Blood pressure and heart rate in humans



Blood pressure is the measurement of arterial pressure as a result of the contraction and relaxation of the heart. The pressure upon the contraction of the heart is normally defined as the systolic pressure while the pressure upon relaxation is referred to as the diastolic pressure. Both are measured in milliliters of mercury (mm Hg) and are most important in measuring a healthy blood pressure. The heart rate, which is usually expressed in beats per minute, is also important when measuring the strength and wellness of a heart.

An individual with a healthy heart will usually have a systolic pressure of 120 mmHg and a diastolic pressure of 80 mmHg (Bishop 2009). A normal heart rate is within the range of 60 bpm and 80 bpm (Weedman 2009). The most common way to measure an individuals blood pressure and heart rate is with a sphygmomanometer, a machine that when used correctly is able to accurately determine a person's blood pressure.

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Both blood pressure and heart rate are unfixed and constantly changing in response to the body. Factors such as diet, exercise and physical and psychological stress can alter the arterial pressure. An individual's blood pressure will increase when the vessels in the body constrict while the heart tries to continually pump the same amount of blood throughout the body. The blood pressure will decrease when the vessels increase in diameter and blood is able to flow through them with ease. High blood pressure is referred to as hypertension while low blood pressure is referred to as hypotension. An individual's body might react to pain or stress with an increase in blood pressure or respond to constant and frequent exercise with an over all decrease in blood pressure over a period of time.

Hydration is an important part of the circulatory system. Appropriate hydration is crucial for normal body function. Hydration helps to distribute the necessary nutrients, regulate body temperature and dispose of waste within the body (Patterson, 2005). Water should make up approximately 60% of an adults body weight. A lack of proper hydration can affect blood volume, plasma volume and the volume of red blood cells in the body (Costill 1974).

In the experiment we designed and performed in class, we wanted to observe different factors affecting blood pressure. We asked the question, “Does hydration effect an individuals blood pressure and heart rate?” We then generated a testable hypothesis that the consumption of water will increase blood pressure as well as heart rate.

Materials and Methods:

We began the experiment by choosing two variables, dependant and independent. The independent variable was ingestion of 16 ounces of water in order to hydrate an individual; the dependant variable was the measured heart rate and blood pressure. We also designated our experimental replicates groups. All together there were a total of 26 individuals in the experimental group. The entire experimental group was divided into pairs. When blood pressure and heart rate were taken throughout the experiment, they were taken by the individual's partner. We took three basal / resting blood pressure readings. To do so we placed the blood pressure cuff on the left arm of the individual tested and used the sphygmomanometer to determine the individual's resting systolic and diastolic blood pressure as well as his/her heart rate. To correctly situate the pressure cuff on the arm, we assured that the cuff was placed approximately 3 cm above the elbow. We made sure there was no bulky clothing between the individual's arm and the cuff. The tube leading from the sphygmomanometer to the cuff was situated on the innermost side of the arm, near the brachial artery (Weedman 2009). When wrapping the pressure cuff around the arm, we assured that it was neither too snug or to loose. We pumped the cuff with the rubber bulb until it reached 150 mm Hg. To do so required that we squeeze the bulb while our finger covered the air hole and releasing to allow the bulb to refill. Once at 150mm Hg, the sphygmomanometer gradually released the pressure until the digital reading came up on the screen. We then recorded the data and repeated this step two more times to have a total of three basal readings.

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After retrieving the resting blood pressure, we had the individual consume about two cups (16 oz) of water quickly (less than one minute) and the partner immediately took a blood pressure reading with the sphygmomanometer. We followed the initial post reading with four more readings in time intervals of three minutes switching off between partners. We recorded the systolic, diastolic, and heart rate for each of these readings. The cuff was taken off after each reading to allow the pressure to be reestablished in the individual between each reading.

Throughout the experiment, the data was collected by each individual and then collected and put into an excel spreadsheet. The data that was collected included each subject's basal and experimental blood pressure and heart rate readings along with the relative temperature of the water consumed (cold or room temperature). The collected data was then analyzed using different forms of statistics. We used a “T test” as well as dividing relevant data into subgroups and found the range and average of the data.


In this experiment, we exposed a group of 26 individuals to dehydration and then had them consume a total of 16 ounces to rehydrate. Their blood pressure was then taken immediately as well as in intervals of three minutes for a total of twelve minutes. We predicted that hydrating an individual would increase their blood pressure and decrease the heart rate, however, we found that hydration in fact does the opposite.

