|Biology 450 - Animal Physiology Lab||Fall 2004|
In this lab, you will examine cardiovascular and respiratory variables under different physiological conditions, such as rest and exercise.
Auscultation of the heart means to listen to and study the various sounds arising from the heart as it pumps blood. These sounds are the result of vibrations produced when the heart valves close and blood rebounds against the ventricular walls or blood vessels. The heart sounds may be heard by placing the ear against the chest or by using a stethoscope. The vibrations producing the sounds can be visually displayed through the use of a heart sound microphone and physiological recorder to produce a phonocardiogram. There are four major heart sounds, but only the first two can be heard without use of special amplification.
Figure 1. The four auscultatory areas.
Using a stethoscope, listen to your partner’s heart sounds, paying special attention to the four major auscultatory areas on the chest where the sounds from each valve can be heard most clearly (Figure 1).
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.
Figure 2. Apparatus for measuring blood pressure indirectly.
The mean blood pressure is a function of two factors – cardiac output (CO) and total peripheral resistance (TPR). Peripheral resistance depends on the caliber (diameter) of the blood vessels and the viscosity of the blood.
Mean BP = Cardiac output (ml/sec) × Total peripheral resistance (TPR units)
Cardiac output (ml/min) = Heart rate/min × 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).
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 auscultatory 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 pressure in the aorta leaving the heart. This allows us to correlate blood pressure with heart activity.
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.
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, a woman's blood pressure increases faster than does a man's. The old rule of thumb of 100 plus your age is still 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.
Measure your partner's blood pressure while she or he is lying down (supine), sitting, and standing. Record your results on your worksheet and also think about what might cause the changes in pressure that accompany these changes in body position.
This test examines the short-term effects of exercise on blood pressure.
Note – The subject should be in good health, with no known cardiovascular or respiratory problems.
This test is used to demonstrate the effect of a sensory stimulus (cold) on blood pressure. A normal reflex response to such a cold stimulus is an increase in blood pressure (both systolic and diastolic). In a normal individual the systolic pressure will rise no more than 10 mm Hg, but in a hypertensive individual the rise may be 30 to 40 mm Hg.
Of the many processes occurring in our bodies each instant, those that function in the movement of oxygen to the tissues are among the most important. If tissues are deprived of oxygen for too long a time, they die; this time factor is especially critical for the cells of vital organs such as the heart and brain. Because of the importance of O2 and CO2, their concentration in the lungs and blood is finely regulated by a variety of receptors, reflexes, and feedback processes that control our respiratory patterns. You can gain insight into some of these control processes by observing a person's respiratory movements and the alteration of these movements caused by various factors.
Also important in oxygen delivery are the capacity of the lungs for air intake and the ability of the lungs to move air in and out quickly. You will analyze these functions when you study the various lung volumes and capacities and conduct the pulmonary function tests.
In our setup, respiratory movements are recorded using a piezoelectric pneumograph (called “Pneumotrace II”) that wraps around the subject’s chest. Piezoelectric devices generate a voltage in response to stretching or bending, which can then be measured directly by our MacLab units. The disadvantage of this type of recorder for a pneumograph is that a constant degree of stretch does not produce a constant voltage – instead, the voltage declines to zero with time. As a result, the Pneumotrace is quite sensitive to rapid changes thoracic (= lung) volume, but not to slower changes. You may have to adjust the sensitivity in Chart to get a useable reading, and the apparent volume of an inhalation or exhalation will be confounded with the speed of volume changes.
In these experiments, the subject should be seated close to the recorder when being tested but should not look at the record. Use a suitable recording rate so that respiratory rates can be determined.
Be sure to answer the worksheet questions accompanying each exercise.
The Pneumotrace is attached directly to one of the input channels on the MacLab unit. Use Chart to record the resulting voltages. (You should be able to handle the details yourself by now.)
Record the subject's normal cyclic pattern of respiration for 1 to 2 minutes using chart. Note the amplitude of the inspiration and expiration cycles.
If the subject gets dizzy while hyperventilating, have him stop, but record the respiratory response.
Repeat the hyperventilation experiment with the subject breathing in and out of a paper or plastic bag. (The bag should be held tightly around the nose and mouth. Be sure to avoid leakage of air from the bag.) Record the respiratory movements after hyperventilation.
Record respiratory movements while the subject breathes in and out of a paper or plastic bag for several minutes. In this case, the subject should allow his breathing to be as involuntary as possible. Observe the rate and amplitude (as well as you can from the Pneumotrace) of ventilation and how these values change over time.
Record respiratory movements after the subject has exercised by running up and down several flights of stairs (as before, only healthy individuals should participate).
The total capacity of the lungs is divided into various volumes and capacities according to the function of these in the intake or exhalation of air. For a proper understanding of respiratory processes, it is necessary that you become familiar with these volumes and capacities.
As shown in Figure 3, the total amount of air one’s lungs can possibly hold can be subdivided into four volumes, defined as follows:
In addition to these four volumes, which do not overlap, there are four capacities, which are combinations of two or more volumes.
Figure 3. Long volumes and capacities for a normal adult male.
The milliliter values given for these volumes and capacities in Figure 3 are for a normal adult male. In the female they are all 20% to 25% smaller.
The respiratory volumes can be measured with a simple instrument called a spirometer. This consists of a lightweight plastic bell inverted in a drum filled with water. A mouthpiece and hose allow the collection of air in the inverted bell. In this experiment you will use your own disposable mouthpiece. Record your results in the table on your worksheet.
The spirometer must be connected to the bridge amp, and then the bridge amp connected to the MacLab. You will also need to calibrate the spirometer in Chart. See if you can do this without instruction.
Set the spirometer dial at zero. Take a normal inspiration, place your mouth over the mouthpiece, and exhale a normal expiration into the spirometer. You will have to make a conscious effort not to exceed your normal volume. Read the amount exhaled on the dial. Have your lab partner count your respiratory cycles for 1 minute while you are seated at rest. Multiply your tidal volume by your respiratory rate per minute to give your resting respiratory minute volume.
Set the spirometer dial at zero. After a normal expiration, place your mouth over the mouthpiece and forcefully exhale as much air as possible into the spirometer.
Set the spirometer dial at zero. Inhale as deeply as possible; place your mouth over the mouthpiece, hold your nose, and exhale into the spirometer with a maximal effort. Repeat the measurement three times and record the largest volume. You can use the nomograms at the end of this handout to determine your predicted vital capacity on the basis of your age, height, and sex. How does your predicted VC compare with your measured VC?
From the three previous volume measurements you can now calculate the IRV and the IC (see Figure 3).