Effects of Temperature on Blood Pressure
Sarah Gardner, David Hoch, Bryan LaFonte
CU Boulder, Fall 2007
We tested the effects of temperature changes on human blood pressure. As one of the vital signs, blood pressure is a helpful indicator of the body’s internal conditions. It is the measure of force against the arteries as blood is pumped throughout the body (Van Voorhees 2006). Blood pressure is constantly changing to maintain homeostasis within the body. Since temperature change can disrupt homeostasis, we predicted that blood pressure will adjust to maintain body heat. This will lead to a rise in blood pressure when temperatures drop and a drop in blood pressure when temperatures rise. We also predicted that heart rate will remain constant to avoid another deviation in homeostasis. Our hypothesis is that blood pressure will rise in cold temperatures, and lower in hot temperatures.
To test this hypothesis, we measured the subject’s blood pressure while they were seated with their right hand in a beaker of cold water (5°C), hot water (42°C), and room temperature water (23°C). Heart rate was measured to have a comparison against changes in blood pressure. This was done by taking the radial pulse of the left hand. We took three measurements of blood pressure and heart rate for each of the three beakers of water; the first after initial exposure, the next after 1 ½ minutes, and the final after 3 minutes of exposure. We predicted that the average blood pressure in the cold water would be higher than the average blood pressure in the hot water.
Our T-Test for means indicated that the blood pressure after exposure to cold temperatures was significantly greater (p=3.6 E -4) than the blood pressure after exposure to hot temperatures; with the average for the cold water being 133/90 mmHg and the average for the hot water being 121/78 mmHg. The average blood pressure for the room temperature water was 113/68 mmHg. There was no significant difference (p=0.29) between heart rates for the hot, cold, or room temperature water trials, for which the averages were 74, 76, and 76 bpm, respectively. Our regression tests showed that blood pressures for the cold water had a tendency to rise over time (R2=0.71), while the tendency of blood pressures in the hot water was to lower (R2=0.99).
The results were consistent with our predictions; blood pressures were higher after exposure to cold water than exposure to hot water, while maintaining heart rate. This mechanism, increasing blood pressure without having to increase heart rate, prevents loss of body heat and helps sustain homeostasis. The major problem we encountered was the significant amount of time needed for each trial, preventing us from acquiring a large sample population and reducing the validity of our experiment. Human error while measuring blood pressure and heart rate could have also been a potential problem. Although our predications were confirmed by the results, our hypothesis was not completely accurate. Blood pressures after exposure to the hot water did lower, but after they rose initially. This resulted in a higher average blood pressure for the hot water results than the room temperature water results. An alternative hypothesis that would be more consistent with our results would state: blood pressure will increase after exposure to cold temperatures and decrease after a time of exposure to hot temperatures.
Van Voorhees, Benjamin W. “Blood Pressure.” Medline Plus. 21 Jul 2006. U.S. National Institute of Medicine and the National Institutes of Health. 10 Nov 2007. <http://www.nlm.nih.gov/medlineplus/ency/article/003398.htm>.