Section 9
PHYSIOLOGICAL EFFECTS OF SMALL DOSES OF CAFFEINE ON HUMAN SUBJECTS
IMPORTANT NOTEs: The class will serve as the subject pool for this investigation.
Please do not consume any caffeine on the day we collect data for this lab.
Please do not wear hosiery or tights to lab since ECG leads must contact
bare skin.
BACKGROUND
Many people claim that they cannot start their day or stay awake driving
long distances without the caffeine in a cup of coffee. Although large doses
of caffeine can affect many aspects of physiology such as nerve, muscle,
gastric, and kidney function, how much does the small dose of caffeine found
in a single cup of strong coffee influence a person's physiology? Do the
caffeine "buzzes" people report actually result from measurable
effects of the coffee on their physiology, or do they represent a placebo
effect? A placebo effect is a change in an individual's physiology induced
by that person's expectation of the change.
Your job is to:
1. Design an experiment that allows you to investigate the effect of the
dose of caffeine found in a single cup of strong coffee on the physiological
variable of your choice.
2. Control for the possible existence of a placebo effect.
You will have the following materials at your disposal:
Instant coffee - caffeinated and decaffeinated (water decaffeination process)
same brand for both types of coffee
Sugar packets
Non dairy creamer (packets or bulk)
Hot water
Styrofoam cups - 8 oz size
Measuring spoons
Automatic blood pressure machines
ECK machines
CO2 measurement protocols
Digital thermometers
Devices to measure reaction time to visual or auditory stimuli
BEFORE YOU COME TO LAB
Meet with your lab group and:
1. Select a physiological variable for your investigation. Use of
the biological literature on the physiological effects of caffeine may help
you identify potential variables. Schedule your discussion early enough
in the week so you can consult with me regarding whether we have the ability
to measure the physiological variables that interest you. Please be aware
that because of health concerns we cannot measure any variable that requires
the collection of bodily fluids or tissues. We have the equipment/capabilities
to monitor the effects of caffeine on:
- Heart rate (ECG or automatic blood pressure monitors)
- Irregularity of heart rate (ECG)
- Blood pressure (automatic blood pressure monitors)
- Metabolic rate (concentration of CO2 in exhaled air)
- Ability to complete mental tasks (e.g., find words in letter puzzles)
- Reaction time in response to stimuli
- Body temperature (digital thermometers)
2. Formulate your research an null hypotheses. If caffeine affects
your physiological variable, how should the means for your treatment and
control groups compare?
3. Establish your research design. How many treatment and control
groups will you use? What will be the sample size for each group? How will
you execute the experiment?
Design Notes:
- Since people in the lab will probably vary greatly in their baseline measurements
for many physiological variables, most researchers use each individual's
change in the physiological measurement (e.g., post coffee heart rate minus
pre coffee heart rate) as the dependent variable in these types of studies.
By using the change in, say, heart rate for each subject as your dependent
variable rather than simply that person's post-coffee consumption heart
rate you often reduce the variance in the data.
- Allow at least 30 min between the ingestion of the coffee or control solutions
and the post coffee measurements.
4. Design a data sheet.
GAME PLAN
Week 1 - Data Collection
Week 2 - Data Analysis
USE OF PHYSIOLOGICAL MEASURING DEVICES
Automatic Blood Pressure Monitors
Rationale - Blood pressure measures the
pressure in the arteries at two distinct phases of the heart cycle. These
two pressures are reported as a fraction, such as 120 over 80. The systolic
blood pressure (number in the numerator) is the pressure in the artery at
the peak of ventricular contraction. The diastolic blood pressure (number
in the denominator) provides the pressure in the artery when the ventricles
are relaxed.
Procedures - Use one of the automatic blood pressure monitors to measure
your blood pressure and heart rate (pulse). I will show you how to use the
device, but remember to always use it on your left arm and to rest your
arm on the lab bench. When the machine returns your blood pressure reading
and pulse (heart rate), record these on your data sheet. To double check
the machine, take your own pulse and record that on the data sheet as well.
Always take your own blood pressure and pulse (i.e., do not have someone
else administer these tests). Contact from another individual (especially
an attractive member of the opposite sex) often affects blood pressure and
heart rate.
ECG Monitors
Rationale - Heart muscles cells possess properties of both muscle and nerve
cells. Stimulation and contraction of heart muscles results in changes in
the electrical charges across the plasma membranes of these cells. Since
bodily fluids contain high concentrations of electrolytes, the electrical
activity generated by the heart travels throughout the body and can easily
be monitored using electrodes. The graphic representation of this electrical
activity is called an electrocardiogram (ECG or EKG) and the instrument
that collects and displays this record is called an electrocardiograph.
