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PHYSIOLOGY EXPERIMENTAL DESIGN: EXAMPLE

Research QuestionWhat is the effect of change in concentration of caffeine in Lipton “Yellow Label Tea” on heart beat per minute of homo sapiens measured through the manual measure using fingers on the carotid artery?

Background KnowledgeHeart is a major muscular organ located in the chest between the lungs and is

responsible for pumping blood throughout the body. In humans it is myogenic, meaning that it is independent from the nervous system. The heart is made up of two atriums, which receive blood from the veins and two ventricles, which are pumping blood into the arteries. It is divided into two chambers, each consisting one atrium and one ventricles. Valves are responsible for preventing blood from flowing backwards. One of the major valves are located between the atriums and the ventricles. The pacemaker, also known as the sinoatrial node is responsible for pumping blood through the heart, by contracting it. (“The heart”)

A regular heart rate for an adult person ranges between 60 and 100 beats per minute. Lower heart rate usually implies more efficient heart function.For example, a well-trained athlete can have a heart rate as low as 40 beats per minute. (Rosenlicht, 2012)

Caffeine is a stimulant drug, found in the leaves, seeds and fruits of some plants. It also increases the reward-memory of the pollinators. The primary consumers of the caffeine are humans. It acts as a central nervous system and metabolic stimulant. It increases focus, concentration and decreases drowsiness. Stimulant drugs change the way the brain works by changing the way the nerve cells communicate. These nerve cells, also called neurons, send messages by releasing chemicals called neurotransmitters, which work by attaching on the key sites of nerve cells. Stimulants also often constrict the blood flow by narrowing the blood vessels. This causes the heart to work harder in order to maintain the blood supplies to all the organs. Consuming caffeine increases one’s heart rate and can also cause abnormal heart rhythms. (“Caffeine: MedlinePlus”, 2012).

“Yellow Label Tea” is a brand of black tea produced by Lipton. It is one of the most widespread and famous types of tea in the world. A cup of this kind of tea (236 mg) consist 55 mg of caffeine. ("Black Tea: MedlinePlus Supplements.") Caffeine is also sold in the pharmacies, usually in the form of pills, which are made 50% of caffeine benzoate and 50% of sodium benzoate by mass. In order to obtain the solution of caffeine benzoate with a concentration similar to the the concentration in a regular teacup, we will need to dissolve a 0.2g pill in 454 ml of water. (Caffeine Informer)

It takes around 15-20 minutes before the effects of caffeine are realized, if it is consumed in the form of tea or coffee. 99% of the caffeine is absorbed through the membranes in only 45 minutes. In human, the half-life for caffeine is between 2.5 and 4.5 hours, which explains why an average effect of tea of coffee lasts about 2 to 3 hours. ("Caffeine Metabolism.")

HypothesisA person who has consumed tea with a higher concentration of caffeine is more exposed to its effects, therefore, their heart rate will increase more than the heart rate of a person who has consumed tea with a lower concentration of caffeine.

VariablesIndependent VariableThe independent variable for this experiment was the concentration of caffeine in 250 ml of the Lipton “Yellow Label Tea., alternated through the change in concentration. The concentration of caffeine was changed by varying the amount of teabags added to the different solutions of tea.

# of beaker Contents Concentration of Caffeine (mg/100mls)

1 Decaffeinated tea (4 tea bags)in 1 liter of water

2.0

2 “Yellow Label Tea” (2 tea bags) in 1 liter of water

11.0


22.0


33.0


44.0

6 1 liter Caffeine and Sodium benzoate solution

22.0

7 1 liter Sugarpill solution 0.0

Groups # 1, 6 and 7, who were given the contents of the corresponding beakers were the control groups.In order to distinguish the effect of the action of drinking tea with the effect of caffeine, Group # 1 was served a decaffeinated tea. It has a slightly different taste to the actual “Yellow Label Tea”, however, it contains nearly no caffeine, which allows us to measure the effect of the actual process.Group # 6 was given a solution of caffeine benzoate in order to measure the effect of caffeine, without the effect of drinking tea.Group # 7 was introduced in order to control the effect of drinking a solution itself, rather the effect of actual pill. Solution in the beaker # 7 contains no caffeine at all.

