Introduction

Body mass and blood pressure have been linked closely over the years. The issue of obesity - “globesity” - and hypertension is becoming more and more prevalent in today’s society. Obesity increases the strain on the heart and also increases blood pressure which can eventually lead to heart diseases. Heart diseases account for many of the deaths in Singapore every year; it accounts for almost 23% of deaths. Recognising risk factors for heart diseases early estimates the susceptibility to coronary heart disease.

In this study, we intend to generate relevant information that helps to understand the pattern between an individual’s blood pressure and body mass. Such information would highlight the chances an individual would get heart diseases in the future and thus be relevant to the prevention and control of heart diseases.

Hypothesis: Is there a relationship between Body Mass Index (BMI) and Blood Pressure?

Literature Review

BODY MASS INDEX (BMI)

Being overweight or obese increases the risk of having high blood pressure and increases the risk of cardiovascular disease associated with hypertension. The definition of overweight and obese are based upon a calculation called Body Mass Index (BMI).

Body Mass Index (BMI) is a number calculated from a person's weight and height. BMI is a fairly reliable indicator of body fatness for most people. BMI does not measure body fat directly, but research has shown that BMI correlates to direct measures of body fat, such as underwater weighing and dual energy x-ray absorptiometry (DXA).

BMI is an inexpensive and easy-to-perform method when compared to skinfold thickness measurements (with calipers), underwater weighing, bioelectrical impedance, dual-energy x-ray absorptiometry (DXA), and isotope dilution where these methods are not always readily available, and they are either expensive or need highly trained personnel. Furthermore, many of these methods can be difficult to standardize across observers or machines, complicating comparisons across studies and time periods.

A person is said to be overweight if their BMI is greater than 25, while a person with a BMI greater than 30 is said to be obese. Obesity raises blood pressure and makes high blood pressure more difficult to control.

Formula:

The formula for BMI is weight (in kilograms) divided by height (in metres) squared.

Example: Weight = 68 kg, Height = 1.65 m

Calculation: BMI = 68 ÷ (1.65)² = 24.98

For adults 20 years old and older, BMI is interpreted using standard weight status categories that are the same for all ages and for both men and women. The standard weight status categories associated with BMI ranges for adults are shown in the following table.

BLOOD PRESSURE

Blood pressure is the pressure of the blood against the walls of the arteries. To determine one’s blood pressure, doctor measures the maximum pressure (systolic) and the lowest pressure (diastolic) made by the beating of the heart.

The systolic pressure is the maximum pressure in an artery at the moment when the heart is beating and pumping blood through the body. The diastolic pressure is the lowest pressure in an artery in the moments between beats when the heart is resting.

The systolic pressure is always stated first. For example: 120/80 (120 over 80); systolic = 120, diastolic = 80.

Both the systolic and diastolic pressure measurements are important - if either one is raised, it means you have high blood pressure (hypertension).

The blood pressure in our body is always changing and it is part of the human physiology. It is very rare that someone's blood pressure is always the same because we are always active and we are always doing different things like eating, sitting, standing, walking, breathing, moving around and doing so many other things throughout a day.

Every time that we do something different, our blood pressure changes and it react to the different positions that we are in. It is important that doctors and other professionals have the set rate for each person that relates to blood pressure and what it should be, because it is just impossible for anyone to take his or her blood pressure all the time throughout the day.

This is why mean arterial pressure is important. Mean arterial pressure is a term used in medicine to describe a notional average blood pressure in an individual. It is defined as the average arterial pressure during a single cardiac cycle. Therefore, MAP is a useful medical measurement that indicates both overall health and risk for developing various cardiovascular diseases such as hypertension.

MAP is calculated based on the formula as shown below:

SBP: Systolic Blood Pressure
DBP: Diastolic Blood Pressure

Normal values of MAP vary widely but usually range between 77-97 mmHg.

Methodology

Equipment used for measuring:

Height:
Measuring Tape and Ruler


Weight:
Bathroom Scale


Blood Pressure:
Sphygmomanometer and Stethoscope


A sample size of 30 was randomly chosen from our class.

They were briefed to refrain from eating or drinking, smoking and taking medications that can affect blood pressure at least 1 hour prior to taking measurement.

The blood pressure readings were taken first prior to the height and weight measurements.

Measurements Taken and Calculations Derived

Blood Pressure:

Blood pressure is measured using a sphygmomanometer. Blood pressure is not the same all over the body and the most accurate way to measure blood pressure is to use an artery closest to the heart, that is, brachial artery blood pressure. This can be measured from above the subject’s elbow. Furthermore, it is convenient and ensures consistency.

After obtaining verbal consent, the subject sits down and rests their arm on a table so the brachial artery is level with the heart. This is important when monitoring blood pressure, as pressure is proportional to height (Δp = ρgΔh).



A sphygmomanometer cuff is wrapped around the subject's upper arm, just above the elbow, with the air tube on the same side of the palm facing up. Place the air tube in line with your middle finger and a stethoscope is placed on the hollow of the elbow.
The cuff is 'pumped-up' to a pressure of 180mmHg, compressing the brachial artery hence causing the artery to collapse once the systolic pressure has been exceeded. At the point where the pressure of the cuff is greater than the systolic pressure, the artery has collapsed thus, there is no flow of blood through the brachial artery.

