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Thread: How to calulate tidal volume and ventilation rates?

  1. #1 How to calulate tidal volume and ventilation rates? 
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    Hi, how do I calculate the tidal volume and ventilation rates for two test subjects from the number of observed breaths per minute taken during an experiment?

    I also need to calculate the stroke volume of the heart and the cardiac output, but I have no clue how to do this?

    The relevant details are as follows:

    Subject 1

    Breaths per minute at rest:

    24

    Breath per Minute during exercise:

    29

    Heart Rate during rest:

    97

    Heart Rate during exercise

    165

    Age 27

    Weight 84KG

    Subject 2

    Breaths per minute at rest:

    16

    Breath per Minute during exercise:

    22

    Heart Rate during rest:

    74

    Heart Rate during exercise

    23

    Age 17


    Weight 72KG

    Any help anyone can offer would be greatly appreciated.


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  3. #2  
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    Edited with weight info in case it's needed. BTW can this even be done? I can't find any info on the web anywhere about it.


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  4. #3  
    Forum Professor Zwirko's Avatar
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    You can't calculate stroke volume or cardiac output from the data that you provide. The best you could do would be to look up typical values for an "average man".

    For tidal volume, again you'd need to take a typical value: Wikipedia suggests 7ml/kg. So for subject 1 you'd get 0.588 litres. From there it should be easy to get a measure of the ventilation rate (tidal volume X respiratory rate, for example).
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  5. #4  
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    Lol, my maths might be a little shaky. But is that 7ml *per* KG? (It looks a bit like 7ml divided by the net KG weight the way it's written).

    If it's 7ml per KG, as far as I can work out for subject 1 in our test, with a weight of 84KG the tidal volume should be given as 84 x 7 this gives an answer of 588ml (which is equivalent to 588 cm^3 ) at rest.

    To derive the ventilation rate the standard calculation is breathing rate x tidal volume = ventilation rate. So in this case this would give a figure of 24 x 588 = 14112. (Which is 24 breaths per minute at rest.)

    This seems high, but it's only because this person is really unfit. However clearly these numbers are different from yours. But if I do it as 24 x 0.588 I get an answer of 14.112 cm^3 per minute, which seems like a tiny amount.

    I also don't know how to do this calculation for someone during exercise, since clearly the tidal volume will increase as the level of exercise increases?

    PS

    I'm a mature student and it's a really long time since I have done anything like this, including maths. So please forgive my questions if they seem dumb.
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  6. #5  
    Forum Professor Zwirko's Avatar
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    Yeah, 7 ml for every kg of body mass.

    7 ml * 84 kg = 588 ml per kg. Best to put in litres, so it'd be 0.588 L. But that's just for an average Joe - maybe subject 1 only has one lung or has smoked too much? Can't tell.

    For ventilation rate it'd be 24 * 588 = 14.1 litres per minute.

    Again, there doesn't seem to be enough information there to allow one to calculate the increased tidal volume during exercise for each subject. But I'm no expert on human physiology, so maybe I'm just confusing things here...
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