Dependent VariableThe dependent variable for this experiment was the heart rate measured by using fingers on the carotid artery. It is measured in bpm, +/- 1.0 bpm. Heart rate was measured immediately before the intake of the tea/solutions, and 6 times after the intake, with the intervals of 5 minutes. Participants were asked to count the number of heartbeats during the 15 seconds. the number is needed to be multiplied by 4, in order to receive a result in bpmExample:A participant has counted 20 beats in 15 seconds.20x4=80bpm.

Controlled Variables

Why was it needed to be controlled?

How was it controlled.

Type of tea Different types of tea contain different amount of caffeine, and therefore will affect the volunteers with different intensity. Additionally, other supplements may affect the heartrate of the participants.

Lipton Yellow Label Tea was chosen as a type of tea used for the experiment, because it is one of the most commonly used and it does not (according to the manufacturer) include any special add-ons, including the taste-related. Decaffeinated tea was introduced as a control variable. It contains almost no caffeine and therefore can be used to check if the process of drinking tea affects the heart rate of people.

Weight of the participants. The effect of caffeine increases as the body mass of the participator decreases. A greater mass means a greater body weight, which results in a more diluted caffeine. ("Caffeine Metabolism.")

In order to avoid this effect, only the volunteers with the body weight between 70 and 80 kg were allowed to participate in the experiment.

Time of infusion Time that the tea bags are kept in the water may affect the concentration of caffeine, because it is given more time for diffusion of caffeine from tea leaves to water. ("Black Tea: MedlinePlus Supplements.")

Teabags were held in the beakers for 5 minutes, measured by an accurate stopwatch (s +/- 0.01s).

Temperature of the Tea A very hot liquid can burn the participants. This pain can cause their heart rate to increase. However, a very low temperature could be disliked by the participants, and therefore, also increase the participant’s heart rate.

Thermometers were kept in the beakers, in order to control the temperature. Only when the temperatures are around 40°, the tea is served.

Time of measurements The longer time of measurements will guarantee the more accurate measures, however, it will give more time for caffeine to take effect.

All heart rates were measured for 15 seconds.

Time between the intake of caffeine and the measurements

Caffeine needs time to be metabolized and cause a measurable change in the heart rate of the person. Usually caffeine causes ("Caffeine Metabolism.")

The observations were taken repeatedly, over the period of 30 minutes with 5 minutes intervals. This will assure that the effect of caffeine is fully measured. (Caffeine metabolism)

Age of the participants Caffeine may affect people differently depending on their age. A younger population is more affected by it, as their bodies aren’t fully developed yet. ("Actions of caffeine…”, 1999)

For this experiment, young people between the age of 18 and 20 were chosen, as they are one of the biggest target populations of the caffeine-based products.

Gender of the participants Caffeine, as well as other stimulants may cause different effect in males compared to females, because of their body type, usually affecting the females stronger.

Only males were allowed to participate in this experiment. In order to examine the dependence of gender in the caffeine affecting the heart rate, another experiment could be performed, with gender as an independent variable.

Diet of the Participants Caffeine, other stimulants or drugs and food consumed before the experiment could affect the participants reaction to caffeine.

All the participants were asked to come to experiment early in the morning and not eat or drink anything before that. Participants who are obliged to take medicine in the morning were not allowed to participate.

Uncontrolled Variables

Physical and mental state of the participants.

Other factors may affect the heart rate of the participants, such as stress, amount of sleep, tiredness and other food and drinks consumed by the participants.

All participants were asked to come to the experiment right after they wake up, without having a meal. They were also obligated to answer the question whether they did face a high amount of stress or physical activity in the recent past.

Placebo effect Because most people are familiar with tea, the can recognize it by its taste. Their heart rate can increase because of the placebo effect: participants think that their heart rate should increase, and it increases.

In order to examine this effect the control groups were introduced. This was a singe-blind experiment: participants did not know which group there are in.