When organizing and reviewing the data for this experiment it is clear that our results for this experiment were relevant. Our data was calculated based on averages of pulse rates and blood pressures. Our averaged data was then organized in graphs and tables that were divided into subgroups based on the temperature of the water consumed (cold, room temperature, and unknown temperature). Finally, the ranges of each subgroup and T-tests were calculated based off of our data. We calculated three T-tests from our data. One T-test used results of average pulse rate readings from the cold, room temperature, and unknown water consumed. Another T-test was calculated from the average systolic results from the cold water, room temperature water, and the unknown water consumed. The final T-test used the average diastolic results from the cold water, room temperature water, and unknown water consumed. The values for each T-test can be seen in Tables 1, 2, and 3, T-tests. Because the values for each of the T-test was less than 5%, it can be concluded that the data collected shows a correlation between hydration and blood pressure and heart rate.

In graph 1, the room temperature graph, the heart rate overall decreased. In graph #2, the second room temperature graph, the systolic and diastolic pressures also decreased. In the cold water heart rate graph, graph #3, the heart rate drastically increased. In graph #4, both the systolic and diastolic pressures decreased. Finally, in graph #3, the graph showing unknown temperatures of the water, the heart rate had an overall decrease. Graph #4 showed that the diastolic pressure had an overall decrease in pressure while the systolic had an overall slight increase.


Originally, we hypothesized that blood pressure and heart rate would be affected by hydration. We predicted that an increase in hydration would proportionally increase the blood pressure and heart rate. Our results do to some extent support our hypothesis and predictions. Our results show that hydration does affect blood pressure and heart rate. Our data collected generally shows that hydration, over a short period of time, will overall decrease the arterial pressures (systolic and diastolic) as seen in Graphs 2, 4, and 6. The data in each subgroup also shows that pulse rate will be affected differently by different temperatures of water. When ingesting cold water, the pulse rate generally increases, while those that consumed room temperature water have a decreased pulse rate as seen in Graph 1 and 3.

A hypothesis that would correctly support the results of this experiment would be, “Hydration (the consumption of water) will decrease blood pressure while cold water will increase heart rate.” Though this hypothesis is accurately supported by the results, this hypothesis may also be incorrect. One way it can be determined that our results wholly support our hypothesis is the value of the T-tests calculated for this experiment. The value of the T-tests based off of the average pulse rate, systolic pressure, and diastolic pressure were all below 5%. This shows low variability within the experiment and suggests that our experimental results are valid. Because the T-test was below 5%, it can be concluded that our results from this experiment are significant.

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Our results support the fact that hydration does decrease blood pressure. After much research, it is shown that, “dehydration and blood pressure are linked - that it is not aging that leads to High Blood Pressure, but rather dehydration.” (Healthy Water 2007). Our results for our experiment relate to this statement because our data shows that hydration lowers blood pressure, and inversely suggests that dehydration would do the opposite by increasing blood pressure. When an individual is dehydrated, their blood vessels compensate the lack of water by contracting and heightening blood pressure. When an individual is sufficiently hydrated their vessels are filled with a high blood volume that holds the vessels open and relaxed while transporting water to fundamental organs and systems throughout the body.

There were many weaknesses and flaws in our experiment and experimental design. One flaw in experimental design was the lack of a control group. Though basal readings were taken prior to the experiment, there was no separate group that was not treated with the independent variable and measured throughout the experiment. Also, our experiment was done in a hurry that could have affected the blood pressure and heart rate throughout the experiment. The sphygmomanometers that were used often came up with “error” which may have contributed to the insignificance of our data. Finally, there was no way of measuring the level of dehydration of the experimental group prior to drinking the 16 ounces of water. The data will vary with the different levels of hydration and without knowing the exact level of hydration of each individual it would be impossible to group them together.

Though our results did not match our hypothesis, they were comparable to similar experiments. Our data did show that an increase in hydration will decrease blood pressure. However, our data and experimental design is neither accurate or acceptable due to errors in experimental design and experimental flaws.

Literature Cited:

Bishop T. 2009.Measuring Blood Pressure. Practice Nurse 38: 11-16.

Costill DL, Dill DB. 1974. Calculation of percentage changes in volumes of blood, plasma, and red cells in dehydration. Journal of Applied Physiology 37: 247-248.

Healthy Water. 2007. Dehydration and Blood Pressure disorders are linked. February 20, 2009.

Patterson SM, Rochette LM. 2005. Hydration status and cardiovascular function: effects of hydration enhancement on cardiovascular function at rest and during psychological stress. International Journal of Psychophysiology 56: 81-91.

Weedman D, Sokoloski ES. 2009. Biology of Organisms. 5th Edition. Mason, OH: Cengage Learning. P 173-184.