In this lab, we will use the MacIntosh computers and MacLab devices to record
ECG's.
Interpretation of ECG's - Consult Figure 1 for an example of a normal ECG
trace. The P wave represents depolarization of the atria, the QRS complex
occurs during the depolarization of the ventricles, and the T wave represents
repolarization of the ventricles at the beginning of diastole. In our exercise
we well use the standard limb leads I. II. and III. These leads record the
difference in potential (the voltage) between the two electrodes placed
on the arms and legs. Increased cardiac rates are mainly due to a shortening
of the ventricular diastole (from the end of one QRS complex to the beginning
of the next) and only secondarily due to a shortening of ventricular systole
(measured by the duration of the QRS complex).
Procedures -
1. Turn on your Macintosh computer and click on the icon labelled "Caffeine
Lab Settings".
2. Click on "Peroni caffeine" and the computer will open your
recording page.
3. We will only use one recording so enlarge your page by moving your cursor
to the bottom of the first panel and dragging it to the bottom of the screen.
4. With subject lying comfortably on the table attach the adhesive electrode
pads to both forearms and the lower left calf (Fig 2). Connect the ECG leads
to the snaps on these pads as follows:
red lead (ground) left leg, lower calf
black lead left arm, lower forearm
white lead right arm, lower forearm
NOTE: The electrode pads must contact bare
skin.
5. Press the start icon on the computer screen and recording will
begin.
To stop recording, press the stop icon.
Print out only 2 minutes of data per person for later data analysis
NOTE: the subject must remain still and quiet while recording ECG information.
Any movement can cause great fluctuations in the electrical impulses picked
up by the leads.
6. To sharpen your image you can change the time of recording or voltage.
Both of these devises are located on upper right corner of the screen (your
right).
7. You can determine the cardiac rate by counting the number of QRS
complexes in a 10 second interval and multiply by 6 (beats per minute =
____________) Repeat this process at 10 minute intervals until resting cardiac
rate is established.
10. You can measure the variation in the time required for each complete
heart cycle by recording the time elapsed from the beginning of one P wave
to the beginning of the next P wave. Repeat this measurement for 10 complete
heart cycles.
Metabolic Rate as Measured by CO2 Production
Rationale - An individual's metabolic rate represents the rate at which
that person's cells respire reduced forms of carbon such as carbohydrates,
proteins, and fats. Cellular respiration consumes oxygen and produces carbon
dioxide as a waste product. By measuring changes in the concentration of
carbon dioxide in exhaled air, we can obtain a crude measure of changes
in metabolic rate.
In this lab we will use a color indicator to measure the concentration of
carbon dioxide in exhaled air. Phenolphthalein is pink in alkaline (basic
pH) solutions and clear in solutions with acidic or neutral pH. When dissolved
in water, carbon dioxide forms carbonic acid which can lower the pH of the
solution. By exhaling into an alkaline solution of phenolphthalein and measuring
the time needed to turn the solution from pink to clear, we can obtain a
relative measure of the carbon dioxide concentration in an individual's
exhaled air.
Procedures
1. Fill a beaker with 100 ml of 2% phenolphthalein - 0.0025 N NaOH solution.
This indicator is pink in alkaline solutions and clear in
neutral or acidic solutions.
2. Place the beaker on a white sheet of paper.
3. While sitting quietly, start a stop watch and exhale through a straw
into the solution.
4. Record the time (in min and sec) that it takes for the
solution to change from pink to clear.
Figure 3: Sample JMP data file for caffeine lab.
Figure 4: Sample JMP output with means diamonds and comparison circles.
ACKNOWLEDGEMENTS
This laboratory exercise was inspired by the teaching of Dr. Alastair Inman
at Knox College. The current handout represents an amalgamation of handouts
authored by Dr. Patricia Peroni and Dr. Carole Lewis. Figures 3 and 4 were
copied from Spence and Mason (1992).
REFERENCES
Flenley, D. C. 1983. Ventilatory response to O2 and CO2 during exercise. Annual Review of Physiology 34:415
Guz, A 1975 Regulation of respiration in man. Annual Review of Physiology 37: 303.
Hasenferatz, M. 1992 Action Profiles of Smoking
and Caffeine: Stroop effect, EKG and peripheral physiology. Pharmacological
Biochemical Behavior 42: 42
James, J. 1991 Pressure effects of caffeine and cigarette smoking, British Journal of Clinical Psychology 30.
Spence, A.P. and E.B. Mason. eds. 1992. Human Anatomy and Physiology. 4th
ed. Saint Paul, MN: West Publishing Co.
