How Caffeine Effects Heart Rate

Scientific Study, 2012

12 Pages, Grade: 95



Background Information: The human heart is a major muscular organ located in the thoracic cavity between the lungs. Its major function is to pump blood throughout the body. A double-layered sac, Pericardium, which is the tough connective tissue protects and anchors the heart. There is fluid between the layer of the sac allow for lubrication of the heart’s continual motions. The inner layer of the sac is the heart wall, which is mainly cardiac muscle. The human heart is made up of two chambers. The atriums receive blood from veins, and the ventricles pump blood into the arteries. For the blood to pass through the an atrium to a ventricle for example, the blood has to pass through a heart valve. Valves control the blood from moving backwards. The “lub-dub” sound made by a beating heart derives from the closing of the atrioventricular (AV) valves, then the concurrent closing of the aortic and pulmonary valves (Starr, 2007). The human heart is also myogenic meaning the heart is independent of an outside stimulus from the nervous system. The sinoatrial (SA) node, pace maker, is responsible for sending electrical impulses through the heart making it contract and pump blood. The human heart is very much affected by the consumption of caffeine. Caffeine can be found in certain coffees, teas, sodas, and chocolates. By consuming caffeine one’s heart rate to dramatically increase and also cause abnormal heart rhythms (Medline Plus: Caffeine, 2012).

Problem Question: What is the effect of caffeine from coffee, herbal tea, and black tea on heart rate?

Hypothesis: If a human consumes a beverage containing a higher concentration of caffeine, then the heart rate will be higher than consuming a beverage with a lower concentration of caffeine.

Hypothesis Explanation: This is because caffeine is a stimulant. Stimulants change the way the brain works by changing the way nerve cells communicate. Nerve cells, called neurons, send messages to each other by releasing chemicals called neurotransmitters. Neurotransmitters work by attaching to key sites on neurons called receptors. Stimulants can also cause the body’s blood vessels to narrow, constricting the flow of blood, which forces the heart to work harder to pump blood through the body. The heart may work so hard that it temporarily loses its natural rhythm (Stimulants, 2012). A normal resting heart rate for adult’s ranges from 60 to 100 beats a minute. In most cases, a lower heart rate at rest implies more efficient heart function and better cardiovascular fitness. For example, a well-trained athlete might have a normal resting heart rate closer to 40 beats a minute (Caffeine content for coffee, tea, soda and more, 2011). Additionally caffeine blocks the enzyme phosphodiesterace, which normally activates production of an enzyme, cyclic AMP (cAMP), this initates a protein that increases heart rate. The heart rate is regulated as cAMP is kept in a drug free cell. When caffeine is introduced, cAMP is eliminated, placing the protein (PKA) into overdrive. Therefore, heart rate is increased when caffeine is consumed (Caffeine Pharmacology, 2012). Nonetheless a beverage with more caffeine will lead to a greater amount of heart rate in beats per minute (bpm±1.0bpm) as compared to a beverage with less caffeine.


Dependent: Number of heart pulse rate in beats per minute (bpm±1.0bpm). This measurement will be taken by placing the index and middle finger on the neck pressing gently on the carotid artery, ten minutes after the consumption of either caffeinated coffee, herbal tea, or black tea, and counting the heart rate over the course of one minute.

Independent: Amount of caffeine found in 250ml of either caffeinated coffee, herbal tea or black tea.


Table 1. Controlled variables kept constant

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Experimental Control: The experimental control is the number of heart pulse rate in beats per minute (bpm±1.0bpm) after an hour of physical rest. The experimental variables do not effect the experimental control. The experimental control is to be used in comparison against other trials with physical activity.


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How Caffeine Effects Heart Rate
State University of New York at Stony Brook
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caffeine, effects, heart, rate
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Tracey Rosenlicht (Author), 2012, How Caffeine Effects Heart Rate, Munich, GRIN Verlag,


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