Regular use of upwards of 350 mg of caffeine a day causes physical dependence on the drug. This means that interruption of the regular use produces a characteristic withdrawal syndrome, the most conspicuous feature of which is an often severe headache that can be relieved by taking caffeine. Absence of caffeine also makes regular uses feel irritable and tired. (6)
Caffeine and health problems.
Heartburn – in some people, coffee has been shown to relax the sphincter muscles at the lower and of the oesophagus, allowing the stomach contents to “back up” into the oesophagus: this is called heartburn. Caffeine alone has no effect on the sphincter muscles, so other substances in coffee apparently cause the heartburn.
Ulcers – caffeine can increase the secretion of both acid and pepsin in the stomach, which could exacerbate an existing ulcer. However, since both “regular” and decaffeinated coffees have also been shown to stimulate the gastric mucosa and increase stomach acid secretion, caffeine is probably not the only component of coffee responsible.
Heart problems- caffeine has been shown to cause cardiac arrhythmias (irregular heartbeats) in certain individuals; often persons with heart disease are told to avoid caffeine altogether. However, no evidence shows that caffeine is a causative factor in the development of heart disease. (5)
Blood Pressure – caffeine use may increase blood pressure. The amount of caffeine in 2-3 cups of coffee can raise systolic pressure 3-4 millimetres of mercury 9 (mmHg) and diastolic pressure 4 to 13 mmHg in people without high blood pressure. Among people who don’t consume caffeine regularly it can cause a temporary but sharp rise in blood pressure. Exactly what causes this spike in blood pressure is uncertain. Some researches suggest that caffeine narrows blood vessels by blocking the effect of adenosine, a hormone that helps to keep them widened. Caffeine may also stimulate the adrenal gland to release more cortisol and adrenaline, which cause blood pressure to increase. (4)
Brain and behaviour – caffeine stimulates the brain and behaviour. Use of 75-150 mg of caffeine elevates neural activity in many parts of the brain, postpones fatigue, and enhances performance at simple intellectual tasks and physical work that involves endurance but not fine motor coordination. (6)
Sleep – the effects of caffeine on sleep are clear-cut: taken before bedtime, it usually delays sleep onset, shortens overall sleep time, and reduces the “depth” of sleep. After using caffeine, sleepers are more easily aroused, move more during sleep, and report a reduction in the quality of sleep. The effects of dreaming are less clear.
(6)
The most common medicinal use of caffeine is a part of headache and other pain relievers. Caffeine is added both for its specific ability to relieve headache, including that caused by caffeine withdrawal, and for its ability to help analgesics do their work better. The ability of caffeine to stimulate breathing is used in the treatment of apnoea (cessation of breathing) in newborn babies, and as an antidote against the depression of breathing by overdose of heroin and other opiate drugs. More controversial therapeutic uses of caffeine are theses: to kill skin funguses; to improve sperm mobility; to enhance the toxic effects of chemicals used in cancer therapy; and to facilitate the production of seizures during electroconvulsive therapy. (6)
All these factors put together create a very interesting study of the chemical, caffeine. The effects of caffeine, being so diverse, made me think that it would be interesting to see how caffeine would effect my blood pressure, pulse rate and reflex action. I believe that the more caffeine that is consumed the more it will increase the pulse rate, which means the oxygen and glucose goes to create energy reaching the muscles quicker. For this to happen my pulse rate and blood pressure has to rise, therefore the caffeine will increase the rate of respiration, which will prepare the muscles ready for contractions. The more caffeine I will consume the shorter the reflex action will be and I will be able to respond to a stimulus faster. The reflex action will decrease because of the increase of speed of neurotransmitters in the body.
Method
- Before the experiment, carry out the reflex action with the ½ meter ruler a couple of times. (This is so that the experiment will be fair and un-practised and the results would be due to the effect of the caffeine).
- With the automatic digital monitor take a blood pressure at rest. Record the results.
- Take the radial pulse rate with fingers at rest. Record the results.
- Take 5 reflex measurements. Record and calculate the average result.
- Start time. Drink one cup of coffee (made with 1 teaspoon of coffee) and then allow 5 minutes for it to take effect and enter into the bloodstream. Re-record 3 reflex measurements and then measure the pulse rate with your fingers. (Calculate the average result of the reflex actions).
- Repeat reflex and pulse rate measurements after another 15 minutes.
- Allow 30 min from the start time. Then have another cup of coffee, which is the same strength as the first.
