Lab Principles Report
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Table 1: Hypotheses
Inquiry Null Hypothesis Alternative Hypothesis
1 There is no statistically significant difference in
duration of the QRS complex in the supine condition of the
experiment between males and females ages 19-28.
There is a statistically significant difference in
duration of the QRS complex in the supine condition of the
experiment between males and females ages 19-28.
2 There is no statistically significant difference in heart
rate during the supine condition recording between those who regularly exercise and those
who do not.
There is a statistically significant difference in heart
rate during the supine condition recording between those who regularly exercise and those
who do not.
Materials and Methods
Materials, Set-Up, Sampling Groups
The materials for this experiment include: BIOPAC Student Lab System (BSL 4, MP36, MP35, or MP45 ) on a PC ( Windows 8, 7, Vista XP, Mac OS X 10.5 – 10.8), BIOPAC Electrode Lead Set (SS2L), BIOPAC Disposable Electrodes (EL503,) each subject only uses 3 electrodes, BIOPAC Electrode Gel (GEL1) and Abrasive Pad (ELPAD) or Skin cleanser or alcohol prep, and a comfortable mat/cot/pillow for subject when they are in the supine position.
Five minutes before turning the system on and beginning calibration, each subject was prepped before placing the disposable electrodes on the skin. This includes clearing electrode sites of jewelry or clothing, cleaning the skin where the electrode will be placed with alcohol or soap and water, and adding a drop of GEL1 to the electrodes if they are dry prior to adhesion to subject. Place the white lead (negative electrode) on the right anterior forearm on the wrist, the black lead (ground electrode) on the right medial surface of the ankle, and the red (positive electrode) on the left medial surface of the ankle. Have the subject lay in a relaxed supine position with their eyes closed and start the BIOPAC Student Lab program to begin the 8 second calibration.
In this experiment four conditions will be evaluated and recorded. These are supine position, seated upright position, breathing deeply while sitting in an upright position, and after 30 half jacks of exercise. Each condition has an ECG recorded for 20 seconds as well as the heart rate.
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Overall, there were thirty (30) test subjects being studied; thirteen (13) males, twelve (12) females, and five (5) unreported sex subjects. Each data set from Fall 2019 and Summer 2019 classes contained two different subjects each examined them under all four conditions mentioned above. Each subject gave their age and answered yes or no to the question, “Do you perform regular exercise?” Fifteen (15) subjects said they did regularly exercise, ten (10) subjects said they did not regularly exercise, and five (5) subjects did not report an answer. In all data analysis the unknown gender and unknown answer data were omitted to prevent the unintentional addition of bias to the data sets.
ECG Experimental Procedure
In every condition listed above the same general procedure was followed for each subject. Before any measurement was taking a calibration did take place 5 minutes after having the electrodes on the skin. To ensure optimal data a subject must relax their arms and legs, eyes closed, remain still and not talking, and check that the electrodes do not peel up. After recording the ECG for 20 seconds on the BIOPAC software ensure that the data is similar to the example data, if not a redo is permitted. This means no excessive baseline drift or electromagnetic artifact or noisy/flatline results. It is important to note that the recording is not stopped but suspended, this means all four conditions are in the same “experiment file.” For all experiments if the data produced is shifted or not similar to the example a redo must be performed by that section in the BIOPAC system.
Although each condition has a similar procedure there are a few variances. In the supine position the subject only needs to be laying down and the recording can proceed. Before the seated condition the subjects need to stand up and then settle into the position. The position is sitting upright with both hands relaxed and apart on their respective thighs with palms facing towards the ceiling. You may record this condition as soon as the subject is seated, breathing normally and relaxed. For deep breathing the subject remains in the previous position but inhales and exhales slowly for five prolonged breath cycles. At each inhale the recorder presses F4 and then F5 at the start of the exhale. There is a difference in time recording for deep breathing and after exercise. The duration for the deep breathing test is as long as it takes for the subject to have the five prolonged breath cycles. The duration for the after-exercise test is 60 seconds after performing a rapid elevating heart rate exercise; in this experiment 30 half jacks were performed.
Data Analysis
Using the BIOPAC software several data measurements were taken. This included HR during different cardiac cycles, ventricular systole and diastole duration and measuring how long (ms) and at what amplitude (mV) certain portions of the signal occurred. With three HR trials and three Supine test trials the following data analysis will consider solely the mean values presented. In the data analysis however, a t test (alpha =0.05) was performed per hypothesis group and a bar graph of the means with plus/minus one standard deviation error bars. The t-test performed was a two-sample t Test assuming unequal variances in Microsoft Excel.
