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10 Mar 2004

Matric assistance
Hello, I wonder if you can give me a bit of help. I am a matric student and have to devise an experiment for Biology and i am at a bit of a loss as to how to go about it. I have to do an experiment on the effect of excercise rate on the breathing rate. It has to consider CO2 levels in the blood, cardiac rate, and we have to make use of a respiromator in the experiment.

Would you be able to guide me at all as to what I could follow for this portfolio.
Answer 360 views

01 Jan 0001

HI Annie

Sure, although if you want to do a really good project, there are a few books I can recommend on the subject, but I'll get to that later.

A respirometer is a device that measures respitory rate - by respiratory rate, I mean how fast you breathe. It also measures how much you breathe - volume. Remember that total ventilation is a product of the rate of breathing, and the depth of breathing. So, for example, if you are breathing at 12 breaths per minute, and each breath is 500 ml (both normal resting values), then your volume breathed per minute (called the minute ventilation) is 6 L/min.

Now, in your experiment, what you have to show is that as you exercise harder, your minute ventilation goes up. THis happens because BOTH the rate of breathing and the depth of breathing go up. So, at rest you might be breathing 12 times a minute, and each breath is 500 ml, as I just explained. But, when you are exercising as hard as possible, then it's possible to breathe at a rate of 60 to 80 breaths per minute, and the volume each time you breathe can be as high as 3 L. THis means that the total minute ventilation can be as high as about 180 L/min. Compare this to the normal resting value of 6L/min, and you can see that the ventilation can increase by 30 fold!

So, what happens during exercise is that you first get an increase in the breathing rate, and then you get an increase in the depth of breathing a little later on - this results in a very big increase in total ventilation

To design an experiment, you would have to be creative - you have a device that allows you to measure ventilation, and so now you would have to do something to change exercise intensity. For example, you could use a treadmill and set it at different speeds (say, 5 km/h, 6 km/h, 7 km/h and so on, up to about 12 km/h). Someone could run on the treadmill for one minute at each speed, while you measure their breathing. This would show you that as they get faster, their breathing rate goes up.

As for heart rate, it goes pretty much the same way. As you exercise harder and harder, the heart rate goes up. You can measure this using a heart rate monitor.

The CO2 levels in the blood are a little more complicated. The basics are that as you exercise progressively harder, your CO2 leves go up. This happens because the muscles burn fuel when you exercise, and the by product of this metabolism is CO2. So, your breathing rate goes up, which allows more oxygen to get to the muscles, and also the CO2 levels in the blood go up. I won't get too indepth here, but the increase in CO2 is actually quite important, because it helps with the increase in breathing and also with more oxygen delivery. The end result though is that you breathe off CO2 - in otherwords, when you breathe out, you get rid of the CO2, which allows your body to regulate itself quite well.

I hope all this helps start you off at least. I'm sure that if you give it some thought, you'll see other ways to do this. As for a book, Lore of Running by Tim Noakes is excellent and well worth looking at - of course, you don't want to buy something like this just for once off use, but I'm sure that a local library might be able to assist.

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