The Effects Of Dehydration And Rapidly Consuming Water Biology Essay

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Blood pressure measures the pressure applied against the inner walls of arteries, it differs throughout the body and is controlled by the contraction of the heart and can vary from person to person based upon their age, weight, and overall health. The two types of pressure are referred to as systolic pressure, when the ventricles contract and push blood through the body, and diastolic pressure, the ventricle fills with blood again. High blood pressure, when blood exerts a high amount of pressure because there is difficulty moving throughout the body, has proven to be an adverse health condition involving heart disease and stroke ( 2009). Dehydration demonstrates a relationship with higher blood pressure and is referred to as 'essential hypertension' (Insel et al. 2010). There is a steady rise in blood pressure that indicates a shortening supply of water and the blood vessels react accordingly. Lumen or the tiny holes in the blood vessels are able to adapt, open and close, in response to the amount of blood. Studies have shown that only 8% of the insufficient water intake affects the volume of blood directly compared to the 66% imposed on the volume water in certain cells (Batmanghelidj 2003). However, the circulatory system shrinks by closing the lumen throughout the blood vessels. First, in the peripheral capillaries and eventually the larger vessels constrict in order to try and maintain full blood vessels. This gives a rise to tension or pressure throughout the blood vessels and a higher blood pressure overall (Batmanghelidj 2003).

There are other studies that show the importance of water balance and the key role of the antidiuretic hormone (ADH) (Purves et al. 2006). Water is such an essential part of the human body that there are specialized cells in the brain that detect the elevated sodium levels within the body and signal the pituitary gland to release ADH to indicate to the kidney that it should conserve water (Insel et al. 2010). This conserves blood volume and maintains blood pressure. When there are low levels of ADH not as much water is absorbed and dilute urine is produced. Water retention and intake dilutes the blood and expands blood volume. (Purves et al. 2006)

My experiment is to test the rapid consumption of water and the effects on blood pressure. My hypothesis is that the consumption of water will cause my blood pressure to drop because it will add to the fluidity of my blood and make is easier to pass through the arteries and the heart rate will drop because of the less pressure. The null hypothesis would be that the consumption of water would take no effect on blood pressure or cause a rise in blood pressure and heart rate. As the previous background information has shown, hydration can play a major role in high blood pressure and therefore adverse health.

Materials and Methods:

The first instrument to note would be the sphygmomanometer, a device used to measure blood pressure. Before we drank the water we had to place the sphygmomanometer on correctly and take our basal blood pressure. We had all been in a resting position for around 2 hours, this qualified as enough time to take our initial basal blood pressures. To obtain accurate results the sphygmomanometer must be placed correctly over the brachial artery and pumped to around 150 mm Hg. The average of class was obtained by adding up all the systolic pressures and dividing by 26, the number of students conducting the test and the same was performed for the diastolic pressures. The first average basal blood pressure for the class was 104/70, the second 110/71 and the third was 107/70. The sphygmomanometer also displays the heart rate of the person using it. The class's average basal heart rates were 77, 79 and 78 (beats per minute). Once the initial readings were complete the water was prepared to be consumed. The temperature of the water varied because there were students that had water bottles sitting out a room temperature for at least 2 hours while others had to fill them from the water fountain, which is chilled. Usually using a nalgene, 24 fl. oz of water were prepared to be consumed.

It can be assumed that most people in the classroom were slightly, if not significantly dehydrated because we had not drunk any water for at least 2 hours. The sphygmomanometer was prepared as before on the first partner, the water was rapidly consumed and the blood pressure and pulse was taken immediately after they were finished drinking. There was a 3 minute break between the next blood pressure reading so the other partner has the sphygmomanometer placed on their brachial artery and consumes the same amount of water and has their blood pressure and pulse was taken. The sphygmomanometer was traded between the two partners every three minutes to record the different blood pressures and pulse for the next 12 minutes. The average blood pressures for the corresponding 3 minute intervals were 120/79, 114/68, 111/71, 117/77, and 114/72. The average heart rates were 71, 70, 69, 71, and 71 likewise.

The independent variable was the amount of water consumed while the dependent variable was the blood pressure and pulse because it was what we were testing for. The constants for this experiment were time, the environment we were all in and the fact that water was consumed. This experiment was also paired because the same group of people that performed the basal readings conducted the rest of the experiment as well. There were 13 groups of two throughout the class and the same experiment was replicated in each pair.


