Travis Kelly

Jonathan Nelson


Homeostatic responses of the Circulatory System: The effects of Ambient Temperature on Heart Rate and Blood Pressure


Homeostasis is the body’s attempt to maintain equilibrium within a wide range of environments. The circulatory system of mammals maintains homeostasis by the heart and blood vessels working together to maintain a healthy flow of blood throughout the rest of the body. The purpose of this study was to see what kind of homeostatic circulatory response would be exhibited when the temperature immediately around the human body changes and the effects of that response. Our hypothesis is that temperature affects blood pressure and heart rate.


We hypothesize this because of vasoconstriction and vasodilation. The heart and blood vessels can change very rapidly to maintain a healthy blood flow to the rest of the body. The heart can adjust its speed to pump more or less blood throughout the body. Blood vessels can change their size to act as thermo-regulators for the body. Muscle around the walls of the blood vessels contract to shrink the diameter of the blood vessel, this is called vasoconstriction. Vasoconstriction acts as a way to slow down the flow of blood and restrict heat loss. Also vasoconstriction increases vascular resistance, thus increasing blood pressure. The opposite of vasoconstriction is vasodilation. Vasodilation is when the blood vessels dilate to increase blood flow and reduce vascular resistance, thus reducing blood pressure. It also is important in radiating excess heat from the body.   


To simulate different environments we took our heart rate and blood pressure at room temperature, in a sauna, and an ice bath. Measurements were taken 3 times with 5 minutes in-between each measurement.


The data shows a relation between ambient temperature and blood circulation but does not give us a trend to see what the effects will be in certain temperatures. The average heart rate at room temperature was 76.32 bpm, in the sauna 104.8 bpm, and in the ice bath 81.5 bpm. A t-test for the different temperatures revealed P-values for 25° to 60°=.000376389, 25° to 9°=.614771291, and 60° to 9°=.109866501. Significant change was only noticed between the normal and hot temperature. There is an obvious physiological response to the different temperatures. In the hot environment there should have been a more obvious decrease in blood pressure due to vasodilation thus reducing vascular resistance. In the cold environment there was an obvious increase in blood pressure due to vasoconstriction thus increasing vascular resistance.


Our results are consistent with our hypothesis however since our hypothesis was broad we achieved broad results. There were noticeable changes but we do not have enough data to make any further conclusions about the experiment. Variables like duration of time, number of test subjects, equipment, temperature variance could be changed to give more precise results that show the different kinds of relationships between ambient temperature and blood circulation.