The Effects Of Hydration In The Circulatory System Biology Essay

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The blood pressure of an average healthy adult should have be around 135/85 mm Hg, where the numerator number is the systolic pressure (contraction of the heart) and the denominator is the diastolic pressure (relaxation of the heart). (Verdecchia P, Schillaci G). The objective for this lab is to test if hydration has an effect on blood pressure and pulse rate. The brain sends signals to the rest of the body to maintain a stable blood pressure, and when there is a lack of water of fluid volume, and then the heart must beat faster to keep a constant blood pressure. (MedicineNet©1996-2010) If the heart must beat faster when there is a deficient amount of fluid volume in the blood stream then it can be assumed that the hear rate will decrease when hydrated because there is more volume in the veins to pump around the body. (MedicineNet©1996-2010) Water is absorbed into the blood plasma and the plasma has an osmolarity (ability to uptake water) of 300milliomoles per liter (Saladin, Kenneth S. 2009). There was hardly any increase in blood pressure when 2 liters of water were consumed by a subject.( E. R. Nadel, S. M. Fortney 1980). In this lab, it is unlikely there will be any significant change in blood pressure since only 350ml were consumed in a short period of time. I hypothesize that hydration does in fact affect the blood pressure because through osmoregulation, the plasma in the blood cells should gain volume when water is taken in the cell. Also, I hypothesize that the heart rate levels will decrease the more hydrated the cells in the blood stream become because the heart will perform less work to pump blood throughout the body when the blood pressure is higher.


I filled a Nalgene water bottle up with 12 ounces (350 ml) of cold water from the common drinking fountain which acts as part of the experiment's independent variables. Then, I consumed the liquid within a 5 minute (300 second) time span. Directly after consuming the water, I measured my blood pressure and heart rate using the sphygmomanometer on my arm. I then copied the data down from the pressure gauge recording the exact blood pressure and heart rate. Next, I had to wait and relax for four test trials with three minutes (180 seconds) in between each blood pressure and heart rate recording. It is crucial to test with three minutes in between trials because time is an independent variable in this experiment. I then compared the data with the sphygmomanometer measurement of blood pressure and pulse rates before drinking 350ml of water to see if hydration is a dependant variable related to blood pressure and pulse rate. The data collect from the sphygmomanometer is depicted as heart rate (mm Hg) over time (minutes) and the systolic (mm Hg) and diastolic (mm Hg) rate differences over time. The T-test also shows if there was a relative change in heart rate and hydration.


The results shown in figure 1, 2, and 3 are correlated with each other and have the same trends. After the basal reason of the blood pressure and the heart rate, all the graphs increase in pressure or beats per minute and then decrease in the second reading at six minutes. By observing figure 2 and figure 3, the systolic and diastolic values increase and decrease in rate even though the diastolic rate is more fluctuating than the systolic rate. The T-test data was calculated to see if there was an important variation in results based on temperature. The test was taken based on cold water intake versus room temperature water intake.

Figure 1

Figure 2

Figure 3


0 min Cold vs. 0 min room temp (PR)

0.09571 No relevance

6 min cold vs. room temp BP

0.435679 No relevance

PB 0 min vs. 6 min

pvalue 0.2531 No relevance

PR 0 min vs. 9 min

pvalue 0.8377 No relevance

sys 0 min vs. 6 min

pvalue 0.0447 Related

Overall, the experiment was hard to tell in the heart rate and blood pressure was affected by hydration possibly because there was not enough water consumed to make a significant difference in the hydration of the blood plasma. As seen in the T-test data, there were no correlation between cold water or room temperature water and blood pressure. In figure 2 and 3 the blood pressure and heart rate are directly related. Observing figures 2 and 3, the lowest heart rate for both systolic and diastolic occur at about 6 minutes. I hypothesized that the blood pressure would increase due to the added volume of water that would osmoregulate inside the cell plasma and that the heart rate would decrease because there heart would not have to pump as much blood through the body due to the increase in blood pressure. Through the results in my experiment, the hypothesis that the blood pressure would increase was not supported. In fact, the blood pressure decreased and then increase slightly after the initial test at three minutes. Compared to other lab results from previous experiments, the data show no difference in blood pressure from over-hydrated subjects and regular subjects (Koosmans 1986). An alternative experiment that I could have performed to shore more adequate and precise results might be if the subject consumed more water of at least 0.9 liters more in a set period of time. If there was at least 0.9 liters more water ingested this amount would have a considerable volume increase to see a change in blood pressure. I would still keep my original hypothesis that the blood pressure would increase with hydration but I would still be skeptical with the results since previous experiments had no evidence that hydration is correlated to blood pressure through scientific evidence. The biggest weakness that occurred in this lab vary from not having a set pulse rate for every student to participate in this experiment, because everyone's blood pressure and heart rates are different, it is difficult to have a strong basal reading. Secondly, it is difficult to tell if the heart rate and pulse rate are fluctuating randomly during the times we calculated rates. The T-test helps on a small scale to display what information is relevant to the lab.

From this experiment, it is still questionable as to whether hydration affects pulse rate and blood pressure because of the errors in this lab. For example, students did not intake the same about of water for the test and not having an exact beginning heart rate for all of the students participating in this lab.


©1996-2010 MedicineNet, Inc, Dehydration (cont.) Dehydration (Internet)

(Cited February 1, 2010. Available from

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E. R. Nadel, S. M. Fortney, and C. B. Wenger, Colorado State University 1999

Effect of hydration state of circulatory and thermal regulations

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