CSB #8: BMI and its Effect on Heart Rate, Blood Pressure, and Respiration Rate

Authors: Justin Lee, Andrew Jin, and Andrew Zhang


What is a “BMI”? Literally, it means a person’s Body Mass Index, but it is often considered as a comparing measure such as weight. If a person’s BMI is under 18.5, that person is considered underweight. Normal weight is between 18.5 and 24.9, and overweight is is a BMI of 25-29.9. Beyond that, obesity is a BMI of 30 or higher.The components used in order to calculate one’s BMI are the person’s weight and height. Our group’s experiment tests whether one’s BMI affects the increase or decrease in blood pressure, heart rate, and respiration rate after exercise. We predicted that a higher body mass index will result in a higher blood pressure, heart rate, and respiration rate after exercise because the heart will have to work harder to circulate the extra oxygen needed from the extra work load. Because of this heavy work load on the heart, we also wanted to see whether there was a possible correlation between higher BMI’s and probability of heart disease. In the heart attack video we saw in class, the victim was unfit from a poor diet, and experienced a heart attack after exercising beyond his heart’s capability. The independent variables are the BMI’s of the test subjects, and the dependent variables are the change in blood pressure, heart rate, and respiration rate after exercise. We measured these using the Vernier blood pressure and vernier respiration monitor.

In our experiment, we used the Vernier Lab Pro to connect a Vernier Blood Pressure Sensor and a Vernier Respiration Monitor into a laptop. We took four test subjects of different body mass indexes, and took a control for each, measuring their normal heart rate, blood pressure, and respiration rate. We had each subject sprint for 30 seconds, and measured their heart rate, blood pressure, and respiration rate immediately after. For example, subject #1 had a BMI of 21.5 had a 117/62 mmHg blood pressure, a 114 bpm heart rate, and breathed 10.54 breaths per minute. After exercise, the subject’s blood pressure increased to 134/70 mmHg, heart rate increased to 157 bpm, and respiration rate increased to 23.36 breaths per minute. After recording the data for all four subjects, we ran statistics on the increases or decreases from normal blood pressure, heart rate, and respiration rate to the numbers after exercise. We analyzed the data in three different ways for the best expression of the results. We first made a graph comparing BMI with a ratio of the results. The ratio was made by dividing the after exercise number with the before exercise number. For example, subject #1’s ratio in heart rate would be 157/114 which is 1.38, and we compared that with his BMI. The second way we analyzed the data was by comparing the BMI with the difference between the after exercise number and the before exercise number. The last way we analyzed the data was by comparing the BMI with the percent change in blood pressure, heart rate, and respiration rate. As seen in the graph below of BMI vs. ratio of change in blood pressure, there is a clear trend. The subjects with a higher BMI had an bigger increase in systolic, but a smaller increase in diastolic. The clear trend is shown when we calculated the correlation. The graph for systolic blood pressure had a correlation of 0.890, while the graph for diastolic blood pressure had a correlation of -0.726, all figures very close to an absolute value of 1.

Our project provides further insight into the circulatory system. Although the blood pressure, heart rate, and respiration rate increased after exercise as expected, we incorrectly predicted the effects of BMI on heart rate and blood pressure. If a person has high muscle mass compared to body size, BMI will increase. Therefore, the ratio of change for heart rate should be less because the heart and muscles are strong enough to pump the blood all across the body. Also, we were correct in believing both systolic and diastolic pressure would both increase after exercise. However, a larger BMI will cause systolic to increase at a higher rate and cause diastolic to increase at a lesser rate. This phenomenon can be explained by looking at the effects of exercise on the circulatory system. When a person undergoes exercise (in our case, sprinting) their body needs extra oxygen to be able to produce enough ATP to sustain the heightened level of energy usage. Therefore, blood is pumped faster through blood vessels, increasing systolic blood pressure. On the other hand. On the other hand, when systolic pressure increases, the blood vessels are temporarily stretched, allowing the blood to flow more freely through and decreasing diastolic pressure. The stronger the heart, the more drastic the change in systolic and diastolic pressure.

CSB #7: Tilapia, Feeding the Thousands (Literally)

Source: Tilapia Farm, The New York Times

(above) A tilapia farm at work in Lake Yojoa

Scholars surmise that the fish that Jesus used to feed the 5,000 would have been Tilapia. However, in modern times today, Tilapia fish are hauled out of cages teeming with the fish in Lake Yojoa. They are then converted into fillets in a cold slaughterhouse; Some arrive in the U.S. on dinner plates within 12 hours. 


Last year, Americans ate 475 million pounds of tilapia, making it the most popular farmed fish the the U.S. It is referred to in the food industry as "aquatic chicken" for its bland taste and the fact that they are easy to breed. They are the perfect factory fish; they willingly eat pellets made of corn and soy, making them cheap to breed. Although the American Heart Association recommends eating fish twice a week, tilapia has its environmental and nutritional drawbacks. 


Tilapia fish have less beneficial omega-3 fatty acids, which are basically the reason that doctors recommend eating fish. The fatty acid combinations in farmed tilapia are less healthier than that of wild tilapia, because the farmed fish are fed corn and soy while the wild tilapia eat lake plants and algae. A vast majority of the tilapia fish consumed in the U.S. are harvested from "pens" and "cages" in Latin America and Asia. Today, environmentalists argue that unregulated fish farming methods is detrimental to ecosystems in poor countries. This is because the fish are mass farmed (overpopulated) in natural lakes, and as a result, the fish waste pollutes the water. 


However, defenders state that the Aquaculture Stewardship Council is toughening regulations to make sure tilapia farms are "responsibly farmed." They also argue that tilapia farming will only rise in importance as the population rises, and more people are fed and work jobs. “There are going to be more farmed fish each year,” said Kevin Fitzsimmons, a biologist at the University of Arizona. “Think about it: if we tried to get beef from hunting, there would be a lot of hungry people.”


However, it is this rise in importance that worries many biologists. They fear that the industry will become so important, that it will outweigh caution and destroy lake habitats and leave species extinct. Dr. McCrary has spent the past decade studying how a small, short-lived tilapia farm degraded Lake Apoyo in Nicaragua. “One small cage screwed up the entire lake — the entire lake!” he said of the farm, which existed from 1995 to 2000.

Waste from the cages polluted the ecosystem, and some tilapia escaped. An aquatic plant called charra, an important food for fish, disappeared, leaving the lake a wasteland.

I think that although it may be easy to farm, the tilapia farming industry is very risky as shown by Dr. McCrary in Lake Apoyo. Also, doctors state that salmon has ten times more omega-3 fatty acids than tilapia, giving it much less nutritional value. 

Source: 

Rosenthal, Elisabeth. "Another Side of Tilapia, the Perfect Factory Fish."
     The New York Times. New York Times, 2 May 2011. Web. 7 May 2011.
     <http://www.nytimes.com/2011/05/02/science/earth/
     02tilapia.html?pagewanted=1&_r=1&ref=earth>.