Any physicists out there?

[yorkie_chris]

Forgot to mention ... you silly medic, physicists are no good in the real world, you want an engineer

[the_lone_wolf]

Originally Posted by Dr Rich

But focussing on the deadspace issue, we normally say that its the increase in deadspace volume that causes problems breathing through tube. Dont try it but believe me it will. But although you cant breathe properly through a 3m tube that is say 1cm wide as deadspace is then an extra 300ml (your own is about 200ml), obviously you could have a tube 30cm long and 10cm wide, which would be fine but the volume is the same.

the volume of those two tubes is not the same though, note that the volume of a cylinder (or your circular tube) is proportional to it's length, but proportional to the square of it's diameter

volume of your tube equals length multiplied by pi multiplied by the radius squared

therefore tube one is 3m long and has an internal diameter (for argument's sake) of 0.005m (half of 1cm, remember radius not diameter) - the volume is 3.142 * 3 * (0.005)^2 = 0.000236cu.m

tube two has length 0.3m and internal diameter 0.1m, therefore the volume is 0.00236cu.m

so tube two actually has ten times the volume of tube one...

i'm not understanding what you mean with dead space however, if you want to explain it to a physicist with no medical knowlegde i'll have a stab though

Surely the ultimate question is whether you could still make that annoying slurpy-suckey noise whilst attempting to drain the last dregs of cola from the bottom of a glass by using a 3m long straw?

[yorkie_chris]

Yes but it would depend on the surface tension of cola, and the distance between the edge of the tube and the bottom of the glass. I also have a suspicion that the shape of the tube walls would play a part as well as the usual wall conditions determining pressure loss, and hence possible flow...

Oh wait, you were taking the pi$$....

[the_lone_wolf]

Originally Posted by yorkie_chris

Yes but it would depend on the surface tension of cola

the relevant contact angle wouldn't just depend on the surface tension of the cola, you also need to consider the relative hydrophobicity/hydrophilicity of the material used to construct the container or straw and their microscopic structure...

Ah yes, the volume calcs are wrong, doh. However I think the problem remains the same as if volume were the determinant as you commonly read then tube 2 would be much much worse in this scenario, which it isnt for the reasons well put.

As someone said above not all the fresh air we breath in gets to the area where gas is exchanged or is used in exchange. Deadspace is the volume of the respiratory system that is not involved in gas exchange. Anatomical deadspace is the trachea and bronchi, where you will not absorb O2 and shed CO2. That deaspace contains a stale air mix which gets taken back into the lungs in the next breath, also. Alveolar deadspace is unperfused or unventilated alveoli (where gas is exchanged), and can be considered negligible for the purposes of this in a normal individual. Deadspace is about 150 to 200ml. So of a typical 500ml breath in we only use about 350ml or so in gas exchange. So the tube adds deadspace to that value, in the case of a tube maybe another 350ml, the total deadspace is 500ml. As a typical inspiration is 500ml (this varies of course) then in this case the total inspired air is deadspace air, and there will only be minimal mixing of fresh and stale air, not sufficient to properly oxygenate the alveoli and remove CO2.

[my respiratory physiology isnt that strong, btw, I'm best once we get stuff inside the body, so to speak, and my physics is **** poor]

Originally Posted by K

*Sorry, it's the student response.*

Go away and caluculate the deadspace of the horse, sorry 'pony'.

*Standard lecturer response faced with veteriniary students.

Oh, and the reason I am worrying about this is people mostly say volume of tube and some say length and I am trying to work out the determinant.

Originally Posted by yorkie_chris

Forgot to mention ... you silly medic, physicists are no good in the real world, you want an engineer

Dont they all just fiddle with computers these days





and mend TVs and washing machines

[Richie]

Originally Posted by Dr Rich

Dont they all just fiddle with computers these days





and mend TVs and washing machines

Just like bad porn movies... bowchickawowwow...
wait this porn films not ready yet...
Why is that man fixing that washing machine...?