Excitement about tea Another reason for an increase of the in heart rate during the experiment can be the excitement about the tea. People might enjoy the actual taste about the tea, which could raise the heart rate independently from the effect of caffeine.

In order to exclude the opposite, the excitement about tea, the control groups were introduced.

Accuracy of the heart rate measures

Because the participants were measuring their own heart rate, they might have made mistake, or did not start at the right time, or did not count the first and/or last beats. This had to be done in order to prevent the stress from other people putting fingers of the participant's neck.

All participants were timed simultaneously and explained and shown how to measure their heart rate before the experiment was taken.

Disgust about tea If the volunteer does not like tea, his heart rate may increase independently from the effect of caffeine.

All the participants were asked to answer the question whether they are common consumers of tea. Only the participants with regular tea-drinking experience were selected for the experiment. This assumes they are comfortable with tea’s taste. However, not milk or sugar were available for the participants, because this would mean adding another uncontrolled variable: the effect of sucrose on heart rate.

Biological variance between participants

Caffeine may affect people in different way, even if they have similar characteristics, such as body weight and gender, the speed of their metabolism may differ.

For this experiment, the participants were asked to fill in the questionnaire. Only the people with specific characteristics were selected.

Random variance in the tea solution

Because of the homogeneous nature of tea, some precipitate is formed after some time. The concentration of caffeine may vary within the solution.

In order to decrease the effect of random variance, all of the solutions were stirred before pouring into the cups.

Room temperature Room temperature can affect several important things within the experiment. First of all, a very high or low temperature may cause discomfort to the participants by itself, and therefore cause theIr heart rate to increase. It may also affect the temperature of the tea and the speed of metabolic processes within the bodies.

In order to decrease the effect of the room temperature, all experiments were performed simultaneously, on the same day at the same time.

Apparatus and Materials ● Cooking gloves● 5 Tea kettles (1.5l)● 20 Lipton “Yellow Label Tea” Teabags● 4 Teabags of Caffeine-free tea● 10l of water● 3 0.1g “sugarpills”● 3 0.2g Caffeine and Sodium Benzoate Pill Figure 1. Picture of

Lipton ● 2 stirring rods Yellow Label Tea● Stopwatch (s +/- 0.01s)● 30 paper cups (250 cm3)● Graph for observations (Example provided below)● 5 1000ml beaker (+/- 10cm3)● 2 2000ml beaker (+/- 20 cm3)● 500ml beaker (+/- 5 cm3)

MethodSelecting the participants

1. Make a survey, that includes the questions asking about participant’sa. Ageb. Genderc. Body weightd. Regularity of the consuming teae. Regularity of consuming caffeine in forms other than tea

2. Select 35 participants that match the following standard:a. Between 18 and 20 years oldb. Malesc. 70-80 kg.d. One or more cups of tea consumed daily

3. Ask the participants to come to the place of the experiment on the correct day, right after they wake up and not to eat or drink anything before the experiment.

Preparing the tea1. Label the beakers 1-7 (1000ml are 1-5 and 2000ml are 6-7)2. Measure around 1.1l of water and pour it into the teakettles. 3. Repeat the step #1 for the other 4 teakettles.4. Boil the teakettles 5. Pour 1 liter of water from one of the teakettles into a beaker #1. 6. Repeat the step #7 for the tea kettles # 2, 3, 4 and 5, pouring them into the beakers # 2,

3, 4 and 5 respectively..7. Add the teabags to the according beakers. Make sure to do this simultaneously. Start

the stopwatch).

a. Add 4 teabags of the caffeine less tea into the beaker #1b. Add 2 tea bags of the Lipton “Yellow Label Tea” Teabags into the beaker #2c. Add 4 teabags of the Lipton “Yellow Label Tea” Teabags into the beaker #3d. Add 6 teabags of the Lipton “Yellow Label Tea” Teabags into the beaker #4e. Add 8 teabags of the Lipton “Yellow Label Tea” Teabags into the beaker #5

8. Place the thermometer inside the beakers.9. After 5 minutes (measured by the stopwatch), remove the teabags.10. Start the stopwatch again

Preparing the caffeine benzoate solution1. Add 1365 ml of water to the 2l beaker, using a 500ml beaker.2. Put a 3 caffeine and sodium benzoate pills into a 2l beaker.3. Slowly stir the solution.4. Pour 1000 ml of the solution into a 1l beaker #6

Preparing the placebo solution5. Fill the beaker #7 up to a one liter mark.6. Put a 3 sugarpills into a 2l beaker.7. Slowly stir the solution. Use a different stirring rod.

