ay Abstract
The literature on cardiovascular physiology reports that exercise leads to a large increase in the body’s intake of oxygen which has a serious effect on the circulatory system (Shepard, 1999; Laughlin, 1999). During our investigation, we examined how exercise affects various cardiovascular variables, including pulse rate, systolic and diastolic blood pressure, the P-T interval, the T-P interval, and pulse lag. In order to explore this problem, we compared these cardiovascular variables for two treatments. We designated treatment one to be the cardiovascular variables measured before exercise and we designated treatment two to be after exercise. The exercise we chose to perform was thirty jumping jacks. Based on the results measured before and after exercise, we were able to conclude only the P-T interval is significantly different between treatment one, before exercise, and treatment two, after exercise. This undermined our initial prediction prior to the experiment that each of the variables would be significantly different between treatments. We were able to infer, based on the results, that pulse rate, blood pressure, the T-P interval, and pulse lag are not dependent on moderate exercise.
Introduction
The cardiovascular physiology experiment served the purpose to determine whether a moderate exercise was a factor that would influence the pulse rate, systolic blood pressure, diastolic blood pressure, P-T interval, T-P interval, and pulse lag of several subjects when tested subjects performed thirty jumping jacks. According to Shepard (1999), vigorous exercise makes some significant demands on our body’s ability to maintain homeostasis. This is due to the increased consumption of oxygen during exercise. When muscles are active during exercise, they are low in oxygen, so the heart has to pump faster to supply oxygenated blood to the muscles. The increase blood flow leads to an increase in pulse rate, or heart rate. Heart rate is the amount of time the heart beats per minute. For females, the average resting heart rate is 72-80 bpm, and for males, the average heart rate is 64-72 bpm. Heart rate tends to be slower at rest for those who are more physically fit (Marieb, 1989). Consequently, individuals with higher heart rates at rest are at higher risk of developing cardiovascular problems which can lead to death. We would anticipate faster flow of blood in major arteries during exercise; therefore, faster beats per minute.
Systolic blood pressure is the pressure of blood in the vessels of the heart when the heart beats. Diastolic blood pressure is the pressure during rest. Marieb (1989) proposed that systolic blood pressure during rest in adults is between 110 mmHg and 140 mmHg and diastolic from 70 mmHg to 80 mmHg. Exercise is accompanied by stimulation of the sympathetic nervous system, which causes vasodilation of blood vessels in the active muscles and vasoconstriction of blood vessels throughout the body. Blood pressure is increased as a result. However, the type of exercise is a determining factor in how dramatic blood pressures changes. (Guyton, 1985)
The P-T interval is the time, in seconds, from the end of the P wave to the start of the T wave. This is the duration of the electrical events, the depolarization of the atria and ventricles, which occur for each beat of the heart. According to Goodman (1999), during and shortly after exercise, the P-T interval is expected to shorten. This is because the heart beats at a faster rate during exercise in order to supply the muscles with more oxygen, so more pulse peaks can be seen on an ECG. Also, these peaks would be closer together.
The resting period of the heart is known as the T-P interval on an electrocardiogram, or ECG (Goodman, 1999). It is the time, in seconds, from the end of the T wave to the start of the P wave. During and shortly after exercise, the T-P interval is expected to shorten like the P-T interval; however, if the heart beats at a fast enough pace, we would see the disappearance of the T-P interval.
Pulse lag is the amount of time it takes for a pulse of blood to reach the tip of the finger after the depolarization of a ventricle. Ultimately, the pulse lag is correlated with the P-T and T-P intervals. So, we can see than with exercise, as the P-T and T-P intervals shorten due to a faster heart rate, the pulse lag would decrease.
My explanatory hypothesis states: Exercise stimulates both the cardiovascular and respiratory systems of the body so that muscles can be supplied with more oxygen. Based on this hypothesis, we made an initial prediction. We predicted that heart rate and blood pressure would increase, the P-T interval and the T-P interval would shorten, and pulse lag would decrease due to moderate exercise. We arrived at this prediction based on the thought that exercise stimulates the sympathetic nervous system given this sympathetic release intensifies the pace of the SA node depolarization in the heart (Guyton, 1985). The research hypothesis, or alternative hypothesis, led to the development of the null hypotheses for each variable as follows. Pulse rate will be the same before and after exercise. Systolic blood pressure will be the same before and after exercise. Diastolic blood pressure will be the same before and after exercise. The P-T interval will be the same before and after exercise. The T-P interval will be the same before and after exercise. Pulse lag will be the same before and after exercise. Therefore, the research hypothesis states: The cardiovascular variables will be different before and after exercise.