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Results
Inquiry One:
The first analysis of the data set from the experiments is over the duration (ms) of the QRS Complex between males and females when performing the supine condition. Overall, there were 39 data points for the males and 36 data points for the females (see Appendix, Table i). There were some data sets that did not include their sex/answer, to prevent unintentional bias being added to data analysis, these results were omitted. In order to obtain the duration, the user used the BIOPAC Software to review the saved data from the experiment and was able to determine the time intervals. These values were entered into an excel spreadsheet.
The average duration of the QRS Complex for males was 92.66 ms +/- 23.27 ms. For females the average duration was 87.0277 ms +/- 23.82 ms. With a two-sample t-Test assuming Unequal Variances (542 vs 567), the p value associated with these two groups is 0.304. The alpha value for this test was 0.05. It is important to note that a Z-test was not used even though the sample size was greater than 30 people. This is because a population standard deviation is not known at this time and a normal distribution could not be assumed. The means were analyzed further for these groups because no apparent trends or general values were apparent in a scatter plot (Fig. 1).
Figure 1: A quick overview of the observation values shows no distinct trend towards a certain duration period. Overall, the general range presented is within normal limits according to the BIOPAC Procedure (60 ms to 120 ms).
In order to get a representative value for the entire experiment each group performed three trials for each of the four condition types and a mean for each ECG Component was compiled. However, to prevent
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misleading values all three trial values were complied in order to calculate the sample mean and other analytic values. The means between the two independent groups with error bars are shown in Fig. 2, their associated p-value was 0.3040 (see Appendix, Table 2).
Figure 2: Means of how long in ms the duration of the QRS Complex was for males and females while lying in the supine position
Inquiry Two:
The second analysis of the data set from the experiments is over the heartrate (beats per minute, bpm) during the supine condition between those who exercised regularly and of those who did not. Overall, there were 45 data points for the yes answer and 30 data points for the no (see Appendix, Table 3). There were some data sets that did not include their sex/answer, to prevent unintentional bias being added to data analysis, these results were omitted. In some capacity those who work out are said to have a lower heart rate range. In general, after exercise these individuals return to a resting heart rate faster than those who do not exercise regularly. With this commonly understood trend an additional data set was analyzed. The subjects who answered “yes” to regularly exercising but had a heart rate higher than 100 bpm after exercising had their data points shifted to the “no” category. The two analyses will be differentiated clearly. In order to obtain the heart rate, the user used the BIOPAC Software to review the saved data from the experiment and was able to determine the rate by measuring the R-R interval between two signal formations. These values were entered into an excel spreadsheet and indicated clearly from which trial they occurred and from which condition.
A t-test was performed between both yes groups and both no groups to see if the mean difference was statistically significant. The p value for the “Yes” answer was 0.0705 with an alpha of 0.05 (see Appendix, Table 4). The p value for the “No” answer was 0.56 with an alpha of 0.05 (see Appendix, Table 5).
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The average heart rate for those who exercise was 72.18 bpm +/- 8.343 bpm. For those who do not exercise the average heart rate was 71.3626 bpm +/- 16.67 bpm. After shifting the data to potentially fit with trends the following averages were obtained. The second average for those who exercise was 68.43 bpm +/- 7.88 bpm. For those who do not exercise the second average heart rate was 72.5685 bpm +/- 14.41 bpm.
With a two-sample t-Test assuming Unequal Variances (69.61 vs 277.5), the p value associated with these two groups is 0.805. The alpha value for this test was 0.05 (see Appendix, Table 6). For the second data compilation, a two-sample t-Test assuming Unequal Variances (62.02 vs 207.58), the p value associated with these two groups is 0.047 with the same alpha value =0.05 (see Appendix, Table 7). Although the scatter plot showed a tighter range with the adjusted values (Fig. 3) than the non-adjusted (Fig. 4) it is important to further analyze the data.
Figure 3: A quick overview of the observation values shows no distinct trend towards a certain heartrate. Overall, the general range presented is between 45-85 bpm while resting.
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Figure 4: A quick overview of the observation values shows no distinct trend towards a certain heartrate. Overall, the general range presented is between 45-85 bpm while resting. However, the plot tends to be denser and closer together than the non-
adjusted values.
Similar to the first inquiry two bar graphs were made to show the means for each group. The data had been compiled from the three heart rate trials that occurred during the supine condition. However, to prevent misleading values all three trial values were compiled as opposed to their individual means in order to calculate the sample mean and other analytic values. The means between the two independent groups with error bars are shown in Fig. 5 and Fig 6.
Figure 4: Means of heartrate in beats per minute while lying in the supine position between those who exercise regularly (non- adjusted) and those who do not (non-adjusted).
