|MadSci Network: General Biology|
Jeff, This is a nice easy question for a change. I like it very much.
Temperature is always a controlling factor for chemical reactions. Having said that, it follows that the heart beat is a function of chemical processes. The heart beats in response to an electrical impulse in all the myocardial (heart muscle) fibers that initiates a chain reaction starting with calcium interacting with some complex protein molecules in each of the cells. This Ca— protein interaction brings about the contractile event and is a chemical reaction using ATP (adenosine triphosphate) as the energy source to drive each contraction.
Way back in the 1960s, I learned in my physical chemistry class that a chemical reaction approximately doubles its rate every time you increase the temperature 10 degrees centigrade, and approximately halves its rate every time you decrease the temperature 10 degrees centigrade. Therefore, when you catch a cold and begin to run a fever (elevated temperature) all chemical processes in your body will speed up a little bit. This will happen without any increased physical activity. If you fall overboard in the winter into cold water, you depress your temperature and all the chemical process will slow down a little bit, unless you don’t get hauled out of the water quickly, in which case your chemical process would come to a complete halt. Not a happy thought but something one needs to consider when going out on the water when it is very cold.
So you see that an increase in temperature upward from 37 C (normal value) would definitely increase the heart rate in a direct correlative manner. This is due, at the most basic level, to the increase in atomic and molecular movement (Brownian motion) that occurs with heating any system including the body. Just like heating water makes the molecules move around faster and eventually boil off into the air if heated greatly, the molecules in our bodies bump each other much more frequently when the temperature goes up and this increases the chemical rates of reaction. If you have any further questions about this feel free to ask me.
Try the links in the MadSci Library for more information on General Biology.