Materials and Methods
The foundation of our method for the experiment included simple experimental design in addition to following the steps of the scientific method. Prior to performing the experiment, my lab section designed our experiment. We made the generalization that exercise would affect pulse rate, systolic blood pressure, diastolic blood pressure, the P-T interval, the T-P interval, and pulse lag. We decided on the problem we would be testing: cardiovascular function before and after moderate exercise. In addition, we decided what exercise we would be performing to investigate the problem. We decided to each complete thirty jumping jacks. We then formed our explanatory hypothesis and defined the variables of the experiment. Our independent variable was exercise, our dependent variables were pulse rate, systolic and diastolic blood pressures, the P-T interval and T-P interval from the electrocardiogram, and pulse lag, and our controlled variables were age of the subjects being tested and that the subjects were equally male and female. We then reflected our explanatory hypothesis in our prediction that heart rate and blood pressure would increase, the P-T interval and the T-P interval would shorten, and pulse lag would decrease due to moderate exercise. Using that prediction, we formed a research hypothesis and six null hypotheses.
The Cardiovascular Physiology OMP handout and procedures of Kosinski (2016) states the procedures to follow in order to first complete measuring blood pressure using a digital sphygmomanometer. We split up into partners and took turns taking each other’s blood pressure. First, we had our lab partners sit down and roll up their sleeves if needed. Then, we slipped the cuff of the sphygmomanometer around their upper arm and wrapped it tightly. After pressing the “Start” button on the digital monitor, the cuff automatically inflated to 170 mmHg and decreased gradually by itself. We then recorded the systolic and diastolic pressures displayed on the monitor. When finished, we turned off the monitor by pressing the “Start” button again.
The handout also states the procedures to follow in order to set up, operate, and analyze the electrocardiogram. To set up the program, first we turned on the computer at our lab table while turning on the white interfacing box sitting on the table unless the green and red lights were already lit up indicating the box was turned on. Then, we opened the “Individual Cardiovascular Data” spreadsheet on the desktop and double clicked the icon “LoggerPro 2.2” to open the program. Next, we had to open a specific spreadsheet file, “EKG and Heart Rate” found under the folders “Sample Data” then “Biology”. Before beginning the program, the ECG electrodes were attached to the first subject. The adhesive electrodes were placed one on each upper arm and one on the right wrist, with the tab facing away from the subject’s body. The red wire was attached to the left upper arm, the green attached to the right upper arm, and the black to the wrist. Also, the pulse diode was attached to the subject’s pinky finger of the left hand so that the side with the light was over the fingernail. Once the equipment was attached correctly, the subject was to be completely still and relaxed, and we clicked the “collect” button so that the program started collecting the data. Once the sampling was over, the electrode cables were removed from the subject. After the electrocardiogram was analyzed, the process was repeated for the next subject.
To analyze the data collected by each electrocardiogram, we had to take some measurements. In order to determine pulse rate, in beats per minute, we moved the cursor over the peak of the first QRS complex and recorded the value displayed for time on the spreadsheet under the “First Peak” column. Then, the cursor was moved to the last QRS peak and the time was recorded under the “Last Peak” column. Then, we counted the number of pulse peaks and recorded this value on the spreadsheet under the “Number of Intervals” column. Once that information was recorded, the spreadsheet automatically calculated the average pulse rate. In order to determine pulse lag, we placed the cursor over the first QRS complex and recorded this value under the “QRS Peak” column on the spreadsheet. Then, the cursor was moved to the next peak after the QRS complex and this value was recorded under the “Pulse Peak” column of the spreadsheet. This process was continued for each QRS complex and its subsequent pulse peak. The spreadsheet automatically calculated the average pulse lag. In order to determine the P-T interval, we placed the cursor over the beginning of the first P wave and recorded the time under the “Start P” column on the spreadsheet. Then, we moved the cursor to the end of the T wave and recorded the time under “End T” column on the spreadsheet. We kept recording these data for the rest of the P and T waves. The average P-T interval was automatically calculated. Finally, in order to determine the T-P interval, we placed the cursor over the end of the first T wave and recorded the time under the “Start T” column on the spreadsheet. Then, we moved the cursor to the end of the first P wave and recorded the time under the “End P” column. We continued recording the times for the rest of the P and T waves. The spreadsheet automatically calculated the average T-P interval. All of these data averages were also recorded on the main computer at the front of the lab to be averaged with the rest of my lab section’s data.
