The Effect of Caffeine on Heart Rate
Mark Cruz

Introduction: Caffeine is a trimethylxanthine, with the chemical formula of C8H10N4O2. It works by decreasing adenosine levels in the brain by attaching to adenosine receptor sites in the nerve cells. When dopamine can’t attach, the body doesn’t feel tired. Also, the increased level of brain activity caused by caffeine triggers the release of adrenaline. Adrenaline generally has the following side effects on the body: dialated pupils, increased heart rate, increase in blood pressure, and a release of sugar into the bloodstream for increased activity.  It is estimated that the half life of caffeine is approximately 6 hours. Caffeine, like many other drugs, is addictive. A typical can of Mountain Dew has 55mg of caffeine per 12 oz can. Data on Mountain Lightning was not available.

Problem:  What are the effects of Mountain Dew and Mountain Lightning on the human heart rate?

Hypothesis:  If an individual consumes 12 oz. of Mountain Dew, his or her heart rate increase will be greater than that of a person who drinks a can of Mountain Lightning, due to the fact that Mountain Lightning most likely contains a lower concentration of caffeine than Mountain Dew.

Variables: Independent: Type of Soda Drank
                 Dependent: Heart Rate Increase
 
Materials:  2 cans of Mountain Dew				2 cans of Mountain Lightning
                  CBL						calculator
                  Watch

Procedure:  
	Note:  Caffeine intake should cease the night before the experiment is to be administered.

1.	With 5 people, calculate each person’s resting heart rate using the CBL and also take each person’s resting pulse manually.  See directions for CBL.  Record.
2.	Two people drink 1 can each of Mountain Dew.  Two people drink 1 can each of Mountain Lightning.  The fifth should not drink anything because he is the constant.
3.	Set up the CBL and equipment according to the attached CBL sheet.
4.	Ten minutes after each person finishes his can of soda, calculate the heart rate using the CBL, and also take each person’s pulse manually.  Record and compare results.

	Mountain Dew	Mountain Lightning	
	Resting HR (bpm)	Caffeine HR (bpm)	% Heart Rate Increase	Resting HR (bpm)	Caffeine HR (bpm)	
Julenne/Richard	57	53	7	58	71	
Mark/Alex	51	68	33	59	87	
Constant (Leah)	69	----		75	---	
Mountain Lightning     % Increase	
Richard	22.4	
Alex	47.5	
		
`

	Resting Pulse (bpm)	Caffeine Pulse (bpm)	
Julienne (Mountain Dew)	68	53	
Leah (Constant)	76	70	
Mark (Mountain Dew)	65	53	
Richard (Mountain Lightning)	67	63	
Alex (Mountain Lightning)	76	74	

Conclusion: 
	The Results of our Experiment showed that the participants who drank Mountain Lightning had a greater increase in their heart rates than those who drank Mountain Dew. This would normally lead us to conclude that Mountain Lightning has more caffeine than Mountain Dew; however, there were several factors which may have skewed our results. First, there was excessive talking, movement, and laughter during the test.  Also, several individuals in the test group consumed high levels of caffeine on a daily basis either at work or while playing sports. This would decrease the effect of caffeine on these people. These variables could have increased the heart rate of those who did it. Also, the pulse that was taken manually was different than that collected from the CBL.
	If given the opportunity to perform this lab again, one should take multiple samples of the subjects’ heart rate over time. This experiment only took once sample 10 minutes after initial caffeine consumption; however, it would have been better to do multiple samples with intervals of 5 minutes between samples. This would have provided a more accurate reading. Furthermore, the amount of talking, movement, laughter, and other things that would increase heart rate should be limited to a bare minimum.