The valve on the pump is loosened slowly to allow the pressure of the sphygmomanometer cuff to decrease. Once the systolic pressure is reached (approximately 120mmHg in the 'normal' case), the brachial artery opens causing volatile blood flow, which cause vibrations against the artery walls. These noises (called Korotkoff sounds) can be heard through a stethoscope as the pressure exerted onto the brachial artery falls. The blood flow through the brachial artery increases steadily, until the pressure of the sphygmomanometer cuff falls below the diastolic pressure, approximately 80mmHg.


Weight:


The subjects were told to remove their footwear as well as empty their pockets. Body weight was measured (to the nearest 0.5 kg) with the subjects standing motionless on the bathroom weighing scale.


Height:


The subjects were told to remove their footwear. Height was measured (to the nearest 0.5 cm) with the subjects standing in an erect position against a wall that has a measuring tape attached to it. The subjects' heads were positioned so that the top of the external auditory meatus was level with the inferior margin of the bony orbit. A ruler was used to avoid parallax error when taking the readings.


To ensure the accuracy of the height and weight measurements, we took 3 readings for the measurement of each subject. The mean values of weight and height was tabulated and recorded using SPSS.


Body Mass Index (BMI):

BMI was then calculated using the formula:

Mean weight and height was used to calculate BMI for accurate representation.


Mean Arterial Pressure (MAP):

MAP is calculated based on the formula as shown below:

SBP: Systolic Blood Pressure
DBP: Diastolic Blood Pressure
Diastolic and systolic pressure is obtained from the sphygmomanometer readings.

Statistical Analysis and Results

Raw Data:



Null Hypothesis, H₀:
There is no significant relationship between Body Mass Index (BMI) and Blood Pressure.

Research Hypothesis, H₁:
There is a relationship between Body Mass Index (BMI) and Blood Pressure.


Variables:



Appropriate statistical technique:
The proposed test is Pearson’s R technique.
The scatter appears to follow a general linear positive linear trend. There is no violation of the linearity assumption.



Results:



Final statement:
Since the significant level, p= 0.079 is more than 0.05, we fail to reject H₀ and conclude that there is no significant relationship between BMI and Blood Pressure.

Conclusion

From our literature review, it can be seen that there is a supposedly related association between BMI and Blood Pressure. However, our results have shown otherwise. This could be due to the fact that the number of respondents is small (n=30), and also that most of our respondents are relatively young and healthy (aged 19-25). Moreover, no account was taken to find out the activities which the respondents went through prior to the measurements of their blood pressures. Such activities include the consumption of caffeine-containing beverages such as tea and coffee, and vigorous exercises. These factors could raise a person’s blood pressure and thus, could have affected our statistical results.

Reflections

Shiela Farziana

We had difficulties getting started on this project as most of the parameters such as weight and height were of sensitive context. But once we had that settled, we worked together as a team to get the task at hand done. As with all group work, we did encounter certain disagreements yet we managed to overcome them and carry on with our project efficiently. Through this project, I learnt the benefits of using statistics and will definitely implement it in my future research and projects. I had fun carrying out all those measurements and overall, had a fruitful experience. =P


Rina Dashim Shah

This whole experience has been an enriching one. As a group, we tried, learned and used SPSS and discovered many of its functions which aided us in our hypothesis testing. Learning and experiencing this would not only be beneficial in my education but also in the future when I enter the real world.


Chan Weisiang Jason

From this project, I’ve learnt that the collection of data requires a lot of manpower, time and most importantly patience. It is a tiring process and it doesn’t help that some respondents get a little cranky as they find that revealing their weight or height is a tad too sensitive. This project also teaches me to let the results do the talking even though our hypothesis may not be supported by the results.


Lee Haoming Kenneth

This project has taught me that in whatever we do, it is very important to start off on the right foot. Setting clear objectives would make it easier to know direction in which we're heading. In this case, setting the right hypothesis was the first step. Even then, what happens in reality might not be what we expected theoretically, as demonstrated when our statistical findings were not in accordance with our expectations based on our literature review. We just have to learn to take things as they come and go with the flow, and strive on till the end.
Learning to use SPSS was not easy, but the applications of SPSS are undeniably vast. The knowledge of SPSS is definitely useful to have.
On the whole, it was an enriching experience, and I hope that we managed to spread the "Healthy Lifestyle" message through this project.


Tay Yi Xiang

I had an enjoyable experience doing this project while learning a lot from it. Stats can be fun and useful when conducting meaningful research. A lot of hard work was put into this project by all the group members who had to analyze the data collected and also research on the topic. We hope that by reading this blog, you will be able to appreciate statistics and learn more about BMI and Blood Pressure.


Sim Wei Yow

Besides knowing more in dept about the topic our group had researched on. I’ve learned that coming out with a simple hypothesis isn’t a simple task at all! Accuracy in the collection of the data is very essential. Although we faced problems at the initial phase but we found our way after seeking advice from professionals in the field. I’ve also learnt to work in a team better and more efficiently. I hope that through this statistics project, we could achieve our objectives and the findings could be useful to anyone who had read it. Thank you.

Acknowledgements

We would like to thank Dr Muyar, Dr Anna, and Dr Maw for providing us with professional advice, as well as the Sphygmomanometers and Stethoscopes, without which this study would not have been possible.

We would also like to thank our kind respondents for volunteering to be part of this study.