Introduction
Research Question
Scientific Rationale
Hypothesis
- What is the effect of short term acute heat exposure on hematocrit, heart rate, weight, and blood pressure in college aged students?
Scientific Rationale
- Short term heat exposure can lead to increased sweat production. We know that if the body loses enough water through sweating that dehydration may occur. Dehydration may cause a rise in hematocrit levels because the volume of the blood decreases, and RBC per volume of fluid artificially rises.
- Dehydration also directly correlates to a reduction in cardiac output. Since tissues still need adequate oxygenation, the physiological effect of dehydration on the cardiovascular system would be tachycardia, or the increase in heart rate. Lack of fluid volume decreases blood pressure because the body does not have enough water to fill all the blood vessels, this results in a drop in systemic blood pressure.
Hypothesis
- We expect that acute heat exposure will cause a small increase in hematocrit, an increase in heart rate, a decrease in overall blood pressure and weight in college aged students based on the physiological facts stated above.
Methods
To complete this experiment, 6 students (3 male and 3 female) will begin by taking baseline values of heart rate, blood pressure, weight and hematocrit, using a pulse oximeter (Figure 5) to measure HR, a blood pressure cuff and stethoscope (Figure 2) to measure blood pressure, a scale to measure weight (Figure 6), and a micro capillary hematocrit reader (Figure 3), and capillary tube place blood inside. After baseline testing, students will go to the rec center and spend 20 minutes in a sauna (Figure1). The sauna was heated to 140 degrees Fahrenheit with 7% humidity (Figure 4). Once this is completed, students will take heart rate, blood pressure and weight again on site, and then take the hematocrit reading in the lab, percent change for all these variables will be calculated. The experiment was evaluated on December 4th, 2013 at 5 p.m. standard mountain time in Boulder Colorado, at The University of Colorado at Boulder.
RESULTS
Weight was less in the post heat exposure group, percent decrease of 1.56 percent, shown in Figure 1.
Hematocrit was less in the post heat exposure group, percent decrease of .5 percent, shown in Figure 2.
Heart Rate increased in the post heat exposure group, percent increase of 30.5 percent, shown in Figure 3.
Systolic blood pressure decreased in the post heat exposure group, percent decrease of 4.3 percent, shown in Figure 4.
Diastolic blood pressure decreased in the post exposure group, percent decrease of 2.8 percent, shown in Figure 5.
Comparison of all factors shows an average percent decrease in weight of 1.56 percent, an average decrease of hematocrit of .5 percent, an average increase of heart rate of 30.5 percent, an average decrease of systolic blood pressure of 4.3 percent and an average decrease in diastolic blood pressure of 2.8 percent. We used average percent change to accurately represent the changes from baseline to heat exposure of the dependent variables against each other. We understand that lab protocol does not allow us to graph more than one dependent variable on the same graph, but we do so for an easier comparison of variables.
Discussion
Our data supported our hypothesis that heart rate would increase while blood pressure and average weight would decrease. Our data did not support our hypothesis that determined hematocrit would increase. Our findings relate to previous research that confirms a relationship between heart rate and blood pressure in conjunction with heat exposure. In response to acute heat exposure the human body attempts to stay at homeostasis by facilitating loss of heat, there are two main mechanisms that exert this response. Sweating and peripheral vasodilatation in attempt to remove heat from the body core which releases heat by evaporative cooling and heat to the environment (Byrnes, Metabolism and Energy Balance). In response to the sympathetic control that causes vasodilatation, peripheral resistance decreases (Crandall, 1) Since blood pressure is a function of cardiac output and total peripheral resistance, and total peripheral resistance decreases in response to exposure to heat, cardiac output must increase to attempt to keep blood pressure at a relatively stable value. Cardiac output is a function of heart rate and stroke volume, therefore heart rate increases, whilst peripheral pressure decreases (Crandall, 1). This relationship between cardiac output and peripheral resistance therefore accounts for the results we obtained showing a decrease in blood pressure in account of significantly lower peripheral pressure, and a increase in heart rate in attempt to stabilize the equation. This constitutes extreme loss of body fluids, but our experiment did not allow for this condition to exist, therefore we could not properly test for sweat loss in relation to hematocrit levels. During our experiment one male subject found the heat exposure to be too overwhelming and cause excessive stress, which raised an ethical issue. A methodological flaw that we encountered was when subjects walked from the sauna back to the lab to measure hematocrit, they were exposed to extreme cold. This can cause peripheral vasoconstriction which could potentially cause the micro capillary tube to not be representative of arterial blood. The practical implications of our findings conclude that heart rate and blood pressure as well as weight are affected by acute heat exposure, therefore we can broadly conclude that people with heart disease or people with sympathetic nervous system problems should not go in saunas. Also medically confirmed data also concludes that infertility in males may arise from frequent exposure to saunas (Jurewicz, 6). Further research could include analyzing how chronic heat exposure changes the response of heart rate, blood pressure, hematocrit and body weight.
