Lab 5 Human circulatory and respiratory function
I. Auscultation of heart sounds
Auscultation of heart sounds means to listen to and study the sounds arising from the heart as it pumps blood. These are the result of vibrations caused by the opening and closing of the valves in the heart, and by the blood rebounding against the ventricular and blood vessel walls. Sounds may be heard by using a stethoscope, or monitored more accurately using a phonocardiogram.
Experimental procedure
1. Using a stethoscope, listen to the heart of a group member, paying special attention to the four major auscultatory areas on the chest (figure 1).
II. Measurement of blood pressure
The determination of an individual's blood pressure is one of the most useful clinical measurements that can be taken. By "blood pressure" we mean the pressure exerted by the blood against the vessel walls, the arterial blood pressure being the most useful, and hence the most frequently measured, pressure. You should become familiar with the following pressures used in cardiovascular physiology.
The mean blood pressure is a function of two factors - cardiac output (CO) and total peripheral resistance (TPR). Peripheral resistance depends on the calibre (diameter) of the blood vessels and the viscosity of the blood.
Mean BP = Cardiac output (ml/sec) x TPR
Cardiac output (ml/min) = Heart rate/min x Stroke volume (ml)
Thus, the measurement of blood pressure provides us with information on the heart's pumping efficiency and the condition of the systemic blood vessels. In general, we say that the systolic blood pressure indicates the force of contraction of the heart, whereas the diastolic blood pressure indicates the condition of the systemic blood vessels (for instance, an increase in the diastolic blood pressure indicates a decrease in vessel elasticity).
Experimental procedure
Blood pressure may be measured either directly or indirectly. In the direct method, a cannula is inserted into the artery and the direct head-on pressure of the blood is measured with a transducer or mercury manometer. In the indirect method, pressure is applied externally to the artery and the pressure is determined by listening to arterial sounds (using a stethoscope) below the point where the pressure is applied (Figure 2). This is called the ausculatory method, because the detection of the sounds is termed auscultation. An older and less accurate method is the palpatory method, in which one simply palpates, or feels, the pulse as pressure is applied to the artery. In either of these indirect methods, pressure is applied to the artery using an instrument called the sphygmomanometer. It consists of an inflatable rubber bag (cuff), a rubber bulb for introducing air into the cuff, and a mercury or anaeroid manometer for measuring the pressure in the cuff. human blood pressure is most commonly measured in the brachial artery of the upper arm. In addition to being a convenient place for taking measurements, it has the added advantage of being at approximately the same level as the heart, so that the pressures obtained closely approximate the pressures in the aorta leaving the heart. This allows us to correlate blood pressure with heart activity.
Auscultatory Method
In the auscultatory method, the pressure cuff is used as in the palpatory method, and a stethoscope is used to listen to change in sounds in the brachial artery.. Place the bell of the stethoscope below the cuff and over the brachial artery where it branches into the radial and ulnar arteries (Figure 2). Use your fingers, rather than your thumb, to hold the stethoscope over the artery; otherwise you may be measuring the thumb arterial pressure rather than the brachial artery pressure. With no air in the cuff no sounds can be heard. Inflate the cuff so the pressure is above diastolic (80-90 mm Hg), and you will be able to hear the spurting of blood through the partially occluded artery. Increase the cuff pressure to around 160 mm Hg; this pressure should be above systolic pressure so that the artery is completely collapsed and no sounds are heard.
Now, open the valve and begin to slowly lower the pressure in the cuff. As the pressure decreases you will be able to hear four phases of sound changes; these were first reported by Korotkoff in 1905 and are called Korotkoff sounds.
The auscultatory method has been found to be fairly close to the direct method in the pressures recorded; usually the systolic pressure is about 3 to 4 mm Hg lower than that obtained with the direct method.
Blood pressure varies with a person's age, weight, and sex. Below the age of 35, a woman generally has a pressure 10 mm lower than that of a man. However, after 40 to 45 years of age, woman's blood pressure increases faster than does a man's. The old rule of thumb of 100 plus your age is still a a good estimate of what your systolic pressure should be at any given age. After the age of 50, however, the rule is invalid. The increase in blood pressure with age is caused largely by the overall loss of vessel elasticity with age, part of which is due to the increased deposit of cholesterol and other lipids in the blood vessel walls.
Practice taking blood pressure on your partner until you become adept at detecting the systolic and diastolic sounds. You will find this can be quite difficult in some people, especially those whose arteries are located deep in the body tissues.
We will also use an electronic monitor. This works with a microphone in the cuff itself which will listen to the brachial artery sounds, and assign blood pressure values electronically. How do the values obtained with the electronic method compare with those from the manual auscultatory method?
III. Electrocardiogram
Every living cardiac cell undergoes a regular sequence of electrical changes that initiate the contractile activity (systole) and the relaxation (diastole) of the cell. Thus, the contraction of the heart is associated with a compound action potential that is initiated at the sinus node and sweeps over the conduction path of the heart, preceding the mechanical contraction of the cardiac fibers. During this depolarization and repolarization of the myocardium, a potential difference is created between different regions on the surface of the heart. A separation of charge or potential difference is called a dipole. The electrical potential of the dipole is conducted through an electrolyte solution, such as the interstitial fluid and blood plasma, and eventually reaches the surface of the skin. By placing electrodes on the skin surface, we are able to detect and record the electrical activity over the heart surface prior to its contraction. By measuring the potential changes in various directions across the heart, it is possible to detect abnormalities.
The electrocardiogram (ECKK or EKG) is a graphic record of the action potentials of the heart. It is recorded with an electrocardiograph, and the study of this cardiac electrical activity is called electrocardiography.
