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Neeraj Chawla

Lab Report
Gas Exchange - Factors affecting Lung Capacity

Hi

My class just completed the entire SL/HL syllabus part of human physiology, and now we have to complete a lab report on a factor that affects total lung capacity (which averages at about 6 decimeters cubed per person, but obviously can be significantly lower) - and I dont exactly know what single factor I think would be really appropriate to 'change' (independent variable). Could someone give some ideas (looking at height, weight, standing/sitting, smokers vs non smokers etc) and could you possible give a reason as to how these/this particular factor(s) affect lung capacity?

Anybody's assistance will be greatly appreciated, and I would really like to get replies ASAP, preferably within the next several hours so I can start writing up my design.

Thanks

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Well height, weight (only to an extent), gender and ethnicity all have an impact on TLC. How are you intending to measure TLC? You should take care that you're using the right terminology. The best way to explain it is really with this sort of a graph: CLICK

You can see that total lung capacity is equal to forced vital capacity plus 'dead space' or residual volume, they both refer to the same thing. Basically we always have some air left in our lungs otherwise they'd collapse down completely and it would take massive effort to get air in again. The only real time we have collapsed lungs is when we're born and take our first breath which should inflate the lungs up from nothing - after that, all things being well, we have dead space. The only real way to measure dead space is stuff like using noble gases in inspired and expired air and looking at volume changes and so on, which I somehow doubt you're doing.


So, make sure your terminology is right. If you're looking at forced vital capacity, make sure you say that and NOT total lung capacity. Equally make sure you're not using a peak flow meter and measuring FEV1.

To be honest I don't know if this is a very good lab project because there aren't really any independent variables that you can easily change, they're all pretty intrinsic to a person - you can't really change the variable of 'height' within somebody! So sure you can test people of several different heights but it's difficult to control for all the multiple other factors. It would be much better to do something where you could alter the factor within the same person. For FVC I don't think it's really possible. But if your teacher has told you to do something on this, I would probably look at height (but do your best to control for gender and ethnicity - make sure all your volunteers are uniformly male/female and of the same ethnicity).

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wow.. that cleared up a lot for me.. my teacher wasn't very clear about everything but I have a better idea of the appropriate terminology and methods. Additionally, for this sort of experiment, would you personally do a statistical t test if given the option? my teacher has given the option, but says it isnt required to any extent, but could be useful if looking at height vs fvc (as i think i will probably look into this)

thanks

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Be careful with the smokers and non-smokers since they would have to be of the same age and having had smoked for the same period of time, as well as ideally of the same sex (although the latter would not be necessary).

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