Biology 450 - Animal Physiology Lab Fall 2004

Lab 9 - Human Cardiovascular and Respiratory Function

In this lab, you will examine cardiovascular and respiratory variables under different physiological conditions, such as rest and exercise.

Auscultation of Heart Sounds

Background

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.

Procedure

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).

Measurement of Blood Pressure

Background

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).

Procedures

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.

Palpatory Method

  1. Have the subject seated, with his or her arm resting on a table.  Wrap the pressure cuff snugly around the bare upper arm, making certain that the inflatable bag within the cuff is placed over the inside of the arm where it can exert pressure on the brachial artery.  Wrap the end of the cuff around the arm and tuck it into the last turn, or press the fasteners together to secure the cuff on the arm.  Close the valve on the bulb by turning it clockwise.
  2. With one hand, palpate (feel) the radial pulse in the wrist.  Slowly inflate the cuff by pumping the bulb with the other hand and note the pressure reading when the radial pulse is first lost.  Then increase the pressure to around 20 mm Hg above this point.  Slowly reduce the pressure in the cuff by turning the valve counterclockwise slightly to let air out of the bag.  Note the pressure when the radial pulse first reappears.  This is systolic blood pressure, the highest pressure in the systemic artery.
  3. Let all the air out of the cuff, allow the subject to rest, and then run a second determination.  Do not leave the cuff inflated for more than 2 minutes, because it is uncomfortable and will cause a sustained increase in blood pressure.
  4. The systolic pressure recorded with the palpatory method is usually around 5 mm Hg lower than that obtained using the auscultatory method.  A major disadvantage of the palpatory method is that it cannot be used to measure the diastolic pressure.

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.

  1. Place the bell of the stethoscope below the cuff and over the brachial artery where it branches into the radial and ulnar arteries (Figure 17.2). 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.
  2. 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.
  3. 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, 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.

Postural Effects on Blood Pressure

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.

Exercise Test

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.

  1. Have the subject sit comfortably.
  2. Record the systolic and diastolic blood pressure every 5 minutes until a constant level is obtained.
  3. Have him or her run up and down several flights of stairs, and then return to the sitting position.
  4. Obtain and record the blood pressure immediately, then every minute for 5 minutes.

Cold Pressor Test

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.

  1. Have the subject sit down comfortably or lie supine.
  2. Record the systolic and diastolic blood pressure every 5 minutes until a constant level is obtained.
  3. Immerse the subject's free hand in ice water (approximately 5 °C) to a depth well above the wrist.
  4. After a lapse of 10 to 15 seconds, obtain the blood pressure every 20 seconds for 1 or 2 minutes and record.  If there is insufficient time to obtain both systolic and diastolic pressure, just measure the systolic value.

Respiratory Movements

Background

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.

Procedures

Be sure to answer the worksheet questions accompanying each exercise.

Setup

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.)

Normal Respiratory Pattern

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. 

Hyperventilation

  1. Record normal ventilation for a few cycles.
  2. At a given signal, mark the recording and have the subject breathe as fast and as deeply as possible for 30 seconds.
  3. At the end of this period, obtain a record of the aftereffects of the hyperventilation.  The subject should allow his breathing to be as involuntary as possible during this post-hyperventilation period.

If the subject gets dizzy while hyperventilating, have him stop, but record the respiratory response.

Hyperventilation in a Closed System

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.

Rebreathing

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.

Effect of Exercise

Record respiratory movements after the subject has exercised by running up and down several flights of stairs (as before, only healthy individuals should participate).

Respiratory Volumes

Background

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 airFor 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.

Procedures

Setup

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.

Tidal Volume (TV)

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.

Expiratory Reserve Volume (ERV)

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.

Vital Capacity (VC)

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?

Inspiratory Reserve Volume (IRV) and Inspiratory Capacity (IC)

From the three previous volume measurements you can now calculate the IRV and the IC (see Figure 3).