Figure 5: Means of heartrate in beats per minute while lying in the supine position between those who exercise regularly (adjusted) and those who do not (adjusted).
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Discussion and Conclusion
Inquiry One:
The first data analysis of this experiment was aimed at determining if there was a statistical difference in duration of the QRS Complex wave during a 20 second ECG Recording while the subject is laying down in the supine position. This examination focused on the variable of gender. An interesting fact is that the mean weight of the heart in a man is 280-340g and in a woman the weight is 230-280g. Although these values change depending on the sample of cadavers and their overall health, normally men have heavier hearts [4]. I wanted to see if the different sizes of the heart would translate into significant differences between the cardiac activity. Although the same process would occur, if the woman’s heart is generally smaller does it beat faster in order to compensate for the lack of volume when looking at their male counterpart? The QRS Complex is essentially the representative action of depolarization of the ventricles. Would the smaller female heart take a smaller duration to complete the task when compared to the male? Is this why the standard deviation was smaller for females than males? With this set of data, we fail to reject the null hypothesis. Gender made no statistical difference in the duration of the QRS Complex Wave. The p value was 0.304 with an alpha of 0.05.
If someone wanted to explore the effects that gender has in cardiac composition that would be an interesting study. It would be beneficial to see how these differences translate into the physiology of the heart. Hopefully a smaller alpha level could be used to reduce the chance of a Type I error from happening. If there are in fact differences between the genders then more specialized medications and treatments can be performed. Are these differences more impactful as we age?
Although I did not personally take the data for these experiments, it is safe to say that the data provided has an assumed level of accuracy. All groups were given sample data to compare to and the option of redoing a section with little difficulty in order to obtain a better result. Errors in this experiment can be made from data points not having enough accuracy. Participants also had no obvious reasons to lie about their gender, but this still may have occurred.
Inquiry Two:
The second data analysis of this experiment is focused on the heart rate between those who exercise and those who do not. Two categories of this experiment analysis were made. Adjusted answers versus Non-Adjusted Answers. I personally adjusted the answers from subjects with the answers “yes” heart rate data to the “no” category if their heart was above 100bpm immediately following exercise. This was the final condition that was mentioned in the procedure.
With this being a personal question, some people may lie and say they exercise regularly when they do not. Although the heart rate does rise during exercise the rate at which it returns to normal is quicker in those who exercise. One study focused on the heart rate recovery between marathon runners and untrained controls also supports the previous statement [5]. This is in relation to the parasympathetic nervous system. Athletes normally have lower resting heart rates also because of reactions in the sympathetic system. It is unlikely that the young adults
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represented in the data set have such differences in exercise performances as the aforementioned study. For this reason, the following conclusions with my hypothesis are strictly related to the participants in the study. They should not be used to represented entire populations.
For the non-adjusted or original data answers, we fail to reject the null hypothesis. Exercising regularly did not make a statistical difference in resting heart rate during the supine condition of the experiment. The p value was 0.805 with an alpha of 0.05. For the adjusted or shifted data answers, we reject the null hypothesis, the p value was 0.047 with an alpha of 0.05. Exercising regularly did make a statistical difference in resting heart rate during the supine condition of the experiment.
A future continuation of this study may find it beneficial to study the effects of exercise on heartrate during the timeframe of a year. Some participants could increase exercise frequency/intensity, some may decrease, and some may continue what they are already doing. These different variables may be able to show how effective exercise can be to our cardiac health and potentially identify when the benefits are not substantial What is the perfect “dose “of exercise for improving cardiac health?
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References
1. Ashley EA, Niebauer J. “Cardiology Explained”. London: Remedica; 2004. Chapter 3, Conquering the ECG. Available from: https://www.ncbi.nlm.nih.gov/books/NBK2214/
2. Becker, Daniel E. “Fundamentals of electrocardiography interpretation.” Anesthesia progress vol. 53,2 (2006): 53-63; quiz 64. doi:10.2344/0003- 3006(2006)53[53:FOEI]2.0.CO;2
3. Yang, Xiang-Lin et al. “The history, hotspots, and trends of electrocardiogram.” Journal of geriatric cardiology : JGC vol. 12,4 (2015): 448-56. doi:10.11909/j.issn.1671-5411.2015.04.018
4. Mohammadi, Shabnam et al. “Study of the normal heart size in Northwest part of Iranian population: a cadaveric study.” Journal of cardiovascular and thoracic research vol. 8,3 (2016): 119-125. doi:10.15171/jcvtr.2016.25
5. Du, Na et al. “Heart rate recovery after exercise and neural regulation of heart rate variability in 30-40 year old female marathon runners.” Journal of sports science & medicine vol. 4,1 9-17. 1 Mar. 2005