Preparing the servings1. Wait until 10 minutes have passed. Reset the stopwatch.2. If, due to the high room temperature, the cooling rate is too slow and the liquid does not

reach 40 degrees Celsius in 10 min, u can wait extra time.3. Label the cups 1-7. There should be 5 cups with every number.4. Pour the solutions from the beakers to the according cups. There should be 200 cm3 in

each cup.5. Randomly separate the participants into 7 groups, 5 people each.6. Measure the heart rate of the participants.

a. Ask them to place their fingers on their neck and find the carotid artery. b. Tell them to start counting the beats. Start the stopwatch.c. After 15 seconds, tell the participants to stop counting and record the data.

Conducting the experiments1. Assign numbers to the groups. 1 to 7.2. Distribute the cups.3. Ask the participants to drink the entire tea or the solution and start the stopwatch.4. Ask the participants to wait for 30 minutes. They are allowed to sit, walk and talk, but not

to do any heavy physical activity. During this time, make them measure the heart rate every five minutes as described in steps # 5 and 6.

5. After five minutes, measure the heart rate of the participants. Ask them to place their fingers on their neck and find the carotid artery.

a. Tell them to start counting the beats. Start the stopwatch.b. After 15 seconds, tell the participants to stop counting and record the data.

6. Repeat the step 5 5, 10, 15, 20, 25 and 30 minutes after the start of the experiment.7. Insert the data in the table.

Thank the volunteers and tell them that they are free to go.

Raw Data TablesGroup # 1.

Participant #

Measurement of the heartrate before the drink(bpm +/- 1.0 bpm)

Measurement of the heartrate 5 minutes after the drink(bpm +/- 1.0 bpm)






1

2

3

4

5

Group # 2.

Participant #








1

2

3

4

5

Group # 3.

Participant #








1

2

3

4

5

Group # 4.

Participant #








1

2

3

4

5

Group # 5.

Participant #








1

2

3

4

5

Group # 6.

Participant #








1

2

3

4

5

Group # 7.

Participant #








1

2

3

4

5

References

"Black Tea: MedlinePlus Supplements." U.S National Library of Medicine. U.S. National Library

of Medicine, n.d. Web. 31 May 2014.

"Caffeine Absorption." Caffeine Informer. N.p., n.d. Web. 30 May 2014.

"Caffeine: MedlinePlus." U.S National Library of Medicine. U.S. National Library of Medicine,

n.d. Web. 29 May 2014.

"Caffeine Metabolism." Caffeine Inforemer. N.p., n.d. Web. 29 May 2014.

"The Heart (Human Anatomy): Diagram, Definition, Location in the Body, and Heart Problems."

WebMD. WebMD, n.d. Web. 29 May 2014.

"Lipton Tea." Caffeine Informer. N.p., n.d. Web. 29 May 2014.

Tracey Rosenlicht , 2012, How Caffeine Effects Heart Rate, Munich, GRIN Publishing GmbH,

http://www.grin.com/en/e-book/207849/how-caffeine-effects-heart-rate

Fredholm BB, Bättig K, Holmén J, Nehlig A, Zvartau EE (1999). "Actions of caffeine in the brain

with special reference to factors that contribute to its widespread use". Pharmacol. Rev. 51 (1):

83–133.

Nurminen, M., Niittynen, L., Korpela, R., & Vapaatalo, H. (1999). Coffee, caffeine and blood

pressure: a critical review.European Journal of Clinical Nutrition, 1. Retrieved May 20, 2014,

from http://www.nature.com/ejcn/journal/v53/nfyn

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