Once all the resting measurements were recorded for each subject at the table, one at a time each subject completed thirty jumping jacks and quickly repeated taking their blood pressures and completing the process for collecting data from the electrocardiogram. These data were also recorded on the computer at the front of the lab to be averaged with the rest of the lab section’s data.
Results
Table 1. Comparison of Average Values, Chi-Square, and P-value for Pulse Rate, Pulse Lag, P-T Interval. T-P Interval, Systolic Blood Pressure, and Diastolic Blood Pressure.
Variable Average Before Exercise Average After Exercise Chi-Square P-value
Pulse Rate 75.4 beats/min 85.3 beats/min 1.64 0.2
Pulse Lag 0.366s sec 0.344 sec 2 0.157
PT Interval 0.643 sec 0.595 sec 8.909 0.003
TP Interval 0.235 sec 0.367 sec 2.33 0.127
Systolic Blood Pressure 114.5 mmHg 123.1 mmHg 2.91 0.088
Diastolic Blood Pressure 69 mmHg 79 mmHg 0 1
The treatments for this experiment were activities of measuring cardiovascular function before exercise and after exercise was completed, using the same group of subjects for each treatment. Because of this, we can conclude that this data should be analyzed with a paired chi-square median test. Table 1 shows that the probability that these results happened by chance for all of the variables except for the P-T interval was more than 0.05, which is low probability. So, we should reject only the null hypothesis which states that the P-T interval will be the same before and after the moderate exercise is completed.
Discussion
As shown in Table 1, on average, pulse rate increased after the moderate exercise, pulse lag decreased, the P-T interval shortened, the T-P interval lengthened, systolic blood pressure increased, and diastolic blood pressure increased. The paired chi-square median test for pulse rate gave a value of 1.64, so it makes sense that the p-value would be 0.2. This value is greater than 5%, or 0.05, so we do not have the evidence to reject the null hypothesis which states pulse rate will be the same before and after exercise. The literature reports that heart rate, or pulse rate, increases as muscles are being active in order to provide the muscles with needed oxygen supply (Starling’s Law of the Heart; Laughlin 1999). Average pulse rate increased during exercise as expected, however, the thirty jumping jacks were not a vigorous enough exercise to show significant change in pulse rate.
The paired chi-square median test for pulse lag gave a value of 2, and a p-value of 0.157. This p-value is greater than 5%, so we do not have the evidence to reject the null hypothesis which states that pulse lag will be different before and after exercise. According to Guyton (1985), heart rate increases due to the activation of the sympathetic nervous system. An increase in the depolarization of the SA node results from this stimulation. As heart rate increases, the depolarization of the SA node increases the contraction of the atria which increases the contraction of the ventricles at a faster rate. The exercise we completed was not energetic enough to increase the rate of this depolarization and yield a significant change in pulse lag before and after.
For the P-T interval the probability that the null hypothesis is true is very low as seen in Table 1. The p-value, 0.003, proves this. Because the p-value is below 5%, we have the evidence to reject the null hypothesis in favor of the research hypothesis. According to the literature, the P-T interval should shorten during exercise, which is proved in our results.
For the T-P interval, because the p-value is more than 5%, there is a high probability the null hypothesis is true, so we do not have the evidence to reject the null hypothesis which states the T-P interval will be the same before and after exercise. The T-P interval should shorten along with the P-T interval during exercise as the heart beats faster. Our results show an increase in the T-P interval. This is an error than could be resolved by completing a second trial to improve accuracy.
We initially predicted that blood pressure would increase due to exercise. The results in Table 1 show our prediction was correct. However, the p-values for both systolic and diastolic blood pressure are above 5%, so we do not have the evidence to reject the null hypothesis for both of these variables. This conclusion does not necessarily go against scientific theory discussed in the literature. According to Guyton (1985) and Marieb (1989), blood pressure increases due to sympathetic stimulation in working muscles. Our exercise did not require the muscles to work hard enough for vasodilation to occur in their blood vessels and vasoconstriction in the vessels of the rest of the body.
One major error during the experiment is that our results for a few of the variables show discrepancy in respect to scientific theory which required us to draw false conclusions. According to the literature, exercise should affect each variable. One explanation could be that the exercise performed did not make enough demand on the muscles, so the circulatory system did not react as predicted. For future investigations, we could perform a more intense exercise which would make more of a significant difference in the variables before and after the exercise was completed. In addition, according to Froelicher and Meyers (2000), it might be beneficial to use a different lead to carry out the ECG because placing the electrodes on the upper arms is not always reliable at detecting the cardiovascular effects of exercise. To illustrate, we could place an electrode on the chest of the subjects to achieve more accurate results.
in here…