Figure 1:

Range of Basal Heart Rate

60 bpm

Range of 0 min Heart Rate

75 bpm

Range of 3 min Heart Rate

54 bpm

Range of 6 min Heart Rate

54 bpm

Range of 9 min Heart Rate

76 bpm

Range of 12 min Heart Rate

58 bpm

Table 1

Data Range:

Figure 2:

Range of Diastolic Data:

Range of Systolic Data:

Range of Basal Systolic

68 mm Hg

Range of 0 min Systolic

84 mm Hg

Range of 3 min Systolic

59 mm Hg

Range of 6 min Systolic

53 mm Hg

Range of 9 min Systolic

62 mm Hg

Range of 12 min Systolic

49 mm Hg

Range of Basal Diastolic

58 mm Hg

Range of 0 min Diastolic

79 mm Hg

Range of 3 min Diastolic

60 mm Hg

Range of 6 min Diastolic

52 mm Hg

Range of 9 min Diastolic

77 mm Hg

Range of 12 min Diastolic

52 mm Hg

Table 2 Table 3

T-Test with Averages:

Table 4


This experiment tested the results of rapidly drinking water when dehydrated on heart rate and blood pressure of subject. The results for the average heart rate seem to demonstrate that the pulse does not change very much with the consumption of water. As for the systolic and diastolic pressures, there are some changes after the water is consumed. There appears to be a spike in the systolic pressure around the 0 minute mark and then it decreases to about average again. The diastolic pressure is much more similar to the heart rate because it is relatively consistent to the average, no drastic changes. The t-test is much more than .05 and shows that the chance these results were random is very high. The ranges of each data set display the differences between each array of data.


My hypothesis states: that the consumption of water will cause the blood pressure and heart rate to drop. My prediction is that the water will add to the fluidity of my blood and make it easier to travel through the arteries and relieve pressure. My results did not support my hypothesis because there was an initial rise in systolic pressure after the water was consumed. The pressure never dropped significantly below the basal readings and therefore my hypothesis was not supported and the null hypothesis tested correctly. If you look at the t-test table (table 4) the p-values were very high, much higher than .05, and this shows that the results had a very high chance of being random. My new hypothesis would be the consumption of water will cause my blood pressure to rise. The reasoning behind this thought is that the water adds to the mass of blood flowing throughout the body and therefore, creates more pressure on the walls of the arteries and yields a higher pressure than before. Once the water is evened out throughout the body the pressure decreases to around the basal readings.

One of the most obvious errors about this lab was the gathering of information from the class. Time is always a constraint on lab work and we ran out of time before we could gather all our information together right after the experiment. Instead, our TA had to collect all the data and put it on a spread sheet. I believe there may have been some communication issues because there are parts of the data that are considered instrumental error and there are no numbers for calculations. The other error that I noticed was the temperature of the water because we didn't actually see if everybody's water was the same temperature or not. On that note, the amount of water also varied at times because not everybody was able to measure out 24 fl. Oz with a nalgene and had to estimate.

Looking at previously published work there is evidence that dehydration and hypotension (low-blood pressure) seem to go hand in hand (Weed 1999). Therefore, when hydrated the blood pressure will rise. This is the exact opposite of what I stated in my hypothesis because I thought that addition of water would lower the blood pressure. Heart rate is also low during dehydration but is more variable if it will change during re-hydration or not (Montain and Coyle 1992). Once again, this is the exact opposite of what I predicted in my hypothesis. It appears that most previously printed work does not support my hypothesis.

As I mentioned earlier the largest weaknesses I noticed in this experiment were time, communication between TA and student, volume and temperature of water. I would suggest that more time is set aside for the collection and processing of data stage in the experiment so that the entire class is able to get the full amount of information there instead of having the TA email everybody for their results and then making a spreadsheet. The experiment can also be better prepared with pre-measured cups of water with thermometers so the temperature and volume can be more consistent.

My conclusion to this experiment is that dehydration does have an effect on blood pressure, it causes it to rise. The water adds to the pressure against the walls of the arteries. There appears to be no direct effect on the actual heart rate after the water is consumed.

Literature Cited:

Batmanghelidj, F. 2003. Water: For Health, for Healing, for Life You're Not Sick, You're Thirsty!

New York: Warner Books. p 93-100.

"Health information- water alleviate symptoms High blood pressure /Cholesterol." Drinking Water Filters- Reverse Osmosis Water Purifiers & Water Softeners. Web. 01 Feb. 2010. <>.

Insel et al. 2010. Discovering Nutrition. London: Jones and Bartlett International. p. 400-403

Purves et al. 2003. Life The Science of Biology. 7th Edition. New York: Sinauer Associates and W. H. Freeman. p. 216-221

Montain SJ, Coyle FH. 1992. Influence of graded dehydration on hyperthermia and cardiovascular

drift during exercise. Journal of Applied Physiology

Weed L, Weed L. 1999. Changing the Doctor-Patient Relationship. BMJ

Weedman D, Sokoloski E. 2009. Biology of Organisms: Laboratory Manuel. Ohio: Cengage Learning.

P. 170-183