obtained with the manual sphygmomanometer? 4. What is hypertension? 5. What are 2 causes or contributing factors to hypertension? 8-7

8 PART 2. ELECTROCARDIOGRAM (ECG) EFFECT OF EXERCISE ON HEART RATE AND BLOOD PRESSURE Cardiac muscle produces measurable electrical signals that can be detected at the surface of the body. In this lab we will place electrodes in three locations: one on each ankle and one on the right wrist. This is a standard electrode configuration for a non-clinical setting. On it you will see the standard waves which by convention are labeled P through T. Each component can be analyzed in terms of its duration (in seconds), its amplitude (in millivolts) and its configuration (shape of the waveform). Using your text as a reference, label the ECG tracing below: a. P wave, QRS complex and T wave b. P-Q interval, S-T interval, Q-T interval, QRS interval, P-R segment, S-T segment c. Atrial depolarization, ventricular depolarization and ventricular repolarization 8-8

9 The extent to which each of the components is visible depends on where the electrodes are placed and the condition of the heart. The process begins with a relaxed heart (registering about 0 mv). The first sign of activity is called the P wave and represents the electrical activity associated with the depolarization of the atria. The P wave is a small (0.1 mv) signal of about 0.1 second duration. After the P wave there is a brief period, the P-R segment (0.08 sec), during which the impulse spreads through the AV node and the AV bundle and into the left and right bundle branches. No muscle cells are depolarizing at this time hence no electrical activity is being generated. The P-R segment is followed by the QRS complex. The Q portion represents the moment when the impulse begins to depolarize the interventricular septum. The R and S components represent apical and late ventricular depolarization. The whole QRS component lasts no more than 0.1 seconds but has a large amplitude (variable to 1.3mV). This is followed by the S-T segment (0.12 sec) during which time the ventricles are reaching their maximum contraction but are not generating any electrical activity. Finally comes the T wave which represents the electrical activity associated with ventricular repolarization. The various segments and intervals can be used to diagnose problems with the conduction system of the heart. For example, a longer than normal P-Q interval (>0.18 sec) suggests damage to the AV node. If the QRS interval is prolonged, it may indicate a right or left bundle branch block in which one ventricle is contracting later than the other. Materials: Computer with Biopac software disposable electrodes electrode lead cables (SS2L) Procedure: Select a volunteer from your group. This individual must be suitably dressed to exercise and physically capable of moderately strenuous exercise. Record the subject s blood pressure Prepare the subject as follows: a. rub the skin with an alcohol pad over a small area on the inside of both ankles just above the medial malleolus and over the anterior surface of right forearm just above the wrist joint. b. attach disposable electrodes and coloured cables as described below. white cable to right forearm (on anterior surface of wrist) red cable to left ankle (just above medial malleolus) black cable to right ankle (just above medial malleolus) c. attach the connector of the SS2L electrode to channel 2 8-9

10 2. The computer operator should set up the computer as follows: a. start the BIOPAC program and click on lesson 5 b. type the subject s initials followed immediately by number 1 c. have the subject sit quietly and click the Setup button. The subject must remain still for 15 seconds 3. Record the resting ECG a. when the subject is seated and relaxed, and following the instructions on the computer, click calibrate (calibration takes 10 sec) and then record an ECG for 30 seconds b. when you click done the program will save a copy of your ECG c. have your instructor check your recording before printing (you may enlist their help making the recording look nicer before printing) d. obtain printed copies of the subject s resting ECG (one for each person in your group); print with the paper in the landscape orientation. 4. Record a second ECG on the same subject after 5 minutes of moderately vigorous exercise a. disconnect the cables from the electrodes (leave the electrode pads attached to the skin) and have the subject exercise for 5 minutes (briskly walk up and down the stairs, go for a little jog, skip in place..) b. while the subject is exercising, open the BIOPAC program and choose lesson 5; type in the subject s initials followed by the number 2 c. seat the subject as soon as they have finished exercising and quickly connect the cables to the electrodes as before d. perform the Setup (15 sec) and then measure the ECG as you did before 5. Record the subject s post-exercise blood pressure asap after exercise (Table p 12) 8-10

11 RESULTS and QUESTIONS: 1. What happened to the R-R interval after exercise? 2. Note that the R-R interval consists of the sum of QRS, S-T, T-P and P-R. Which of these become shorter when the heart rate increased? 3. What is the length of the cardiac cycle in your subject: before exercise sec after exercise sec 4. What is the heart rate of your subject: before exercise bpms after exercise bpms 5. Cardiovascular training involves elevating the heart rate into the target heart rate zone (65 85% maximum heart rate) for an extended period of time (> 20 minutes) at least 3 times per week. This generally requires sustained vigorous exercise (stair climbing, swimming, cycling, rowing, running, cross-country skiing, etc.). Estimates of target heart rate can be made by calculating an individual s maximum heart rate. An estimate of maximum heart rate can be obtained as follows: maximum HR = 220 age in years What was the target zone for the exercise subject Did your subject reach their target heart rate zone during exercise? 6. Did the amplitude of the waves in the ECG change following exercise? Comment: 8-11

12 Effect of exercise on Blood pressure Record the subject s blood pressure values in the table below subject BP (at rest) BP (postexercise) % change in systolic value % change in diastolic value 1. calculate % change in the systolic and diastolic values. (BP after exercise BP before exercise) % change = X 100 BP before exercise 2. record the percent change values on the board 3. Calculate the mean % change in diastolic and systolic values for the class: mean change in systolic BP = mean change in diastolic BP = 4. Summarize and explain your observations below: 8-12