Lead I. Right arm to left arm.
The right arm is connected to the negative terminal of the electrocardiograph, and the left arm to the positive terminal. When the right arm is negative to the left arm the record shows an upward deflection. Thus, lead I measures the potential difference between the electrodes on the left and right arms, or across the base of the heart. We can use a lead switching box to change recording modes.
Lead II. Right arm to left leg.
The right arm is connected to the negative terminal, and the left leg to the positive terminal. Thus, lead II measures the potential difference between the left leg and the right arm, or along the long axis of the heart from base to apex.
Lead III. Left arm to left leg.
The left arm is connected to the negative terminal, and the left leg to the positive terminal. This combination allows lead III to measure the potential difference between the left leg and left arm, or along the left side of the heart.
The sinoatrial (SA) node initiates the cardiac impulse (epicardium in this area becomes negative first), and this wave of negativity sweeps over the heart. Because the SA node is nearer the right arm, this are becomes negative while the left arm and left leg are still positive, and the deflection of the record is upward in those leads (I and II). The left arm is closer to the SA node, so in lead III the first deflection is also upward as the left arm becomes negative in reference to the left leg.
Components of Normal ECG Complex
The normal ECG is shown in Figure 7 for a single cardiac cycle.
Normal values for the duration, and in some cases voltage, of the different phases of the ECG complex are shown in Table 2.
Experimental Procedure
1. Follow the set-up procedure for Lesson 5 (Page 7). You will probably want to record for at least two minutes in each case.
2. Does the cycle length ever vary (arrhythmia)? Is there a change in the cycle length (heart rate) with inspiration or expiration? Are any of the waves abnormal?
3. Make routine measurements of
4. In the Review Saved Data file for Lesson 7, you should find an ECG-BPM data file called "Kirsty-13 weeks." This data was collected from my daughter when she was 13 weeks old. Repeat routine measurements with this data. Include a comparison in your reports.
A PR interval (adult) greater the 0.2 sec is abnormal and indicates first degree heart block. In second degree heart block, there are P waves that are not followed by QRS waves; this may occur regularly or irregularly. Third degree heart block is a complete AV dissociation in which P waves occur quite regularly but have no relation to R waves.
The normal duration of QRS complex is 0.08 to 0.12 sec. A duration of more than this indicates bundle branch block, or that the beat has arisen in one of the ventricles- a so called ventricular beat or extra systole
Variations in the T wave are quite numerous and require an expert diagnosis. Inversions of the T wave are not abnormal, especially in lead III. Elevation of the ST segment by more than 2mm is associated with acute injury or anoxia
IV. Arterial pulse wave
Lesson 7 (Page 5). The blood pressure within an artery varies during each cardiac cycle. The highest pressure (systolic) occurs when the heart is in its relaxation phase and no blood is flowing through the semilunar valves. The difference between the systolic and diastolic pressures is called the pulse pressure. A recording of these changes is called an arterial pulse wave. A normal pulse wave over the aorta is shown in Figure 3. The dicrotic notch results when the aortic semilunar valves close, causing the blood in the aorta to rebound against the arterial walls to produce a slight elevation in pressure.
The magnitude and contour of the arterial pulse wave are directly related to the stroke volume and inversely related to the compliance (elasticity) of the arterial vessels. As the vessels lose their compliance (as with age or in arteriosclerosis), the stroke volume increases and the height of the pulse wave increases (pulse pressure increases). An examination of the pulse wave can give valuable clues to the functioning of the arteries and heart, as is seen in the abnormal waves pictured in Figure 4.
The velocity of the pulse wave as it travels down the artery is also an important clinical measurement. The arterial pulse wave moves over the large arteries at a rate of 3 to 5 m/sec and over the small arteries at 14 to 15 m/sec. The difference in velocity is related to the compliance of the vessels - the less compliance a vessel has, the faster the pulse wave will move over it (as in the small arteries). Thus, a measurement of the velocity of the pulse wave can also provide useful information about changes in the vessel's elasticity (compliance). The velocity will vary with the age of the individual (table1).
Recording the Peripheral Pulse
In this experiment, you will record the pulse wave from the tip of the finger; a peripheral pulse. It is recorded using a photoelectric pulse transducer, which measures changes in blood volume (plethysmography). A light source in the transducer transilluminates the finger tip, and the photoconductor detects changes in light intensity within the finger caused by pulsatile variations in blood volume.
Experimental Procedures
1. With the subject seated, attach the transducer snugly to the palmar surface of the middle finger. Record the pulse for 20 seconds with the subject's arm resting on the table. Now have the subject raise the transducer above his head (arm extended) for 30 seconds and record the pulse during the last 10 seconds.
Then have the subject lower the transducer (arm hanging at his side) for 30 seconds. Note the characteristics of the pulse wave profile.
V. Respiration and Airflow
Lesson 8 (Setup page 6). Using the same subject as before, follow the lesson plan. Compare the two ways of determining the rate of respiration, the respiration pneomograph transducer (SS5L) and the temperature transducer (SS6L).
Lesson 12. Using the respiration transducer (SS11L) with the disposable mouthpiece/filter, determine the respiratory capacities of the lung. You will need to calibrate the instrument using the 0.6L syringe.
VI. Exercise physiology aerobic test
Lesson 15 . In this section (the last!!!), you will put some of the tests together in an integrated examination of the effects of exercise on circulatory and respiratory physiology. You will measure ECG, respiration and skin temperature.
This is a very big laboratory session that may take you more than one week to get all of the data together. In your write-ups, which should also be considerable in length, consider your measurements of the subject in terms of the healthy individual as well as how these techniques may be used in a medical diagnostic sense.