Effects Of Hydration On Blood Pressure Biology Essay


The effects of hydration on blood pressure and heart rate are very diverse and can differ from study to study. Some believe that you can prevent getting high blood pressure by constantly drinking water and staying hydrated early in life (Healthy Water). Many others believe that proper hydration allows the blood's consistency to be correct, thus allowing the body to maintain proper blood pressure during times of stress such as exercise (Nadel et al. 1980, Woods 1983). Finally, some have found that hydration can slightly increase blood pressure. This increase was found in the systolic blood pressure and was also found in older subjects (Jordan 2000). In this experiment we wanted to see for ourselves how hydration will affect blood pressure. During the test, our hypothesis is that blood pressure will decrease with hydration. We believe that when you are dehydrated your blood gets thicker causing an increase in blood pressure, thus hydration will decrease blood pressure by adding more liquid to the blood causing it to flow better. Finally, it is important to know how hydration affects blood pressure so that the population of the world can properly maintain their blood pressure.

Materials and Methods:

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In this experiment we used a sphygmomanometer, a clock and a container that can hold at least 16 oz of water. In order to perform this experiment we first had our subjects not drink any water in the morning to dehydrate them a little bit. This will allow us to see if water has any effect on blood pressure. Before drinking any water, we must take three baseline readings of our subject's blood pressure and heart rate using the sphygmomanometer. Once we have completed this we had our subject drink 16 oz of water. Immediately after they finished drinking we took a blood pressure and pulse rate reading, this would be our zero reading. We continued to take a reading every three minutes, until we reached a total time of 12 minutes. While taking measurements we noted any changes in blood pressure or heart rate that we noticed. In this experiment our dependent variables were the amount of water consumed, how dehydrated our subject was and placement of the blood pressure cuff. Our independent variables were the room temperature, sex of the subject and the age of the subject.


Hydration had little effect on both blood pressure and heart rate during our experiment. This can be seen in both figure 1 and 2. It can be seen from figure 1 that pulse rate was the only reading that actually decreased. The average pulse rate at the beginning of the experiment was 77.08 beats per minute and at the end of the experiment it was 70.56 beats per minute. This difference in pulse rate had a p-value of 0.005 making this reading significant. This means we are 95% confident our data is correct or falls in a correct range of values for our stats. The systolic blood pressure at the beginning of the experiment was 112.12 mm/Hg, and 113.6 mm/Hg at the end. The reading for systolic blood pressure had a p-value of 0.696 making it not significant. Finally, the reading for diastolic blood pressure was 70.19 and 72.12 at the beginning and the end respectfully.

Figure 1

Above is a bar graph showing the results of the experiment. The stats for this chart are in mm/Hg.

Figure 2

Above is a graph showing the chances in all three stats during the whole experiment. The Blue and Red lines are in mm/Hg and the green line is in beats/min.

Figure 3 Statistics


3 min

6 min

9 min

12 min

Pulse Rate
























Hydration did not have a significant effect on blood pressure but it did have a significant effect on the pulse rate. These results both support and do not support our hypothesis. Hydration did not cause blood pressure to drop like we had predicted, it actually caused blood pressure to increase from 112.12 mm/Hg to 113.6 mm/Hg. Our experiment was not a total failure because it showed a significant decrease in pulse rate from 77.08 to 70.56.

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Our experiment may not have shown us what we expected due to many reasons. We could have encountered errors while taking blood pressure, such as incorrect placement of the cuff. In our experiment our subjects may not have been adequately dehydrated for us to see any noticeable changes in blood pressure. An increase in time and/or water consumed may give us better results for blood pressure. As far as pulse rate goes we saw exactly what we expected to see with a decrease in seven beats by the end of our experiment.

Compared to other experiments our results showed some differences. In a high blood pressure remedy website they found that one of the big causes of high blood pressure was dehydration, and as a remedy they believe that proper hydration will not completely rid you of high blood pressure but it will help you lower or keep your blood pressure low (Healthy Water). This was the total opposite of what we found in our data. Our experiment was not alone in finding that drinking water increases blood pressure though. In an article put out by the American Heart association about circulation, they found that "systolic blood pressure increased profoundly with water drinking" (Jordan 2000). Along with that finding they also found that this effect can be seen more in older patients. Although I believe our experiment was fairly accurate, I would like to redo our experiment with the corrections mentioned above to see if those corrections would change our results. I also would like to redo our experiment to get a definite answer to whether hydration increases or decreases blood pressure since our data said it increases blood pressure but I found and article that stated otherwise.

After examining our experiment I believe we had many weaknesses in our set up and procedure. We were rushed for time at the end of class, which lead to many of the errors we ran into. Given another chance with more time to set up and get better readings, I feel our experiment would have shown us some more positive results. Overall, we feel like we have learned a lot from our experiment. We have learned that hydration does result in a decrease in pulse rate. Along with finding the decrease in pulse rate we also found that hydration had no effect on blood pressure.


Jordan J, Shannon JR, Black BK, Ali Y, Farley M, Costa F, Diedrich A, Robertson RM, Biaggioni I, Robertson D. 2000. The Pressor Response to Water Drinking in Humans. American heart Association, Inc.

Nadel ER, Fortney SM, Wenger CB. 1980. Effect of hydration state on circulatory and thermal regulations. The American Physiological Society.

Woods RL, Johnston CI. 1983. Contribution of vasopressin to the maintenance of blood pressure during dehydration. The American Physiological Society.

Weedman Donna, Sokoloski ES. 2009. Biology of Organisms. 5th ed. Cengage Learning. pg. 173-184.

Dehydration and high blood pressure. www.healthy-water-filters.com/dehydration-high-blood-pressure.html. 2/1/10