"References"
Response to Increased Temperature. Byrnes, William. "Metabolism and Energy Balance." Physiology 3480. GOLD A2B70, Boulder. Sept 12. 2013. Lecture.
Heat Stress and Baroreflex Regulation of Blood Pressure
CRAIG G. CRANDALL
Med Sci Sports Exerc. Author manuscript; available in PMC 2010 February 10.Published in final edited form as: Med Sci Sports Exerc. 2008 December; 40(12): 2063. doi: 10.1249/MSS.0b013e318180bc98
Gersten, Todd. "Hematocrit." MedlinePlus Medical Encyclopedia. A.D.A.M., Inc., 8
Feb. 2012. Web. 8 Dec. 2013. <http://www.nlm.nih.gov/medlineplus/ency/
article/003646.htm>.
"Hematocrit: MedlinePlus Medical Encyclopedia." U.S National Library of Medicine. U.S. National Library of Medicine, n.d. Web. 06 Dec. 2013.
Pictures:
"A Low Heart Rate – What Can It Possibly Mean For You?" Azumio. Azumio, Inc.,
n.d. Web. 8 Dec. 2013. <http://www.azumio.com/low-heart-rate/>. Heart
rate large
Afanasyeva, Kristina. "Illustration - Heart Rate Vector Design Element."
123rf. 123RF Limited, n.d. Web. 8 Dec. 2013.
<http://www.123rf.com/
photo_4819916_heart-rate-vector-design-element.html>. Small Heart Rate
Effective Learning. ELS Audio Publishing, LLC, n.d. Web. 8 Dec. 2013.
<http://www.effectivelearning.com/>. Scale
Fankhauser, David B., Ph.D. "HEMATOCRIT PROTOCOL." Biology at Clermont College.
N.p., 2009. Web. 8 Dec. 2013. <http://biology.clc.uc.edu/fankhauser/Labs/
Anatomy_%26_Physiology/A%26P202/Blood/hematocrit_use/Hematocrit.htm>.
Hematocrit
"Infrared Saunas by Sunlighten wirelessly measure heart rate and calories
burned!" Trendir. Lillian Pikus, 1 Mar. 2010. Web. 8 Dec. 2013.
<http://www.trendir.com/archives/004194.html>. Sauna
Scott. "What are the best ways to lower blood pressure naturally?" Today I Found
Out. Vacca Foeda Media, 28 Feb. 2013. Web. 8 Dec. 2013.
<http://www.todayifoundout.com/index.php/2013/02/
what-are-the-best-ways-to-lower-blood-pressure-naturally/>. Blood Pressure
Heat Stress and Baroreflex Regulation of Blood Pressure
CRAIG G. CRANDALL
Med Sci Sports Exerc. Author manuscript; available in PMC 2010 February 10.Published in final edited form as: Med Sci Sports Exerc. 2008 December; 40(12): 2063. doi: 10.1249/MSS.0b013e318180bc98
Gersten, Todd. "Hematocrit." MedlinePlus Medical Encyclopedia. A.D.A.M., Inc., 8
Feb. 2012. Web. 8 Dec. 2013. <http://www.nlm.nih.gov/medlineplus/ency/
article/003646.htm>.
"Hematocrit: MedlinePlus Medical Encyclopedia." U.S National Library of Medicine. U.S. National Library of Medicine, n.d. Web. 06 Dec. 2013.
Pictures:
"A Low Heart Rate – What Can It Possibly Mean For You?" Azumio. Azumio, Inc.,
n.d. Web. 8 Dec. 2013. <http://www.azumio.com/low-heart-rate/>. Heart
rate large
Afanasyeva, Kristina. "Illustration - Heart Rate Vector Design Element."
123rf. 123RF Limited, n.d. Web. 8 Dec. 2013.
<http://www.123rf.com/
photo_4819916_heart-rate-vector-design-element.html>. Small Heart Rate
Effective Learning. ELS Audio Publishing, LLC, n.d. Web. 8 Dec. 2013.
<http://www.effectivelearning.com/>. Scale
Fankhauser, David B., Ph.D. "HEMATOCRIT PROTOCOL." Biology at Clermont College.
N.p., 2009. Web. 8 Dec. 2013. <http://biology.clc.uc.edu/fankhauser/Labs/
Anatomy_%26_Physiology/A%26P202/Blood/hematocrit_use/Hematocrit.htm>.
Hematocrit
"Infrared Saunas by Sunlighten wirelessly measure heart rate and calories
burned!" Trendir. Lillian Pikus, 1 Mar. 2010. Web. 8 Dec. 2013.
<http://www.trendir.com/archives/004194.html>. Sauna
Scott. "What are the best ways to lower blood pressure naturally?" Today I Found
Out. Vacca Foeda Media, 28 Feb. 2013. Web. 8 Dec. 2013.
<http://www.todayifoundout.com/index.php/2013/02/
what-are-the-best-ways-to-lower-blood-pressure-naturally/>. Blood Pressure