- After 5 min record 3 reflex measurements and pulse rate again (calculating the average of the reflex action).
- After another 15 min take the last 3 reflex measurements (don’t forget to calculate the average), pulse rate and blood pressure.
- Record all the results accurately into the table.
To make this experiment fair I will:
- Make sure that it is the same amount of caffeine used every time by using the same teaspoon and the same type of coffee. If there are different amounts of caffeine then the results will not be precise and the experiment will not allow a fair comparison.
- The results are recorded at the same time after the caffeine has been consumed. On average, this should be no less than 30 seconds – and ideally as soon as possible.
- Sit during the whole experiment to limit the change in pulse rate and blood pressure.
- Measure and record the results accurately.
- It is important to be careful with caffeine because it can have different effects on the body – some of which are very dangerous. Caffeine increases heartbeat, respiration, metabolic rate and the production of stomach acid and urine. The effects vary among people and may depend upon the person’s sensitivity to caffeine, their metabolism or upon whether the person regularly or occasionally has caffeine.
- Use an automatic digital monitor to measure the blood pressure, this will give more accurate results.
- Keep the noise at a minimum level, because it can affect the pulse rate.
If I make sure I do all of these things accurately as listed, the results will be fair and far more precise – and the experiment will have a far better chance of succeeding.
Results
Here are the results showing the effect of caffeine.
Analysis
My graph clearly shows an increase in my pulse rate. My pulse rate increases straight after the first cup of coffee (after 5 min) and then gradually decreases. This is because the caffeine is a stimulant and it causes the heart to beat faster.
The blood pressure after the experiment gradually decreased. My prediction before the experiment was that the blood pressure would increase but in my results the caffeine had a calming effect on me. It might be because I never normally drink coffee and my body is not used to the effects of the caffeine.
The graph shows that my reflex action got faster with the caffeine in my system.
Discussion
Different people have different metabolisms and tolerances to drugs and chemicals, this is why the results of the experiment varied from person to person: for some of them blood pressure, pulse rate and reflex action increased, for others it decreased. Some of the participants were non-coffee drinkers, others – occasional coffee drinkers. A person who consumes caffeine occasionally may drink several cups of coffee a day and notice little effect or none, whereas a person who is non-coffee drinker may feel some stimulant effect after just one serving.
Overall, the reflex action speed gets faster because of the increase of speed of neurotransmitters in the body. Neurotransmitter substances need calcium, which causes the vesicles to move from the centre of the pre-synaptic ganglion to the pre-synaptic membrane and fuse it. Then the vesicles release the transmitters into the synaptic cleft. Due to diffusion the neurotransmitters are picked up by receptor molecules, which causes the impulse to travel along the post-synaptic ganglion. Caffeine speeds up this process – thus giving a faster reaction time.
Caffeine increases the pulse rate because it increases the strength and frequency of heartbeats and the body needs more oxygen, which gives us energy. To get this extra oxygen the heart needs to pump faster to get the extra oxygen into the blood. The blood is pumped around the body faster therefore giving a faster pulse rate.
Generally when the pulse rate increases, blood pressure rises and so the amount of blood pumped out of the heart with each beat. Higher blood pressure helps to drive blood flow around the body. The heart becomes stronger and larger so it can pump more blood through the body with every beat and sustain its maximum level with less strain. The blood pressure after consuming caffeine fell, because less effort is needed to pump blood.
All of these changes vary considerably among people and may depend upon the individual’s sensitivity to the caffeine, their metabolism, or upon whether the consumer habitually uses or rarely uses caffeine.
Evaluation
My overall results were quite good. There still might be the possibility that they are not quite perfect. For example, to get better results I would have done the experiment more times to get a much better average. Thoughts or laughter can alter the pulse rate, so maybe getting myself to concentrate and keep my thoughts or emotions from affecting the results. The pressure of getting the readings and results done in a set of time can increase adrenalin levels, which would increase pulse rate. The varying presence of food in my stomach could alter the absorption of the caffeine into blood stream. I may have got better at catching the ruler by the process of repetition (practice). The measuring of the point on the ruler where I caught it is not really very accurate.
To improve my results it may be better for all the participants to refrain from having any caffeine for a set period before the experiment (for example 12 hrs). It would be better to conduct the experiment in a more relaxed environment with no pressure or stress and no noise. All these things can affect the overall results.
Taking all these factors into account the results obtained gave a satisfactory connection between blood pressure, pulse rate, reflex action and amount of caffeine consumed.