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The affect of Caffeine on pulse rate

Categories: Caffeine

Stimulants are a class of drug that boosts, alternates and increases your energy levels and they activity of the nervous system. Caffeine is in drinks, such as; Coca-Cola, tea and coffee, these are called caffeinated drinks. Caffeine is not normally recognised as a drug to most. Caffeine has an effect on your heart rate, (this is how fact your hear beats) Caffeine is able to change the way your body and mind works Chocolate is known to have traces of caffeine in it also

The aim What is the point this experiment;-
My aim in this experiment is to see what effects caffeine is prone to on the heart rate, Also to compare someone’s heart rate who has consumed caffeine to someone’s who hasn’t.

This should give us a developed idea to the effects of caffeine. In this experiment there will be several variables;-

The independent variable;-this is the variable I will be changing, this is the number of people of which are drinking the caffeine and the ones who are not.

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The Dependant variable;-This is the variable we measure, I’m measuring the persons heart rate, then working out the difference to show what effects caffeine is likely to have on the heart rate. Controlled variables;-

The following variables I am keeping the same;-
Room temperature
The volume of the drink
No-one will consume caffeinated food or drinks beforehand.

From what information I have collected I predict that the pulse rate of the people drinking the caffeinated drinks will have an increased pulse, because as research shows, caffeine is a stimulant.

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Therefor the prediction of an increased heart rate when caffeine enters the blood stream seems reliable. I also think after a certain period of time, when the caffeine has left the persons system that the heart rate will lower again.

Caffeinated Or Not?

What will I do? How will I do it?
Method;- you will need…
Six cups
A bottle of a caffeinated drink
A bottle of a de-caffeinated drink
Heart rate monitor or a simple stop watch
A table of results to record your data
Steps;- What am I going to do?
1) Prepare 6 people to take part in the experiment.

2) Make each person sit down for 15 minutes in order to calm their heart rate. 3) Pour the caffeinated drink into three cups of a 300 cm cubed volume. 4) Pour the de-caffeinated drink into another 3 cups of the same size. Making sure that the people participating in the experiment do not see which drink they are being given( Blind testing) 5) Take each person’s heart rate and record it in a table. This is the starting point 6) Give each person their drink, still making sure you carry out a blind test. 7) Take each person’s heart rate every 30 seconds; continue to do this for a further 5 minutes. 8) After 5 minutes, take one final heart rate, this will help with your results. 9) Create a table of results to hold your information in, make sure the table is clear to read and easy to understand. 10) Work out the difference between everyone’s heart rate

Method 2;- Shortened version;-
1) Prepare six people for the experiment by making each person sit down for 15 minutes to calm their heart rate. 2) Pour a caffeinated drink into 3 polyester cups of a 300cm cubed volume. 3) Do the same with the de-caffeinated drinks.

4) Label the caffeinated drinks ‘a’ and the de-caffeinated drinks ‘b’, so you won’t mix them up, but don’t let the participants know which label represents which drink. 5) Take each person’s heart rate; this is your starting point. 6) Give each person their drink, at random.

7) Take each person’s heart and record it in a table of results, do this every 30 seconds for a further 5 minutes. 8) With your results fill in your table and work out the difference between the heart rates, this should indicate the heart rates affected by caffeine.

About my graph;-
The graph I used for this experiment is a line graph; it shows various results of different pupil’s heart rate. The lines on the graph are all unique; some have a sudden increase in heart rate whilst others have not. Pupil one;- which is the pink line had a base rate of ‘72’ this remained constant throughout the experiment, only rising and falling by a small few. However pupil two had a base rate of ’78’ but after drinking the drink at around 8-9 minutes the heart rate increased dramatically. Overall 3 results (pupils 1,3 and 5) practically remained the same, whilst the other three (pupils 2,4 and 6) had several increases whilst the drink being in their system. Summing up my results;-

We know from research that caffeine is a stimulant and stimulants affect the pace of your heart. So the three results that have a big increase in their heart rate, seem to show that they had caffeine in their system. However we did discover an anomaly, after 8 minutes pupil two’s heart rate had a dramatic increase. This may well have been the caffeine but it’s more likely to have been caused by something called a ‘placebo’ effect.

This is when the pupil consuming the drink in the experiment got excited and this is what made the sudden increase in the pupil’s heart rate. After two minutes pupil four’s heart rate increased also, however this time, the increase remained constant for a further two minutes before starting to drop again. This state a more obvious term of the effect of caffeine. The graph clearly shows which results are the ones effected by caffeine, and the ones which are not. Amendments;- what I can I do better next time?

In future experiments like this one, I think I would make sure that no-one involved in the experiment eats or drinks any caffeinated products before taking part in the experiment. This ensures us that their heart beat is at its normal pace. Because talking and movement can affect how our hearts beat I would also make sure that everyone in the experiment sits down for a longer period of time that was done before.

This helps the heart lower to its base rate. Our results weren’t really valid because we were unable to control our controlled variable, this may be because the person who had consumed caffeine insisted on talking to everyone else, so this would have increased the other people’s heart rates also. In future experiments we can delay this by keeping people apart after taking part in the experiment, this way they cannot influence each other’s behaviour. Research has shown us that caffeine on average takes around 45 minutes to enter the blood stream, so we cannot be certain our results were due to the effects of caffeine.

This could be amended by measuring the pulse rate over a longer time span, so the caffeine had longer to affect our pulse. In the experiment I chose to measure my pulse over a period of two minutes, next time to show more valid and reliable results I would measure my heart rate over shorter intervals. Finally one more improvement would be to test more caffeinated drinks with our pulses, so then we can rule out the thought off the results being due to glucose or so on, we then can be sure its definitely caffeine that’s increasing out hear rate. Conclusion;- what do I think?

From this experiment I can conclude that caffeine can affect different people in different ways, depending on their diet, sex and size. Whether they are used to drinking caffeine constantly and how much their body can take of it. My prediction on average was correct as I suggested that the people with caffeine in their system were most likely to have a higher heart rate. This was mainly correct, but I was shocked to find out that my results were not valid due to the length of time caffeine takes to enter the blood stream.

An example of caffeine being used may be when an athlete drinks a caffeinated drink before they take part in their sporting event, the effect would be the increase in their pulse and more energy would be dispersed in the body. Personally I don’t think this is fair, as I previously said caffeine effects different people in different ways, so caffeine could have a strong effect on certain people, whilst it has a less strong effect on others. This affects the balance of the game and it’s not natural energy being used in the event. This could be classed as cheating.


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The affect of Caffeine on pulse rate. (2016, May 13). Retrieved from

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